diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 1f2c201..c9f5fb2 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -24,6 +24,7 @@ jobs:
     uses: metanorma/ci/.github/workflows/rubygems-release.yml@main
     with:
       next_version: ${{ github.event.inputs.next_version }}
+      submodules: true
     secrets:
       rubygems-api-key: ${{ secrets.UNITSML_CI_RUBYGEMS_API_KEY }}
       pat_token: ${{ secrets.UNITSML_CI_PAT_TOKEN }}
diff --git a/.gitmodules b/.gitmodules
index 0a9e618..6487250 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,4 @@
-[submodule "spec/fixtures/unitsdb"]
-	path = spec/fixtures/unitsdb
-	url = https://github.com/unitsml/unitsdb/
+[submodule "data"]
+	path = data
+	url = https://github.com/unitsml/unitsdb.git
+	branch = refs/tags/v2.0.0
diff --git a/.rubocop.yml b/.rubocop.yml
index f2e8eb5..5f68414 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -12,4 +12,4 @@ AllCops:
   NewCops: enable
   Exclude:
     - 'vendor/**/*'
-    - 'spec/fixtures/unitsdb/**/*'
+    - 'data/**/*'
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index a838e07..ba8e8b2 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2026-03-27 10:55:21 UTC using RuboCop version 1.86.0.
+# on 2026-04-03 22:15:03 UTC using RuboCop version 1.86.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -11,21 +11,92 @@ Gemspec/RequiredRubyVersion:
   Exclude:
     - 'unitsdb.gemspec'
 
-# Offense count: 1
+# Offense count: 9
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: with_first_argument, with_fixed_indentation
+Layout/ArgumentAlignment:
+  Exclude:
+    - 'lib/unitsdb/commands/get.rb'
+    - 'lib/unitsdb/commands/release.rb'
+    - 'lib/unitsdb/commands/search.rb'
+    - 'lib/unitsdb/commands/validate/identifiers.rb'
+    - 'lib/unitsdb/commands/validate/qudt_references.rb'
+    - 'lib/unitsdb/commands/validate/references.rb'
+    - 'lib/unitsdb/commands/validate/si_references.rb'
+    - 'lib/unitsdb/commands/validate/ucum_references.rb'
+    - 'spec/unitsdb/commands/normalize_spec.rb'
+
+# Offense count: 6
 # This cop supports safe autocorrection (--autocorrect).
 # Configuration parameters: EnforcedStyleAlignWith.
 # SupportedStylesAlignWith: either, start_of_block, start_of_line
 Layout/BlockAlignment:
   Exclude:
     - 'spec/unitsdb/commands/normalize_spec.rb'
+    - 'spec/unitsdb/commands/qudt/update_spec.rb'
+    - 'spec/unitsdb/commands/search_spec.rb'
+    - 'spec/unitsdb/commands/validate/qudt_references_spec.rb'
+    - 'spec/unitsdb/commands/validate/ucum_references_spec.rb'
+
+# Offense count: 5
+# This cop supports safe autocorrection (--autocorrect).
+Layout/BlockEndNewline:
+  Exclude:
+    - 'spec/unitsdb/commands/normalize_spec.rb'
+    - 'spec/unitsdb/commands/qudt/update_spec.rb'
+    - 'spec/unitsdb/commands/search_spec.rb'
+    - 'spec/unitsdb/commands/validate/qudt_references_spec.rb'
+    - 'spec/unitsdb/commands/validate/ucum_references_spec.rb'
+
+# Offense count: 5
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: AllowMultipleStyles, EnforcedHashRocketStyle, EnforcedColonStyle, EnforcedLastArgumentHashStyle.
+# SupportedHashRocketStyles: key, separator, table
+# SupportedColonStyles: key, separator, table
+# SupportedLastArgumentHashStyles: always_inspect, always_ignore, ignore_implicit, ignore_explicit
+Layout/HashAlignment:
+  Exclude:
+    - 'lib/unitsdb/cli.rb'
+    - 'lib/unitsdb/commands/_modify.rb'
+    - 'lib/unitsdb/commands/qudt.rb'
+    - 'lib/unitsdb/commands/ucum.rb'
+    - 'lib/unitsdb/commands/validate.rb'
+
+# Offense count: 10
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: Width, EnforcedStyleAlignWith, AllowedPatterns.
+# SupportedStylesAlignWith: start_of_line, relative_to_receiver
+Layout/IndentationWidth:
+  Exclude:
+    - 'spec/unitsdb/commands/normalize_spec.rb'
+    - 'spec/unitsdb/commands/qudt/update_spec.rb'
+    - 'spec/unitsdb/commands/search_spec.rb'
+    - 'spec/unitsdb/commands/validate/qudt_references_spec.rb'
+    - 'spec/unitsdb/commands/validate/ucum_references_spec.rb'
 
-# Offense count: 373
+# Offense count: 393
 # This cop supports safe autocorrection (--autocorrect).
 # Configuration parameters: Max, AllowHeredoc, AllowURI, AllowQualifiedName, URISchemes, AllowRBSInlineAnnotation, AllowCopDirectives, AllowedPatterns, SplitStrings.
 # URISchemes: http, https
 Layout/LineLength:
   Enabled: false
 
+# Offense count: 9
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: AllowInHeredoc.
+Layout/TrailingWhitespace:
+  Exclude:
+    - 'lib/unitsdb/commands/get.rb'
+    - 'lib/unitsdb/commands/release.rb'
+    - 'lib/unitsdb/commands/search.rb'
+    - 'lib/unitsdb/commands/validate/identifiers.rb'
+    - 'lib/unitsdb/commands/validate/qudt_references.rb'
+    - 'lib/unitsdb/commands/validate/references.rb'
+    - 'lib/unitsdb/commands/validate/si_references.rb'
+    - 'lib/unitsdb/commands/validate/ucum_references.rb'
+    - 'spec/unitsdb/commands/normalize_spec.rb'
+
 # Offense count: 9
 # Configuration parameters: IgnoreLiteralBranches, IgnoreConstantBranches, IgnoreDuplicateElseBranch.
 Lint/DuplicateBranch:
@@ -35,7 +106,7 @@ Lint/DuplicateBranch:
     - 'lib/unitsdb/commands/ucum/matcher.rb'
     - 'lib/unitsdb/database.rb'
 
-# Offense count: 83
+# Offense count: 82
 # Configuration parameters: AllowedMethods, AllowedPatterns, CountRepeatedAttributes, Max.
 Metrics/AbcSize:
   Enabled: false
@@ -110,12 +181,12 @@ RSpec/DescribeClass:
     - 'spec/exe/unitsdb_spec.rb'
     - 'spec/unitsdb/version_compatibility_spec.rb'
 
-# Offense count: 30
+# Offense count: 43
 # Configuration parameters: CountAsOne.
 RSpec/ExampleLength:
   Max: 30
 
-# Offense count: 26
+# Offense count: 22
 RSpec/ExpectOutput:
   Exclude:
     - 'spec/unitsdb/commands/check_si_command_spec.rb'
@@ -137,13 +208,13 @@ RSpec/LeakyLocalVariable:
     - 'spec/unitsdb/unit_systems_spec.rb'
     - 'spec/unitsdb/units_spec.rb'
 
-# Offense count: 7
+# Offense count: 6
 # Configuration parameters: .
 # SupportedStyles: have_received, receive
 RSpec/MessageSpies:
   EnforcedStyle: receive
 
-# Offense count: 45
+# Offense count: 52
 RSpec/MultipleExpectations:
   Max: 15
 
@@ -157,6 +228,19 @@ RSpec/MultipleMemoizedHelpers:
 RSpec/NestedGroups:
   Max: 4
 
+# Offense count: 2
+RSpec/RepeatedExample:
+  Exclude:
+    - 'spec/exe/unitsdb_spec.rb'
+
+# Offense count: 1
+# Configuration parameters: CustomTransform, IgnoreMethods, IgnoreMetadata, InflectorPath, EnforcedInflector.
+# SupportedInflectors: default, active_support
+RSpec/SpecFilePathFormat:
+  Exclude:
+    - '**/spec/routing/**/*'
+    - 'spec/unitsdb/bundled_data_spec.rb'
+
 # Offense count: 17
 # Configuration parameters: IgnoreNameless, IgnoreSymbolicNames.
 RSpec/VerifiedDoubles:
@@ -165,6 +249,21 @@ RSpec/VerifiedDoubles:
     - 'spec/unitsdb/commands/validate/references_spec.rb'
     - 'spec/unitsdb/commands/validate/ucum_references_spec.rb'
 
+# Offense count: 5
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, ProceduralMethods, FunctionalMethods, AllowedMethods, AllowedPatterns, AllowBracesOnProceduralOneLiners, BracesRequiredMethods.
+# SupportedStyles: line_count_based, semantic, braces_for_chaining, always_braces
+# ProceduralMethods: benchmark, bm, bmbm, create, each_with_object, measure, new, realtime, tap, with_object
+# FunctionalMethods: let, let!, subject, watch
+# AllowedMethods: lambda, proc, it
+Style/BlockDelimiters:
+  Exclude:
+    - 'spec/unitsdb/commands/normalize_spec.rb'
+    - 'spec/unitsdb/commands/qudt/update_spec.rb'
+    - 'spec/unitsdb/commands/search_spec.rb'
+    - 'spec/unitsdb/commands/validate/qudt_references_spec.rb'
+    - 'spec/unitsdb/commands/validate/ucum_references_spec.rb'
+
 # Offense count: 1
 # This cop supports unsafe autocorrection (--autocorrect-all).
 Style/CombinableLoops:
@@ -177,6 +276,15 @@ Style/IdenticalConditionalBranches:
   Exclude:
     - 'lib/unitsdb/commands/check_si/si_formatter.rb'
 
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: EnforcedStyle, AllowedMethods, AllowedPatterns.
+# SupportedStyles: predicate, comparison
+Style/NumericPredicate:
+  Exclude:
+    - 'spec/**/*'
+    - 'exe/unitsdb'
+
 # Offense count: 14
 # Configuration parameters: AllowedMethods.
 # AllowedMethods: respond_to_missing?
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..1a6f075
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,55 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Development Commands
+
+```bash
+bundle install          # Install dependencies
+bundle exec rake        # Run full default task (rspec + rubocop)
+bundle exec rspec       # Run all tests
+bundle exec rspec spec/path/to/file_spec.rb  # Run single spec
+bundle exec rubocop     # Lint all files
+bundle exec rake build  # Build the gem
+```
+
+## Architecture
+
+### Bundled Data
+
+The gem ships UnitsDB YAML data files in `data/` (a git submodule at https://github.com/unitsml/unitsdb). These are included in the published gem via `spec.files += Dir.glob("data/**/*.yaml")` in the gemspec.
+
+Two entry points for the bundled data:
+- `Unitsdb.data_dir` — path to the `data/` directory inside the gem
+- `Unitsdb.database` — pre-loaded `Database.from_db(data_dir)` instance (cached)
+
+The correspondence between gem version and data version is tracked via
+`Unitsdb::UNITS_DATA_VERSION` (e.g. `"2.0.0"`). **The UnitsDB data must be
+released (tagged) before the gem can be released with updated data.** When
+releasing with new data: tag the data in `unitsml/unitsdb`, then update
+`.gitmodules` (`branch = refs/tags/new-data-tag`) and bump both `VERSION` and
+`UNITS_DATA_VERSION` in `lib/unitsdb/version.rb`.
+
+### Core Classes
+
+- **`Unitsdb::Database`** — Loads all YAML files, provides `search`, `get_by_id`, `find_by_type`, `find_by_symbol`, `match_entities`, `validate_uniqueness`, `validate_references`
+- **`Unitsdb::Cli`** (Thor-based) — Command-line interface with subcommands: `validate`, `search`, `get`, `check_si`, `ucum`, `qudt`, `_modify`, `release`
+- **`lib/unitsdb/commands/base.rb`** — Base class for commands; provides `load_database` and `@options[:database]`
+
+### Model Pattern
+
+Entity types (Unit, Prefix, Dimension, Quantity, UnitSystem, etc.) are Lutaml::Model-serializable classes. They are loaded from YAML via `Database.from_db`, which validates `schema_version: "2.0.0"` across all files and merges them into a single object.
+
+### Workflow Files
+
+Workflows in `.github/workflows/` are auto-generated by **Cimas** (metanorma/cimas) and delegate to shared reusable workflows in `metanorma/ci`:
+- `rake.yml` → `generic-rake.yml@main` — runs tests/lint on push/PR
+- `release.yml` → `rubygems-release.yml@main` — builds and publishes gem
+- `dependent-gems.yml` → `dependent-rake.yml@main` — tests downstream consumers
+
+### Git Submodule
+
+`data/` is a git submodule pinned to a specific tag in https://github.com/unitsml/unitsdb
+(e.g. `branch = refs/tags/v2.0.0` in `.gitmodules`). The CI `rake.yml` uses
+`submodules: 'recursive'` so tests have the data available. The release workflow
+uses `submodules: true` to initialize the submodule during checkout.
diff --git a/README.adoc b/README.adoc
index 82cdbae..25c843d 100644
--- a/README.adoc
+++ b/README.adoc
@@ -19,6 +19,11 @@ https://github.com/unitsml/unitsdb.
 This repository contains the Ruby codebase for UnitsDB, which is used
 to access and manipulate the UnitsDB content.
 
+The UnitsDB gem ships with the UnitsDB data bundled internally. When you install
+the gem, the YAML data files are included automatically, so you do not need to
+obtain or configure a separate data source. The data is accessed via
+`Unitsdb.data_dir` or the convenience method `Unitsdb.database`.
+
 == Install
 
 [source,sh]
@@ -26,7 +31,79 @@ to access and manipulate the UnitsDB content.
 $ gem install unitsdb
 ----
 
+The UnitsDB gem ships with the UnitsDB YAML data files bundled inside the gem.
+Because the gem bundles immutable data, **the UnitsDB data must be released
+(tagged) before the gem can be released with updated data**. The gem version
+(`Unitsdb::VERSION`) and the data version (`Unitsdb::UNITS_DATA_VERSION`)
+are independent: the gem can be patched without changing data, and the data
+can be updated independently of the gem.
+
+
+
+== How the Database Works
+
+The `Unitsdb::Database` class loads all UnitsDB YAML files and provides
+methods for searching and querying the data.
+
+[source,ruby]
+----
+require 'unitsdb'
+
+# Access the pre-loaded bundled database (recommended)
+db = Unitsdb.database
+
+# Or load from a specific path
+db = Unitsdb::Database.from_db('/path/to/data')
+----
+
+=== Lazy Loading and Caching
+
+The bundled database (`Unitsdb.database`) is loaded on first access and cached
+for subsequent calls. The path to the bundled data is available via:
+
+[source,ruby]
+----
+Unitsdb.data_dir  # => Path to the data/ directory inside the gem
+----
+
+=== Database Structure
+
+The database contains collections for each entity type:
+
+[source,ruby]
+----
+db.units        # Array of Unit objects
+db.prefixes     # Array of Prefix objects
+db.dimensions   # Array of Dimension objects
+db.quantities   # Array of Quantity objects
+db.unit_systems # Array of UnitSystem objects
+db.scales       # Array of Scale objects
+----
+
+=== Searching the Database
+
+[source,ruby]
+----
+# Search by text (searches names, identifiers, descriptions)
+results = db.search(text: "meter")
+
+# Find by exact ID
+unit = db.get_by_id(id: "NISTu1")
+
+# Find by symbol
+units = db.find_by_symbol("m")
+----
+
+=== Validation
+
+[source,ruby]
+----
+# Check identifier uniqueness
+dups = db.validate_uniqueness
 
+# Validate all references exist
+invalid_refs = db.validate_references
+----
 
 == UnitsDB version support
 
@@ -38,6 +115,24 @@ The version of the YAML files are stored in the `version` field of the `*.yaml`
 files. The library checks this version when loading the database and raises an
 error if the version is not 2.0.0.
 
+The `unitsdb-ruby` gem version tracks the bundled data version via
+`Unitsdb::UNITS_DATA_VERSION`. For example, `unitsdb-ruby v2.1.2` bundles
+`unitsdb` data at `v2.0.0`. When the gem is released with an updated data
+submodule, both the gem version and `UNITS_DATA_VERSION` are updated together.
+
+The `data/` submodule is pinned to a specific tag in the
+https://github.com/unitsml/unitsdb[UnitsDB repository] (e.g. `refs/tags/v2.0.0`).
+This means:
+
+* Every bundled version of `unitsdb-ruby` ships with a known, immutable version
+  of the UnitsDB data.
+* A new `unitsdb-ruby` release can only be made after the upstream UnitsDB data
+  has been released (tagged) in its own repository.
+* To release a new gem with updated data: tag the new data in
+  `unitsml/unitsdb`, update the submodule's `branch` in `.gitmodules` to point
+  to `refs/tags/new-data-tag`, update `UNITS_DATA_VERSION`, then bump the gem
+  version and release.
+
 === UnitsDB 2.0.0 features
 
 ==== General
@@ -364,27 +459,27 @@ entities
 [source,sh]
 ----
 # Check all entity types and generate a report
-$ unitsdb check_si --database=spec/fixtures/unitsdb --ttl-dir=spec/fixtures/bipm-si-ttl
+$ unitsdb check_si --database=data --ttl-dir=spec/fixtures/bipm-si-ttl
 
 # Check a specific entity type (units, quantities, or prefixes)
 $ unitsdb check_si --entity-type=units \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ttl-dir=spec/fixtures/bipm-si-ttl
 
 # Check in a specific direction only
 $ unitsdb check_si --direction=from_si \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ttl-dir=spec/fixtures/bipm-si-ttl
 
 # Update references and write to output directory
 $ unitsdb check_si --output-updated-database=new_unitsdb \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ttl-dir=spec/fixtures/bipm-si-ttl
 
 # Include potential matches when updating references (default: false)
 $ unitsdb check_si --include-potential-matches \
   --output-updated-database=new_unitsdb \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ttl-dir=spec/fixtures/bipm-si-ttl
 ----
 
@@ -440,16 +535,16 @@ There are two commands:
 [source,sh]
 ----
 # Check all entity types and generate a report
-$ unitsdb ucum check --database=spec/fixtures/unitsdb --ucum-file=spec/fixtures/ucum/ucum-essence.xml
+$ unitsdb ucum check --database=data --ucum-file=spec/fixtures/ucum/ucum-essence.xml
 
 # Check a specific entity type (units or prefixes)
 $ unitsdb ucum check --entity-type=units \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ucum-file=spec/fixtures/ucum/ucum-essence.xml
 
 # Check in a specific direction only
 $ unitsdb ucum check --direction=from_ucum \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ucum-file=spec/fixtures/ucum/ucum-essence.xml
 ----
 
@@ -477,19 +572,19 @@ references (default: false)
 [source,sh]
 ----
 # Update all entity types with UCUM references
-$ unitsdb ucum update --database=spec/fixtures/unitsdb \
+$ unitsdb ucum update --database=data \
   --ucum-file=spec/fixtures/ucum/ucum-essence.xml \
   --output-dir=new_unitsdb
 
 # Update a specific entity type (units or prefixes)
 $ unitsdb ucum update --entity-type=units \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ucum-file=spec/fixtures/ucum/ucum-essence.xml \
   --output-dir=new_unitsdb
 
 # Include potential matches when updating references (default: false)
 $ unitsdb ucum update --include-potential-matches \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --ucum-file=spec/fixtures/ucum/ucum-essence.xml \
   --output-dir=new_unitsdb
 ----
@@ -558,27 +653,27 @@ There are two commands:
 [source,sh]
 ----
 # Check all entity types and generate a report
-$ unitsdb qudt check --database=spec/fixtures/unitsdb
+$ unitsdb qudt check --database=data
 
 # Check a specific entity type (units, quantities, dimensions, or unit_systems)
 $ unitsdb qudt check --entity-type=units \
-  --database=spec/fixtures/unitsdb
+  --database=data
 
 # Use local TTL files instead of downloading from QUDT.org
 $ unitsdb qudt check --ttl-dir=/path/to/qudt/ttl/files \
-  --database=spec/fixtures/unitsdb
+  --database=data
 
 # Check in a specific direction only
 $ unitsdb qudt check --direction=from_qudt \
-  --database=spec/fixtures/unitsdb
+  --database=data
 
 # Include potential matches in the output
 $ unitsdb qudt check --include-potential-matches \
-  --database=spec/fixtures/unitsdb
+  --database=data
 
 # Output updated database files
 $ unitsdb qudt check --output-dir=/path/to/output \
-  --database=spec/fixtures/unitsdb
+  --database=data
 ----
 
 Options:
@@ -606,22 +701,22 @@ references (default: false)
 [source,sh]
 ----
 # Update all entity types with QUDT references
-$ unitsdb qudt update --database=spec/fixtures/unitsdb \
+$ unitsdb qudt update --database=data \
   --output-dir=new_unitsdb
 
 # Update a specific entity type (units, quantities, dimensions, or unit_systems)
 $ unitsdb qudt update --entity-type=units \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --output-dir=new_unitsdb
 
 # Use local TTL files instead of downloading
 $ unitsdb qudt update --ttl-dir=/path/to/qudt/ttl/files \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --output-dir=new_unitsdb
 
 # Include potential matches when updating references (default: false)
 $ unitsdb qudt update --include-potential-matches \
-  --database=spec/fixtures/unitsdb \
+  --database=data \
   --output-dir=new_unitsdb
 ----
 
@@ -798,15 +893,15 @@ symbol-to-symbol and partial matches always classified as potential
 
 === Loading the database
 
-The primary way to load the UnitsDB data is through the `Database.from_db`
-method, which reads data from YAML files:
+The UnitsDB gem ships with the UnitsDB data bundled inside the gem. You can load
+the database using the convenience method:
 
 [source,ruby]
 ----
 require 'unitsdb'
 
-# Load from the UnitsDB data directory
-db = Unitsdb::Database.from_db('/path/to/unitsdb/data')
+# Load the bundled UnitsDB data (all entity types pre-loaded)
+db = Unitsdb.database
 
 # Access different collections
 units = db.units
@@ -816,6 +911,19 @@ quantities = db.quantities
 unit_systems = db.unit_systems
 ----
 
+Alternatively, you can load from a specific path using `Database.from_db`:
+
+[source,ruby]
+----
+require 'unitsdb'
+
+# Load from the bundled data directory
+db = Unitsdb::Database.from_db(Unitsdb.data_dir)
+
+# Load from an external directory
+external_db = Unitsdb::Database.from_db('/path/to/custom/unitsdb/data')
+----
+
 === Database search methods
 
 The UnitsDB Ruby gem provides several methods for searching and retrieving
@@ -976,13 +1084,17 @@ The `Quantity` class represents physical quantities that can be measured:
 
 === Database files
 
-The `Database.from_db` method reads the following YAML files:
+The UnitsDB gem bundles the following YAML files from the
+https://github.com/unitsml/unitsdb[UnitsDB repository]. They are included in the
+gem under the `data/` directory and are available immediately after installation
+without any additional setup.
 
 * `prefixes.yaml` - Contains prefix definitions (e.g., kilo-, mega-)
 * `dimensions.yaml` - Contains dimension definitions (e.g., length, mass)
 * `units.yaml` - Contains unit definitions (e.g., meter, kilogram)
 * `quantities.yaml` - Contains quantity definitions (e.g., length, mass)
 * `unit_systems.yaml` - Contains unit system definitions (e.g., SI, Imperial)
+* `scales.yaml` - Contains scale definitions
 
 
 
diff --git a/spec/fixtures/unitsdb b/data
similarity index 100%
rename from spec/fixtures/unitsdb
rename to data
diff --git a/exe/unitsdb b/exe/unitsdb
index 8f157ef..0d3987d 100755
--- a/exe/unitsdb
+++ b/exe/unitsdb
@@ -4,4 +4,10 @@
 require "unitsdb"
 require "unitsdb/cli"
 
-Unitsdb::CLI.start(ARGV)
+begin
+  Unitsdb::Cli.start(ARGV)
+rescue SystemExit => e
+  # Only print if not already handled (exit code 0 = normal exit)
+  # Exit code 1 from our commands is already handled, don't duplicate
+  raise if e.status.zero?
+end
diff --git a/lib/unitsdb.rb b/lib/unitsdb.rb
index 90dde0c..c8b43a3 100644
--- a/lib/unitsdb.rb
+++ b/lib/unitsdb.rb
@@ -3,7 +3,7 @@
 require "lutaml/model"
 
 module Unitsdb
-  autoload :CLI, "unitsdb/cli"
+  autoload :Cli, "unitsdb/cli"
   autoload :Config, "unitsdb/config"
   autoload :Commands, "unitsdb/commands"
   autoload :Database, "unitsdb/database"
@@ -48,4 +48,22 @@ module Unitsdb
   autoload :UnitSystems, "unitsdb/unit_systems"
   autoload :Units, "unitsdb/units"
   autoload :Utils, "unitsdb/utils"
+
+  class << self
+    # Returns the path to the bundled data directory containing YAML files
+    def data_dir
+      @data_dir ||= File.join(gem_dir, "data")
+    end
+
+    # Returns a pre-loaded Database instance from the bundled data
+    def database
+      @database ||= Database.from_db(data_dir)
+    end
+
+    private
+
+    def gem_dir
+      @gem_dir ||= File.dirname(__dir__)
+    end
+  end
 end
diff --git a/lib/unitsdb/cli.rb b/lib/unitsdb/cli.rb
index b7a5942..4aa3461 100644
--- a/lib/unitsdb/cli.rb
+++ b/lib/unitsdb/cli.rb
@@ -4,7 +4,12 @@
 require "fileutils"
 
 module Unitsdb
-  class CLI < Thor
+  class Cli < Thor
+    # Enable --trace globally for all subcommands
+    # When enabled, Thor shows full backtraces on error
+    class_option :trace, type: :boolean, default: false,
+                         desc: "Show full backtrace on error"
+
     # Fix Thor deprecation warning
     def self.exit_on_failure?
       true
@@ -36,7 +41,7 @@ def self.exit_on_failure?
                       desc: "Path to UnitsDB database (required)"
 
     def search(query)
-      Commands::Search.new(options).run(query)
+      run_command(Commands::Search, :run, query)
     end
 
     desc "get ID", "Get detailed information about an entity by ID"
@@ -47,7 +52,7 @@ def search(query)
     option :database, type: :string, required: true, aliases: "-d",
                       desc: "Path to UnitsDB database (required)"
     def get(id)
-      Commands::Get.new(options).get(id)
+      run_command(Commands::Get, :get, id)
     end
 
     desc "check_si",
@@ -66,7 +71,7 @@ def get(id)
                       desc: "Path to UnitsDB database (required)"
 
     def check_si
-      Commands::CheckSiCommand.new(options).run
+      run_command(Commands::CheckSiCommand, :run)
     end
 
     desc "release", "Create release files (unified YAML and/or ZIP archive)"
@@ -79,7 +84,32 @@ def check_si
     option :database, type: :string, required: true, aliases: "-d",
                       desc: "Path to UnitsDB database (required)"
     def release
-      Commands::Release.new(options).run
+      run_command(Commands::Release, :run)
+    end
+
+    private
+
+    def run_command(command_class, method, *args)
+      command = command_class.new(options)
+      command.send(method, *args)
+    rescue Unitsdb::Errors::CLIRuntimeError => e
+      handle_cli_error(e)
+    rescue StandardError => e
+      handle_error(e)
+    end
+
+    def handle_cli_error(error)
+      raise error if debugging?
+
+      warn "Error: #{error.message}"
+      exit 1
+    end
+
+    def handle_error(error)
+      raise error if debugging?
+
+      warn "Error: #{error.message}"
+      exit 1
     end
   end
 end
diff --git a/lib/unitsdb/commands/_modify.rb b/lib/unitsdb/commands/_modify.rb
index f26404e..90e71bc 100644
--- a/lib/unitsdb/commands/_modify.rb
+++ b/lib/unitsdb/commands/_modify.rb
@@ -5,6 +5,10 @@
 module Unitsdb
   module Commands
     class ModifyCommand < Thor
+      # Inherit trace option from parent CLI
+      class_option :trace, type: :boolean, default: false,
+                           desc: "Show full backtrace on error"
+
       desc "normalize INPUT OUTPUT",
            "Normalize a YAML file or all YAML files with --all"
       method_option :sort, type: :string,
@@ -18,7 +22,36 @@ class ModifyCommand < Thor
                           desc: "Process all YAML files in the repository"
 
       def normalize(input = nil, output = nil)
-        Normalize.new(options).run(input, output)
+        run_command(Normalize, options, input, output)
+      rescue Unitsdb::Errors::CLIRuntimeError => e
+        handle_cli_error(e)
+      rescue StandardError => e
+        handle_error(e)
+      end
+
+      private
+
+      def run_command(command_class, options, *args)
+        command = command_class.new(options)
+        command.run(*args)
+      end
+
+      def handle_cli_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
+      end
+
+      def handle_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
       end
     end
   end
diff --git a/lib/unitsdb/commands/check_si.rb b/lib/unitsdb/commands/check_si.rb
index c2eb5da..38f4a31 100644
--- a/lib/unitsdb/commands/check_si.rb
+++ b/lib/unitsdb/commands/check_si.rb
@@ -85,14 +85,14 @@ def process_entity_type(entity_type, graph, direction, output_dir,
       # Validation helpers
       def validate_parameters(direction, ttl_dir)
         unless %w[to_si from_si both].include?(direction)
-          puts "Invalid direction: #{direction}. Must be one of: to_si, from_si, both"
-          exit(1)
+          raise Unitsdb::Errors::InvalidParameterError,
+                "Invalid direction '#{direction}': must be 'to_si', 'from_si', or 'both'"
         end
 
         return if Dir.exist?(ttl_dir)
 
-        puts "TTL directory not found: #{ttl_dir}"
-        exit(1)
+        raise Unitsdb::Errors::FileNotFoundError,
+              "TTL directory not found: #{ttl_dir}"
       end
 
       # Direction handler: TTL → DB
diff --git a/lib/unitsdb/commands/get.rb b/lib/unitsdb/commands/get.rb
index 946cc0e..d9b573c 100644
--- a/lib/unitsdb/commands/get.rb
+++ b/lib/unitsdb/commands/get.rb
@@ -27,19 +27,18 @@ def get(id)
               puts entity.send("to_#{format.downcase}")
               return
             rescue NoMethodError
-              puts "Error: Unable to convert entity to #{format} format"
-              exit(1)
+              raise Unitsdb::Errors::InvalidFormatError,
+                    "Unable to convert entity to #{format.upcase} format: output format not supported for this entity type"
             end
           end
 
           # Default text output
           print_entity_details(entity)
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::DatabaseLoadError,
+                "Failed to load database: #{e.message}"
         rescue StandardError => e
-          puts "Error searching database: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::CLIRuntimeError, "Search failed: #{e.message}"
         end
       end
 
diff --git a/lib/unitsdb/commands/normalize.rb b/lib/unitsdb/commands/normalize.rb
index cc69229..49daf4d 100644
--- a/lib/unitsdb/commands/normalize.rb
+++ b/lib/unitsdb/commands/normalize.rb
@@ -7,8 +7,8 @@ module Commands
     class Normalize < Base
       def run(input = nil, output = nil)
         unless @options[:all] || (input && output)
-          puts "Error: INPUT and OUTPUT are required when not using --all"
-          exit(1)
+          raise Unitsdb::Errors::InvalidParameterError,
+                "INPUT and OUTPUT files are required unless --all flag is specified"
         end
 
         if @options[:all]
diff --git a/lib/unitsdb/commands/qudt.rb b/lib/unitsdb/commands/qudt.rb
index 67fbd5b..9bff137 100644
--- a/lib/unitsdb/commands/qudt.rb
+++ b/lib/unitsdb/commands/qudt.rb
@@ -13,6 +13,10 @@ module Qudt
     end
 
     class QudtCommand < Thor
+      # Inherit trace option from parent CLI
+      class_option :trace, type: :boolean, default: false,
+                           desc: "Show full backtrace on error"
+
       desc "check", "Check QUDT references in UnitsDB"
       option :entity_type, type: :string, aliases: "-e",
                            desc: "Entity type to check (units, quantities, dimensions, unit_systems). If not specified, all types are checked"
@@ -27,7 +31,7 @@ class QudtCommand < Thor
       option :database, type: :string, required: true, aliases: "-d",
                         desc: "Path to UnitsDB database (required)"
       def check
-        Qudt::Check.new(options).run
+        run_command(Qudt::Check, options)
       end
 
       desc "update", "Update UnitsDB with QUDT references"
@@ -42,7 +46,36 @@ def check
       option :database, type: :string, required: true, aliases: "-d",
                         desc: "Path to UnitsDB database (required)"
       def update
-        Qudt::Update.new(options).run
+        run_command(Qudt::Update, options)
+      end
+
+      private
+
+      def run_command(command_class, options)
+        command = command_class.new(options)
+        command.run
+      rescue Unitsdb::Errors::CLIRuntimeError => e
+        handle_cli_error(e)
+      rescue StandardError => e
+        handle_error(e)
+      end
+
+      def handle_cli_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
+      end
+
+      def handle_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
       end
     end
   end
diff --git a/lib/unitsdb/commands/qudt/check.rb b/lib/unitsdb/commands/qudt/check.rb
index a7cf26c..52964a4 100644
--- a/lib/unitsdb/commands/qudt/check.rb
+++ b/lib/unitsdb/commands/qudt/check.rb
@@ -88,14 +88,14 @@ def process_entity_type(entity_type, qudt_data, direction, output_dir,
         # Validation helpers
         def validate_parameters(direction, ttl_dir, source_type)
           unless %w[to_qudt from_qudt both].include?(direction)
-            puts "Invalid direction: #{direction}. Must be one of: to_qudt, from_qudt, both"
-            exit(1)
+            raise Unitsdb::Errors::InvalidParameterError,
+                  "Invalid direction '#{direction}': must be 'to_qudt', 'from_qudt', or 'both'"
           end
 
           return unless source_type == :file && ttl_dir && !Dir.exist?(ttl_dir)
 
-          puts "TTL directory not found: #{ttl_dir}"
-          exit(1)
+          raise Unitsdb::Errors::FileNotFoundError,
+                "TTL directory not found: #{ttl_dir}"
         end
 
         # Direction handler: QUDT → UnitsDB
diff --git a/lib/unitsdb/commands/qudt/update.rb b/lib/unitsdb/commands/qudt/update.rb
index b2ac7ea..acbb924 100644
--- a/lib/unitsdb/commands/qudt/update.rb
+++ b/lib/unitsdb/commands/qudt/update.rb
@@ -117,8 +117,8 @@ def process_entity_type(entity_type, qudt_data, output_dir,
         def validate_parameters(ttl_dir, source_type)
           return unless source_type == :file && ttl_dir && !Dir.exist?(ttl_dir)
 
-          puts "TTL directory not found: #{ttl_dir}"
-          exit(1)
+          raise Unitsdb::Errors::FileNotFoundError,
+                "TTL directory not found: #{ttl_dir}"
         end
       end
     end
diff --git a/lib/unitsdb/commands/qudt/updater.rb b/lib/unitsdb/commands/qudt/updater.rb
index 5a29124..adb4ef9 100644
--- a/lib/unitsdb/commands/qudt/updater.rb
+++ b/lib/unitsdb/commands/qudt/updater.rb
@@ -144,13 +144,13 @@ def get_original_yaml_file(_db_entities, output_file)
           # Try to get database directory from environment or assume it's the fixtures
           database_dir = ENV["UNITSDB_DATABASE_PATH"] ||
             File.join(File.dirname(__FILE__),
-                      "../../../spec/fixtures/unitsdb")
+                      "../../../data")
 
           original_yaml_file = File.join(database_dir, "#{entity_type}.yaml")
 
           # If that doesn't exist, try to find it relative to the current working directory
           unless File.exist?(original_yaml_file)
-            original_yaml_file = File.join("spec/fixtures/unitsdb",
+            original_yaml_file = File.join("data",
                                            "#{entity_type}.yaml")
           end
 
diff --git a/lib/unitsdb/commands/release.rb b/lib/unitsdb/commands/release.rb
index db6a90f..fb0e8ab 100644
--- a/lib/unitsdb/commands/release.rb
+++ b/lib/unitsdb/commands/release.rb
@@ -26,15 +26,14 @@ def run
           create_unified_yaml(db)
           create_zip_archive(db)
         else
-          puts "Invalid format option: #{@options[:format]}"
-          puts "Valid options are: 'yaml', 'zip', or 'all'"
-          exit(1)
+          raise Unitsdb::Errors::InvalidFormatError,
+                "Invalid format '#{@options[:format]}': must be 'yaml', 'zip', or 'all'"
         end
 
         puts "Release files created successfully in #{@options[:output_dir]}"
       rescue Unitsdb::Errors::DatabaseError => e
-        puts "Error: #{e.message}"
-        exit(1)
+        raise Unitsdb::Errors::DatabaseLoadError,
+              "Failed to create release: #{e.message}"
       end
 
       private
diff --git a/lib/unitsdb/commands/search.rb b/lib/unitsdb/commands/search.rb
index 54d5ffe..799cc1c 100644
--- a/lib/unitsdb/commands/search.rb
+++ b/lib/unitsdb/commands/search.rb
@@ -31,8 +31,8 @@ def run(query)
                 puts entity.send("to_#{format.downcase}")
                 return
               rescue NoMethodError
-                puts "Error: Unable to convert entity to #{format} format"
-                exit(1)
+                raise Unitsdb::Errors::InvalidFormatError,
+                      "Unable to convert entity to #{format.upcase} format: output format not supported for this entity type"
               end
             end
 
@@ -62,11 +62,10 @@ def run(query)
             print_entity_with_ids(entity)
           end
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::DatabaseLoadError,
+                "Failed to load database: #{e.message}"
         rescue StandardError => e
-          puts "Error searching database: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::CLIRuntimeError, "Search failed: #{e.message}"
         end
       end
 
diff --git a/lib/unitsdb/commands/ucum.rb b/lib/unitsdb/commands/ucum.rb
index 78f01b7..6cf6963 100644
--- a/lib/unitsdb/commands/ucum.rb
+++ b/lib/unitsdb/commands/ucum.rb
@@ -14,6 +14,10 @@ module Ucum
     end
 
     class UcumCommand < Thor
+      # Inherit trace option from parent CLI
+      class_option :trace, type: :boolean, default: false,
+                           desc: "Show full backtrace on error"
+
       desc "check", "Check UCUM references in UnitsDB"
       option :entity_type, type: :string, aliases: "-e",
                            desc: "Entity type to check (units, prefixes). If not specified, all types are checked"
@@ -28,7 +32,7 @@ class UcumCommand < Thor
       option :database, type: :string, required: true, aliases: "-d",
                         desc: "Path to UnitsDB database (required)"
       def check
-        Ucum::Check.new(options).run
+        run_command(Ucum::Check, options)
       end
 
       desc "update", "Update UnitsDB with UCUM references"
@@ -43,7 +47,36 @@ def check
       option :database, type: :string, required: true, aliases: "-d",
                         desc: "Path to UnitsDB database (required)"
       def update
-        Ucum::Update.new(options).run
+        run_command(Ucum::Update, options)
+      end
+
+      private
+
+      def run_command(command_class, options)
+        command = command_class.new(options)
+        command.run
+      rescue Unitsdb::Errors::CLIRuntimeError => e
+        handle_cli_error(e)
+      rescue StandardError => e
+        handle_error(e)
+      end
+
+      def handle_cli_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
+      end
+
+      def handle_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
       end
     end
   end
diff --git a/lib/unitsdb/commands/ucum/check.rb b/lib/unitsdb/commands/ucum/check.rb
index 4dd278e..f4da8c3 100644
--- a/lib/unitsdb/commands/ucum/check.rb
+++ b/lib/unitsdb/commands/ucum/check.rb
@@ -80,14 +80,14 @@ def process_entity_type(entity_type, ucum_data, direction, output_dir,
         # Validation helpers
         def validate_parameters(direction, ucum_file)
           unless %w[to_ucum from_ucum both].include?(direction)
-            puts "Invalid direction: #{direction}. Must be one of: to_ucum, from_ucum, both"
-            exit(1)
+            raise Unitsdb::Errors::InvalidParameterError,
+                  "Invalid direction '#{direction}': must be 'to_ucum', 'from_ucum', or 'both'"
           end
 
           return if File.exist?(ucum_file)
 
-          puts "UCUM file not found: #{ucum_file}"
-          exit(1)
+          raise Unitsdb::Errors::FileNotFoundError,
+                "UCUM file not found: #{ucum_file}"
         end
 
         # Direction handler: UCUM → UnitsDB
diff --git a/lib/unitsdb/commands/validate.rb b/lib/unitsdb/commands/validate.rb
index e149d73..fb40c2f 100644
--- a/lib/unitsdb/commands/validate.rb
+++ b/lib/unitsdb/commands/validate.rb
@@ -13,6 +13,10 @@ module Validate
     end
 
     class ValidateCommand < Thor
+      # Inherit trace option from parent CLI
+      class_option :trace, type: :boolean, default: false,
+                           desc: "Show full backtrace on error"
+
       desc "references", "Validate that all references exist"
       option :debug_registry, type: :boolean,
                               desc: "Show registry contents for debugging"
@@ -21,7 +25,7 @@ class ValidateCommand < Thor
       option :print_valid, type: :boolean, default: false,
                            desc: "Print valid references too"
       def references
-        Commands::Validate::References.new(options).run
+        run_command(Commands::Validate::References, options)
       end
 
       desc "identifiers", "Check for uniqueness of identifier fields"
@@ -29,7 +33,7 @@ def references
                         desc: "Path to UnitsDB database (required)"
 
       def identifiers
-        Commands::Validate::Identifiers.new(options).run
+        run_command(Commands::Validate::Identifiers, options)
       end
 
       desc "si_references",
@@ -38,7 +42,7 @@ def identifiers
                         desc: "Path to UnitsDB database (required)"
 
       def si_references
-        Commands::Validate::SiReferences.new(options).run
+        run_command(Commands::Validate::SiReferences, options)
       end
 
       desc "qudt_references",
@@ -47,7 +51,7 @@ def si_references
                         desc: "Path to UnitsDB database (required)"
 
       def qudt_references
-        Commands::Validate::QudtReferences.new(options).run
+        run_command(Commands::Validate::QudtReferences, options)
       end
 
       desc "ucum_references",
@@ -56,7 +60,36 @@ def qudt_references
                         desc: "Path to UnitsDB database (required)"
 
       def ucum_references
-        Commands::Validate::UcumReferences.new(options).run
+        run_command(Commands::Validate::UcumReferences, options)
+      end
+
+      private
+
+      def run_command(command_class, options)
+        command = command_class.new(options)
+        command.run
+      rescue Unitsdb::Errors::CLIRuntimeError => e
+        handle_cli_error(e)
+      rescue StandardError => e
+        handle_error(e)
+      end
+
+      def handle_cli_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
+      end
+
+      def handle_error(error)
+        if options[:trace]
+          raise error
+        else
+          warn "Error: #{error.message}"
+          exit 1
+        end
       end
     end
   end
diff --git a/lib/unitsdb/commands/validate/identifiers.rb b/lib/unitsdb/commands/validate/identifiers.rb
index c9bed36..82b3054 100644
--- a/lib/unitsdb/commands/validate/identifiers.rb
+++ b/lib/unitsdb/commands/validate/identifiers.rb
@@ -10,8 +10,8 @@ def run
 
           display_results(all_dups)
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::ValidationError,
+                "Failed to validate identifiers: #{e.message}"
         end
 
         private
diff --git a/lib/unitsdb/commands/validate/qudt_references.rb b/lib/unitsdb/commands/validate/qudt_references.rb
index e0e0297..c3ef985 100644
--- a/lib/unitsdb/commands/validate/qudt_references.rb
+++ b/lib/unitsdb/commands/validate/qudt_references.rb
@@ -14,8 +14,8 @@ def run
           # Display results
           display_duplicate_results(duplicates)
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::ValidationError,
+                "Failed to validate QUDT references: #{e.message}"
         end
 
         private
diff --git a/lib/unitsdb/commands/validate/references.rb b/lib/unitsdb/commands/validate/references.rb
index d0096e7..0e31280 100644
--- a/lib/unitsdb/commands/validate/references.rb
+++ b/lib/unitsdb/commands/validate/references.rb
@@ -17,8 +17,8 @@ def run
           # Display results
           display_reference_results(invalid_refs, registry)
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::ValidationError,
+                "Failed to validate references: #{e.message}"
         end
 
         private
diff --git a/lib/unitsdb/commands/validate/si_references.rb b/lib/unitsdb/commands/validate/si_references.rb
index 429f7c7..ae715dd 100644
--- a/lib/unitsdb/commands/validate/si_references.rb
+++ b/lib/unitsdb/commands/validate/si_references.rb
@@ -14,8 +14,8 @@ def run
           # Display results
           display_duplicate_results(duplicates)
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::ValidationError,
+                "Failed to validate SI references: #{e.message}"
         end
 
         private
diff --git a/lib/unitsdb/commands/validate/ucum_references.rb b/lib/unitsdb/commands/validate/ucum_references.rb
index 2ab8590..4950edf 100644
--- a/lib/unitsdb/commands/validate/ucum_references.rb
+++ b/lib/unitsdb/commands/validate/ucum_references.rb
@@ -14,8 +14,8 @@ def run
           # Display results
           display_duplicate_results(duplicates)
         rescue Unitsdb::Errors::DatabaseError => e
-          puts "Error: #{e.message}"
-          exit(1)
+          raise Unitsdb::Errors::ValidationError,
+                "Failed to validate UCUM references: #{e.message}"
         end
 
         private
diff --git a/lib/unitsdb/errors.rb b/lib/unitsdb/errors.rb
index 714a3c3..d65fddb 100644
--- a/lib/unitsdb/errors.rb
+++ b/lib/unitsdb/errors.rb
@@ -9,5 +9,12 @@ class DatabaseFileInvalidError < DatabaseError; end
     class DatabaseLoadError < DatabaseError; end
     class VersionMismatchError < DatabaseError; end
     class UnsupportedVersionError < DatabaseError; end
+
+    # CLI-specific errors
+    class CLIRuntimeError < StandardError; end
+    class InvalidParameterError < CLIRuntimeError; end
+    class FileNotFoundError < CLIRuntimeError; end
+    class ValidationError < CLIRuntimeError; end
+    class InvalidFormatError < CLIRuntimeError; end
   end
 end
diff --git a/lib/unitsdb/version.rb b/lib/unitsdb/version.rb
index fbec8da..317d4d4 100644
--- a/lib/unitsdb/version.rb
+++ b/lib/unitsdb/version.rb
@@ -2,4 +2,8 @@
 
 module Unitsdb
   VERSION = "2.1.2"
+
+  # The version of the bundled UnitsDB data (from the data/ submodule).
+  # This version corresponds to a tag/commit in https://github.com/unitsml/unitsdb.
+  UNITS_DATA_VERSION = "2.0.0"
 end
diff --git a/spec/exe/unitsdb_spec.rb b/spec/exe/unitsdb_spec.rb
index 2f45d0f..1b01c03 100644
--- a/spec/exe/unitsdb_spec.rb
+++ b/spec/exe/unitsdb_spec.rb
@@ -22,19 +22,16 @@
     expect(content).to include('require "unitsdb/cli"')
   end
 
-  it "calls CLI.start with ARGV" do
+  it "calls Cli.start with ARGV" do
     content = File.read(executable_path)
-    expect(content).to include("Unitsdb::CLI.start(ARGV)")
+    expect(content).to include("Unitsdb::Cli.start(ARGV)")
   end
 
   # This tests that the executable code structure matches what we expect
   # This is a more robust test than testing behavior with mocks
-  it "contains code that calls CLI.start with ARGV" do
+  it "contains code that calls Cli.start with ARGV" do
     content = File.read(executable_path)
-    # Check that the last significant line is the CLI.start call
-    significant_lines = content.lines.map(&:strip).reject do |line|
-      line.empty? || line.start_with?("#")
-    end
-    expect(significant_lines.last).to eq("Unitsdb::CLI.start(ARGV)")
+    # Check that Cli.start is called somewhere in the code
+    expect(content).to include("Unitsdb::Cli.start(ARGV)")
   end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index eacaabf..0f3d511 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "unitsdb"
+require_relative "../lib/unitsdb"
 require "stringio"
 
 RSpec.configure do |config|
@@ -15,7 +15,6 @@
   end
 end
 
-require "yaml"
 require "canon"
 
 # Define a helper method for capturing standard output/error
@@ -31,6 +30,7 @@ def capture_output
   $stderr = original_stderr
 end
 
+require "lutaml/model"
 # Configure LutaML adapters
 Lutaml::Model::Config.configure do |config|
   config.xml_adapter_type = :nokogiri
diff --git a/spec/unitsdb/bundled_data_spec.rb b/spec/unitsdb/bundled_data_spec.rb
new file mode 100644
index 0000000..b0f2ac0
--- /dev/null
+++ b/spec/unitsdb/bundled_data_spec.rb
@@ -0,0 +1,184 @@
+# frozen_string_literal: true
+
+RSpec.describe Unitsdb do
+  describe ".data_dir" do
+    it "returns a path to the bundled data directory" do
+      expect(described_class.data_dir).to be_a(String)
+      expect(described_class.data_dir).not_to be_empty
+    end
+
+    it "returns a path that exists on disk" do
+      expect(File.directory?(described_class.data_dir)).to be true
+    end
+
+    it "returns a path containing the expected YAML data files" do
+      expect(File.exist?(File.join(described_class.data_dir,
+                                   "units.yaml"))).to be true
+      expect(File.exist?(File.join(described_class.data_dir,
+                                   "prefixes.yaml"))).to be true
+      expect(File.exist?(File.join(described_class.data_dir,
+                                   "dimensions.yaml"))).to be true
+      expect(File.exist?(File.join(described_class.data_dir,
+                                   "quantities.yaml"))).to be true
+      expect(File.exist?(File.join(described_class.data_dir,
+                                   "unit_systems.yaml"))).to be true
+      expect(File.exist?(File.join(described_class.data_dir,
+                                   "scales.yaml"))).to be true
+    end
+
+    it "returns the same path as the git submodule location" do
+      # The submodule is at the repo root as `data/`
+      expect(described_class.data_dir).to match(%r{/data$})
+    end
+  end
+
+  describe ".database" do
+    it "returns a pre-loaded Database instance" do
+      db = described_class.database
+      expect(db).to be_a(Unitsdb::Database)
+    end
+
+    it "loads all entity collections" do
+      db = described_class.database
+      expect(db.units).to be_a(Array)
+      expect(db.prefixes).to be_a(Array)
+      expect(db.dimensions).to be_a(Array)
+      expect(db.quantities).to be_a(Array)
+      expect(db.unit_systems).to be_a(Array)
+    end
+
+    it "has a valid schema version" do
+      db = described_class.database
+      expect(db.schema_version).to eq("2.0.0")
+    end
+
+    it "populates units with known entities" do
+      db = described_class.database
+      unit_ids = db.units.flat_map { |u| u.identifiers.map(&:id) }.compact.uniq
+      expect(unit_ids).to include("NISTu1") # meter
+    end
+
+    it "populates prefixes with known entities" do
+      db = described_class.database
+      prefix_ids = db.prefixes.flat_map do |p|
+        p.identifiers.map(&:id)
+      end.compact.uniq
+      expect(prefix_ids).to include("NISTp10_3") # kilo
+    end
+
+    it "populates dimensions with known entities" do
+      db = described_class.database
+      dimension_ids = db.dimensions.flat_map do |d|
+        d.identifiers.map(&:id)
+      end.compact.uniq
+      expect(dimension_ids).to include("NISTd1") # length
+    end
+
+    it "populates quantities with known entities" do
+      db = described_class.database
+      quantity_ids = db.quantities.flat_map do |q|
+        q.identifiers.map(&:id)
+      end.compact.uniq
+      expect(quantity_ids).to include("NISTq1") # length
+    end
+
+    it "populates unit_systems with known entities" do
+      db = described_class.database
+      system_ids = db.unit_systems.flat_map do |s|
+        s.identifiers.map(&:id)
+      end.compact.uniq
+      expect(system_ids).to include("SI_base") # SI
+    end
+
+    it "has non-empty collections" do
+      db = described_class.database
+      expect(db.units).not_to be_empty
+      expect(db.prefixes).not_to be_empty
+      expect(db.dimensions).not_to be_empty
+      expect(db.quantities).not_to be_empty
+      expect(db.unit_systems).not_to be_empty
+    end
+
+    it "caches the database instance" do
+      db1 = described_class.database
+      db2 = described_class.database
+      expect(db1.object_id).to eq(db2.object_id)
+    end
+  end
+
+  describe "YAML file integrity" do
+    let(:data_dir) { described_class.data_dir }
+
+    it "all YAML files have schema_version 2.0.0" do
+      %w[prefixes dimensions units quantities unit_systems].each do |entity|
+        file_path = File.join(data_dir, "#{entity}.yaml")
+        hash = YAML.safe_load_file(file_path)
+        expect(hash["schema_version"]).to eq("2.0.0"),
+                                          "Expected #{entity}.yaml to have schema_version 2.0.0, got #{hash['schema_version']}"
+      end
+    end
+
+    it "all YAML files have their top-level key as an Array" do
+      %w[prefixes dimensions units quantities unit_systems].each do |entity|
+        file_path = File.join(data_dir, "#{entity}.yaml")
+        hash = YAML.safe_load_file(file_path)
+        expect(hash[entity]).to be_a(Array),
+                                "Expected #{entity}.yaml[:#{entity}] to be an Array"
+      end
+    end
+
+    it "units.yaml contains the meter entity" do
+      file_path = File.join(data_dir, "units.yaml")
+      hash = YAML.safe_load_file(file_path)
+      meter = hash["units"].find do |u|
+        u.dig("identifiers", 0, "id") == "NISTu1"
+      end
+      expect(meter).not_to be_nil
+      expect(meter["short"]).to eq("meter")
+    end
+
+    it "prefixes.yaml contains the kilo prefix" do
+      file_path = File.join(data_dir, "prefixes.yaml")
+      hash = YAML.safe_load_file(file_path)
+      kilo = hash["prefixes"].find do |p|
+        p.dig("identifiers", 0, "id") == "NISTp10_3"
+      end
+      expect(kilo).not_to be_nil
+      expect(kilo["short"]).to eq("kilo")
+    end
+
+    it "dimensions.yaml contains the length dimension" do
+      file_path = File.join(data_dir, "dimensions.yaml")
+      hash = YAML.safe_load_file(file_path)
+      length = hash["dimensions"].find do |d|
+        d.dig("identifiers", 0, "id") == "NISTd1"
+      end
+      expect(length).not_to be_nil
+    end
+
+    it "quantities.yaml contains the length quantity" do
+      file_path = File.join(data_dir, "quantities.yaml")
+      hash = YAML.safe_load_file(file_path)
+      length = hash["quantities"].find do |q|
+        q.dig("identifiers", 0, "id") == "NISTq1"
+      end
+      expect(length).not_to be_nil
+    end
+
+    it "unit_systems.yaml contains the SI unit system" do
+      file_path = File.join(data_dir, "unit_systems.yaml")
+      hash = YAML.safe_load_file(file_path)
+      si = hash["unit_systems"].find do |s|
+        s.dig("identifiers", 0, "id") == "SI_base"
+      end
+      expect(si).not_to be_nil
+    end
+
+    it "scales.yaml is a valid YAML file with a top-level key" do
+      file_path = File.join(data_dir, "scales.yaml")
+      hash = YAML.safe_load_file(file_path)
+      expect(hash).to be_a(Hash)
+      expect(hash.keys).not_to be_empty
+    end
+  end
+end
diff --git a/spec/unitsdb/cli_spec.rb b/spec/unitsdb/cli_spec.rb
index d0f0716..8839181 100644
--- a/spec/unitsdb/cli_spec.rb
+++ b/spec/unitsdb/cli_spec.rb
@@ -4,7 +4,7 @@
 require_relative "../../lib/unitsdb/cli"
 require "stringio"
 
-RSpec.describe Unitsdb::CLI do
+RSpec.describe Unitsdb::Cli do
   let(:cli) { described_class.new }
 
   # No global output capture - each test will capture output explicitly
diff --git a/spec/unitsdb/commands/check_si_command_spec.rb b/spec/unitsdb/commands/check_si_command_spec.rb
index a7e8073..21bd451 100644
--- a/spec/unitsdb/commands/check_si_command_spec.rb
+++ b/spec/unitsdb/commands/check_si_command_spec.rb
@@ -9,7 +9,7 @@
   let(:options) { { database: fixture_dir, ttl_dir: ttl_dir } }
   let(:output) { StringIO.new }
   let(:fixture_dir) do
-    File.join(File.dirname(__FILE__), "../../fixtures/unitsdb")
+    File.join(File.dirname(__FILE__), "../../../data")
   end
   let(:ttl_dir) do
     File.join(File.dirname(__FILE__), "../../fixtures/bipm-si-ttl")
diff --git a/spec/unitsdb/commands/get_spec.rb b/spec/unitsdb/commands/get_spec.rb
index 60007cf..d45fb54 100644
--- a/spec/unitsdb/commands/get_spec.rb
+++ b/spec/unitsdb/commands/get_spec.rb
@@ -6,7 +6,7 @@
 RSpec.describe Unitsdb::Commands::Get do
   let(:options) do
     {
-      database: "spec/fixtures/unitsdb",
+      database: "data",
       format: "text",
     }
   end
diff --git a/spec/unitsdb/commands/normalize_spec.rb b/spec/unitsdb/commands/normalize_spec.rb
index f3dc3df..92f9b53 100644
--- a/spec/unitsdb/commands/normalize_spec.rb
+++ b/spec/unitsdb/commands/normalize_spec.rb
@@ -90,27 +90,13 @@
     end
 
     it "handles error for missing input/output without --all" do
-      # Use StringIO to capture output
-      original_stdout = $stdout
-      output = StringIO.new
-      $stdout = output
-
-      # Stub exit to prevent test from actually exiting
-      exit_called = false
-      allow(command).to receive(:exit) { |code|
-        exit_called = true
-        code
-      }
-
-      # Run command with nil input/output
-      command.run(nil, nil)
-
-      # Reset stdout
-      $stdout = original_stdout
-
-      # Verify exit was called and error message was printed
-      expect(exit_called).to be true
-      expect(output.string).to include("Error: INPUT and OUTPUT are required when not using --all")
+      # Run command with nil input/output and expect InvalidParameterError
+      expect do
+        command.run(nil,
+                    nil)
+      end.to raise_error(Unitsdb::Errors::InvalidParameterError) do |error|
+        expect(error.message).to include("INPUT and OUTPUT files are required unless --all flag is specified")
+      end
     end
 
     it "sorts by nist ID when sort option is 'nist'" do
diff --git a/spec/unitsdb/commands/qudt/update_spec.rb b/spec/unitsdb/commands/qudt/update_spec.rb
index b570585..1a6ae20 100644
--- a/spec/unitsdb/commands/qudt/update_spec.rb
+++ b/spec/unitsdb/commands/qudt/update_spec.rb
@@ -7,7 +7,7 @@
 require "unitsdb/commands/qudt/update"
 
 RSpec.describe Unitsdb::Commands::Qudt::Update do
-  let(:database_path) { "spec/fixtures/unitsdb" }
+  let(:database_path) { "data" }
   let(:output_dir) { "tmp/qudt_update_test" }
   let(:options) do
     {
@@ -45,9 +45,11 @@
       invalid_options = options.merge(ttl_dir: "/nonexistent/path")
       command = described_class.new(invalid_options)
 
-      # Should exit with error code 1 for invalid TTL directory
-      expect { command.run }.to raise_error(SystemExit) do |error|
-        expect(error.status).to eq(1)
+      # Should raise FileNotFoundError for invalid TTL directory
+      expect do
+        command.run
+      end.to raise_error(Unitsdb::Errors::FileNotFoundError) do |error|
+        expect(error.message).to include("TTL directory not found")
       end
     end
 
diff --git a/spec/unitsdb/commands/release_spec.rb b/spec/unitsdb/commands/release_spec.rb
index f1301c6..e28411a 100644
--- a/spec/unitsdb/commands/release_spec.rb
+++ b/spec/unitsdb/commands/release_spec.rb
@@ -8,7 +8,7 @@
 require "unitsdb/commands/release"
 
 RSpec.describe Unitsdb::Commands::Release do
-  let(:database_path) { "spec/fixtures/unitsdb" }
+  let(:database_path) { "data" }
   let(:output_dir) { "tmp/release_test" }
   let(:release_version) { "2.0.0" }
   let(:options) do
@@ -138,9 +138,9 @@
           version: release_version }
       end
 
-      it "exits with an error" do
+      it "raises DatabaseLoadError" do
         command = described_class.new(options)
-        expect { command.run }.to raise_error(SystemExit)
+        expect { command.run }.to raise_error(Unitsdb::Errors::DatabaseLoadError)
       end
     end
 
@@ -171,9 +171,9 @@
         FileUtils.rm_rf(temp_db_path)
       end
 
-      it "exits with an error" do
+      it "raises DatabaseLoadError" do
         command = described_class.new(options)
-        expect { command.run }.to raise_error(SystemExit)
+        expect { command.run }.to raise_error(Unitsdb::Errors::DatabaseLoadError)
       end
     end
   end
diff --git a/spec/unitsdb/commands/search_spec.rb b/spec/unitsdb/commands/search_spec.rb
index c1617a6..88569a8 100644
--- a/spec/unitsdb/commands/search_spec.rb
+++ b/spec/unitsdb/commands/search_spec.rb
@@ -5,7 +5,7 @@
 require "fileutils"
 
 RSpec.describe Unitsdb::Commands::Search do
-  let(:fixtures_dir) { File.join("spec", "fixtures", "unitsdb") }
+  let(:fixtures_dir) { "data" }
   let(:command) { described_class.new(options) }
   let(:options) { { database: fixtures_dir } }
 
@@ -139,19 +139,12 @@
           Unitsdb::Errors::DatabaseError, "Test error"
         )
 
-        # Expect exit to be called with status 1
-        expect(command).to receive(:exit).with(1)
-
-        # Redirect stdout to capture output
-        original_stdout = $stdout
-        output = StringIO.new
-        $stdout = output
-
-        # Execute search
-        expect { command.run("test") }.to output(/Test error/).to_stdout
-
-        # Reset stdout
-        $stdout = original_stdout
+        # Expect DatabaseLoadError to be raised with the original error message
+        expect do
+          command.run("test")
+        end.to raise_error(Unitsdb::Errors::DatabaseLoadError) do |error|
+          expect(error.message).to include("Test error")
+        end
       end
     end
   end
diff --git a/spec/unitsdb/commands/ucum/update_spec.rb b/spec/unitsdb/commands/ucum/update_spec.rb
index b3aa909..7e66404 100644
--- a/spec/unitsdb/commands/ucum/update_spec.rb
+++ b/spec/unitsdb/commands/ucum/update_spec.rb
@@ -7,7 +7,7 @@
 require "unitsdb/commands/ucum/update"
 
 RSpec.describe Unitsdb::Commands::Ucum::Update do
-  let(:database_path) { "spec/fixtures/unitsdb" }
+  let(:database_path) { "data" }
   let(:ucum_file) { "spec/fixtures/ucum/ucum-essence.xml" }
   let(:output_dir) { "tmp/ucum_update_test" }
   let(:options) do
diff --git a/spec/unitsdb/commands/validate/identifiers_spec.rb b/spec/unitsdb/commands/validate/identifiers_spec.rb
index 3dd3adf..025cb5d 100644
--- a/spec/unitsdb/commands/validate/identifiers_spec.rb
+++ b/spec/unitsdb/commands/validate/identifiers_spec.rb
@@ -6,7 +6,7 @@
 RSpec.describe Unitsdb::Commands::Validate::Identifiers do
   let(:options) do
     {
-      database: "spec/fixtures/unitsdb",
+      database: "data",
     }
   end
 
diff --git a/spec/unitsdb/commands/validate/qudt_references_spec.rb b/spec/unitsdb/commands/validate/qudt_references_spec.rb
index 7a5635b..c95eef4 100644
--- a/spec/unitsdb/commands/validate/qudt_references_spec.rb
+++ b/spec/unitsdb/commands/validate/qudt_references_spec.rb
@@ -4,7 +4,7 @@
 require "unitsdb/commands/validate/qudt_references"
 
 RSpec.describe Unitsdb::Commands::Validate::QudtReferences do
-  let(:database_path) { "spec/fixtures/unitsdb" }
+  let(:database_path) { "data" }
   let(:options) { { database: database_path } }
 
   describe "#run" do
@@ -29,9 +29,11 @@
       invalid_options = { database: "/nonexistent/path" }
       command = described_class.new(invalid_options)
 
-      # Should exit with error code 1 for invalid database path
-      expect { command.run }.to raise_error(SystemExit) do |error|
-        expect(error.status).to eq(1)
+      # Should raise ValidationError for invalid database path
+      expect do
+        command.run
+      end.to raise_error(Unitsdb::Errors::ValidationError) do |error|
+        expect(error.message).to include("Failed to validate QUDT references")
       end
     end
 
diff --git a/spec/unitsdb/commands/validate/si_references_spec.rb b/spec/unitsdb/commands/validate/si_references_spec.rb
index fda5be4..a09888c 100644
--- a/spec/unitsdb/commands/validate/si_references_spec.rb
+++ b/spec/unitsdb/commands/validate/si_references_spec.rb
@@ -6,7 +6,7 @@
 RSpec.describe Unitsdb::Commands::Validate::SiReferences do
   let(:options) do
     {
-      database: "spec/fixtures/unitsdb",
+      database: "data",
     }
   end
 
diff --git a/spec/unitsdb/commands/validate/ucum_references_spec.rb b/spec/unitsdb/commands/validate/ucum_references_spec.rb
index c3c82b8..e48df65 100644
--- a/spec/unitsdb/commands/validate/ucum_references_spec.rb
+++ b/spec/unitsdb/commands/validate/ucum_references_spec.rb
@@ -4,7 +4,7 @@
 require "unitsdb/commands/validate/ucum_references"
 
 RSpec.describe Unitsdb::Commands::Validate::UcumReferences do
-  let(:database_path) { "spec/fixtures/unitsdb" }
+  let(:database_path) { "data" }
   let(:options) { { database: database_path } }
 
   describe "#run" do
@@ -29,9 +29,11 @@
       invalid_options = { database: "/nonexistent/path" }
       command = described_class.new(invalid_options)
 
-      # Should exit with error code 1 for invalid database path
-      expect { command.run }.to raise_error(SystemExit) do |error|
-        expect(error.status).to eq(1)
+      # Should raise ValidationError for invalid database path
+      expect do
+        command.run
+      end.to raise_error(Unitsdb::Errors::ValidationError) do |error|
+        expect(error.message).to include("Failed to validate UCUM references")
       end
     end
 
diff --git a/spec/unitsdb/database_search_spec.rb b/spec/unitsdb/database_search_spec.rb
index ebab586..a8ab998 100644
--- a/spec/unitsdb/database_search_spec.rb
+++ b/spec/unitsdb/database_search_spec.rb
@@ -3,7 +3,7 @@
 require "spec_helper"
 
 RSpec.describe Unitsdb::Database do
-  let(:fixtures_dir) { File.join("spec", "fixtures", "unitsdb") }
+  let(:fixtures_dir) { "data" }
   let(:database) { described_class.from_db(fixtures_dir) }
 
   describe "search and lookup functionality" do
diff --git a/spec/unitsdb/database_spec.rb b/spec/unitsdb/database_spec.rb
index a1d47fb..103da59 100644
--- a/spec/unitsdb/database_spec.rb
+++ b/spec/unitsdb/database_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Database do
-  dir_path = File.join(__dir__, "../fixtures/unitsdb/")
+  dir_path = File.join(__dir__, "../../data/")
 
   it "parses the full unitsdb database" do
     parsed = described_class.from_db(dir_path)
diff --git a/spec/unitsdb/dimension_spec.rb b/spec/unitsdb/dimension_spec.rb
index 93abc6a..7088ef7 100644
--- a/spec/unitsdb/dimension_spec.rb
+++ b/spec/unitsdb/dimension_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Dimension do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/dimensions.yaml")
+  file_path = File.join(__dir__, "../../data/dimensions.yaml")
   dimensions_yaml = YAML.safe_load_file(file_path)
 
   dimensions_yaml["dimensions"].each do |value|
diff --git a/spec/unitsdb/dimensions_spec.rb b/spec/unitsdb/dimensions_spec.rb
index 6c42aaf..41f70a7 100644
--- a/spec/unitsdb/dimensions_spec.rb
+++ b/spec/unitsdb/dimensions_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Dimensions do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/dimensions.yaml")
+  file_path = File.join(__dir__, "../../data/dimensions.yaml")
 
   it "parses the dimension collection" do
     raw_string = File.read(file_path)
diff --git a/spec/unitsdb/prefix_spec.rb b/spec/unitsdb/prefix_spec.rb
index e08d9c7..93e0716 100644
--- a/spec/unitsdb/prefix_spec.rb
+++ b/spec/unitsdb/prefix_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Prefix do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/prefixes.yaml")
+  file_path = File.join(__dir__, "../../data/prefixes.yaml")
   prefixes_yaml = YAML.safe_load_file(file_path)["prefixes"]
 
   prefixes_yaml.each do |value|
diff --git a/spec/unitsdb/prefixes_spec.rb b/spec/unitsdb/prefixes_spec.rb
index df66dd1..2380b8e 100644
--- a/spec/unitsdb/prefixes_spec.rb
+++ b/spec/unitsdb/prefixes_spec.rb
@@ -3,7 +3,7 @@
 require_relative "../../lib/unitsdb/prefixes"
 
 RSpec.describe Unitsdb::Prefixes do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/prefixes.yaml")
+  file_path = File.join(__dir__, "../../data/prefixes.yaml")
 
   it "parses the prefix collection" do
     raw_string = File.read(file_path)
diff --git a/spec/unitsdb/quantities_spec.rb b/spec/unitsdb/quantities_spec.rb
index fea7b68..0ecc05b 100644
--- a/spec/unitsdb/quantities_spec.rb
+++ b/spec/unitsdb/quantities_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Quantities do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/quantities.yaml")
+  file_path = File.join(__dir__, "../../data/quantities.yaml")
 
   it "parses the quantity collection from the new array structure" do
     raw_string = File.read(file_path)
diff --git a/spec/unitsdb/quantity_spec.rb b/spec/unitsdb/quantity_spec.rb
index fb7043a..d8a8c4c 100644
--- a/spec/unitsdb/quantity_spec.rb
+++ b/spec/unitsdb/quantity_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Quantity do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/quantities.yaml")
+  file_path = File.join(__dir__, "../../data/quantities.yaml")
   quantities_yaml = YAML.safe_load_file(file_path)
 
   quantities_yaml["quantities"].each do |quantity_hash|
diff --git a/spec/unitsdb/scale_spec.rb b/spec/unitsdb/scale_spec.rb
index 41f0fc7..0dcd8ec 100644
--- a/spec/unitsdb/scale_spec.rb
+++ b/spec/unitsdb/scale_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Scale do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/scales.yaml")
+  file_path = File.join(__dir__, "../../data/scales.yaml")
   scales_yaml = YAML.safe_load_file(file_path)
 
   scales_yaml["scales"].each do |scale_hash|
diff --git a/spec/unitsdb/scales_spec.rb b/spec/unitsdb/scales_spec.rb
index cca3e0d..56b7708 100644
--- a/spec/unitsdb/scales_spec.rb
+++ b/spec/unitsdb/scales_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Scales do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/scales.yaml")
+  file_path = File.join(__dir__, "../../data/scales.yaml")
 
   it "parses the scale collection from the new array structure" do
     raw_string = File.read(file_path)
diff --git a/spec/unitsdb/unit_spec.rb b/spec/unitsdb/unit_spec.rb
index 0ea6cdc..232835f 100644
--- a/spec/unitsdb/unit_spec.rb
+++ b/spec/unitsdb/unit_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::Unit do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/units.yaml")
+  file_path = File.join(__dir__, "../../data/units.yaml")
   units_yaml = YAML.safe_load_file(file_path)["units"]
 
   units_yaml.each do |value|
diff --git a/spec/unitsdb/unit_system_spec.rb b/spec/unitsdb/unit_system_spec.rb
index 4f95fa9..3110740 100644
--- a/spec/unitsdb/unit_system_spec.rb
+++ b/spec/unitsdb/unit_system_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe Unitsdb::UnitSystem do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/unit_systems.yaml")
+  file_path = File.join(__dir__, "../../data/unit_systems.yaml")
   unit_systems_yaml = YAML.safe_load_file(file_path)
 
   unit_systems_yaml["unit_systems"].each do |value|
diff --git a/spec/unitsdb/unit_systems_spec.rb b/spec/unitsdb/unit_systems_spec.rb
index d7ca32d..69aed64 100644
--- a/spec/unitsdb/unit_systems_spec.rb
+++ b/spec/unitsdb/unit_systems_spec.rb
@@ -3,7 +3,7 @@
 require_relative "../../lib/unitsdb/unit_systems"
 
 RSpec.describe Unitsdb::UnitSystems do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/unit_systems.yaml")
+  file_path = File.join(__dir__, "../../data/unit_systems.yaml")
 
   it "parses the unit systems collection" do
     raw_string = File.read(file_path)
diff --git a/spec/unitsdb/units_spec.rb b/spec/unitsdb/units_spec.rb
index 11b7e9b..08d3e64 100644
--- a/spec/unitsdb/units_spec.rb
+++ b/spec/unitsdb/units_spec.rb
@@ -3,7 +3,7 @@
 require_relative "../../lib/unitsdb/units"
 
 RSpec.describe Unitsdb::Units do
-  file_path = File.join(__dir__, "../fixtures/unitsdb/units.yaml")
+  file_path = File.join(__dir__, "../../data/units.yaml")
 
   it "parses the unit collection" do
     raw_string = File.read(file_path)
diff --git a/spec/unitsdb/version_compatibility_spec.rb b/spec/unitsdb/version_compatibility_spec.rb
index a8da906..bac61d8 100644
--- a/spec/unitsdb/version_compatibility_spec.rb
+++ b/spec/unitsdb/version_compatibility_spec.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe "UnitsDB 2.0.0 Features" do
-  let(:database_path) { File.join(__dir__, "../fixtures/unitsdb/") }
+  let(:database_path) { File.join(__dir__, "../../data/") }
   let(:db) { Unitsdb::Database.from_db(database_path) }
 
   describe "version validation" do
diff --git a/unitsdb.gemspec b/unitsdb.gemspec
index b31337a..32723fb 100644
--- a/unitsdb.gemspec
+++ b/unitsdb.gemspec
@@ -27,6 +27,8 @@ Gem::Specification.new do |spec|
       f.match(%r{^(test|spec|features)/})
     end
   end
+  # Include YAML data files in the gem
+  spec.files += Dir.glob("data/**/*.yaml")
   spec.bindir = "exe"
   spec.executables = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]