From e8ff6a8a619f3533a1d1ef0b9017e418411d28a2 Mon Sep 17 00:00:00 2001
From: Tarek Lokal <tarek@example.com>
Date: Sat, 11 Jul 2026 12:44:30 +0200
Subject: [PATCH] feat: filter appendix licenses by rule attributes (#637)

Interactive filter panel matches licenses that satisfy every selected
permission, condition, or limitation. Table rows carry data-rules tags.

Co-authored-by: Cursor <cursoragent@cursor.com>
---
 _includes/appendix-filter.html | 25 ++++++++++++++++
 _includes/css/responsive.css   | 45 +++++++++++++++++++++++++++++
 appendix.md                    | 15 ++++++++--
 assets/js/appendix-filter.js   | 52 ++++++++++++++++++++++++++++++++++
 4 files changed, 135 insertions(+), 2 deletions(-)
 create mode 100644 _includes/appendix-filter.html
 create mode 100644 assets/js/appendix-filter.js

diff --git a/_includes/appendix-filter.html b/_includes/appendix-filter.html
new file mode 100644
index 000000000..5f9755a4e
--- /dev/null
+++ b/_includes/appendix-filter.html
@@ -0,0 +1,25 @@
+<div id="appendix-filter" class="appendix-filter" aria-label="Filter licenses by rules">
+  <p><strong>Filter by rules</strong> — show only licenses that match <em>every</em> selected attribute:</p>
+  <div class="appendix-filter-groups">
+    {% assign types = "permissions|conditions|limitations" | split: "|" %}
+    {% assign seen_tags = '' %}
+    {% for type in types %}
+      <fieldset class="appendix-filter-group">
+        <legend>{{ type | capitalize }}</legend>
+        {% assign rules = site.data.rules[type] | sort: "label" %}
+        {% for rule_obj in rules %}
+          {% if seen_tags contains rule_obj.tag or rule_obj.tag contains '--' %}
+            {% continue %}
+          {% endif %}
+          {% capture seen_tags %}{{ seen_tags | append:rule_obj.tag }}{% endcapture %}
+          <label class="appendix-filter-chip">
+            <input type="checkbox" value="{{ rule_obj.tag }}" data-rule-type="{{ type }}" />
+            {{ rule_obj.label }}
+          </label>
+        {% endfor %}
+      </fieldset>
+    {% endfor %}
+  </div>
+  <button type="button" id="appendix-filter-clear" class="appendix-filter-clear">Clear filters</button>
+  <p id="appendix-filter-status" class="appendix-filter-status" aria-live="polite"></p>
+</div>
diff --git a/_includes/css/responsive.css b/_includes/css/responsive.css
index 64524f36b..a79da24b7 100644
--- a/_includes/css/responsive.css
+++ b/_includes/css/responsive.css
@@ -164,6 +164,51 @@
   }
 }
 
+.appendix-table-wrapper {
+  overflow-x: auto;
+  max-width: 100%;
+  margin-bottom: 2rem;
+}
+
+.appendix-filter {
+  margin: 1.5rem 0;
+  padding: 1rem;
+  border: 1px solid #ddd;
+  border-radius: 6px;
+  background: color-mix(in srgb, var(--backgroundColor) 92%, #149ad4 8%);
+}
+
+.appendix-filter-groups {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 1rem;
+}
+
+.appendix-filter-group {
+  border: none;
+  margin: 0;
+  padding: 0;
+  min-width: 12rem;
+}
+
+.appendix-filter-chip {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.35rem;
+  margin: 0.15rem 0.5rem 0.15rem 0;
+  font-size: 0.85rem;
+  font-weight: normal;
+}
+
+.appendix-filter-clear {
+  margin-top: 0.75rem;
+}
+
+.appendix-filter-status {
+  margin: 0.5rem 0 0;
+  font-size: 0.85rem;
+}
+
 /* Smartphones (portrait) ----------- */
 @media only screen and (max-width : 321px) {
   .container {
diff --git a/appendix.md b/appendix.md
index 62c119d98..cf421dd33 100644
--- a/appendix.md
+++ b/appendix.md
@@ -9,8 +9,12 @@ For reference, here is a table of every license described in the [choosealicense
 
 If you're here to choose a license, **[start from the home page](/)** to see a few licenses that will work for most cases.
 
-<table border style="font-size: xx-small; position: relative">
+{% include appendix-filter.html %}
+
+<div class="appendix-table-wrapper">
+<table class="appendix-table" border style="font-size: xx-small; position: relative">
 {% assign types = "permissions|conditions|limitations" | split: "|" %}
+<thead>
 <tr style="position: sticky; top: 0; z-index: 1000001; background: color-mix(in srgb, var(--backgroundColor) 70%, transparent);">
   <th scope="col" style="text-align: center">License</th>
   {% assign seen_tags = '' %}
@@ -25,9 +29,12 @@ If you're here to choose a license, **[start from the home page](/)** to see a f
     {% endfor %}
   {% endfor %}
 </tr>
+</thead>
+<tbody>
 {% assign licenses = site.licenses | sort: "path" %}
 {% for license in licenses %}
-  <tr style="height: 3em"><th scope="row"><a href="{{ license.id }}">{{ license.title }}</a></th>
+  {% capture rule_tags %}{% for t in types %}{% for r in license[t] %}{{ r }},{% endfor %}{% endfor %}{% endcapture %}
+  <tr style="height: 3em" data-rules="{{ rule_tags | strip }}"><th scope="row"><a href="{{ license.url }}">{{ license.title }}</a></th>
   {% assign seen_tags = '' %}
   {% for type in types %}
     {% assign rules = site.data.rules[type] | sort: "label" %}
@@ -62,7 +69,9 @@ If you're here to choose a license, **[start from the home page](/)** to see a f
   {% endfor %}
   </tr>
 {% endfor %}
+</tbody>
 </table>
+</div>
 
 ## Legend
 
@@ -93,3 +102,5 @@ If you're here to choose a license, **[start from the home page](/)** to see a f
   {% endfor %}
   </dl>
 {% endfor %}
+
+<script src="{{ '/assets/js/appendix-filter.js' | relative_url }}"></script>
diff --git a/assets/js/appendix-filter.js b/assets/js/appendix-filter.js
new file mode 100644
index 000000000..9de502520
--- /dev/null
+++ b/assets/js/appendix-filter.js
@@ -0,0 +1,52 @@
+class AppendixFilter {
+  constructor(root) {
+    this.root = root;
+    this.table = document.querySelector('.appendix-table');
+    this.rows = Array.from(this.table?.querySelectorAll('tbody tr') || []);
+    this.checkboxes = Array.from(root.querySelectorAll('input[type="checkbox"]'));
+    this.statusEl = document.querySelector('#appendix-filter-status');
+    this.clearBtn = document.querySelector('#appendix-filter-clear');
+
+    this.checkboxes.forEach((cb) => cb.addEventListener('change', () => this.apply()));
+    this.clearBtn?.addEventListener('click', () => {
+      this.checkboxes.forEach((cb) => { cb.checked = false; });
+      this.apply();
+    });
+
+    this.apply();
+  }
+
+  selectedRules() {
+    return this.checkboxes.filter((cb) => cb.checked).map((cb) => cb.value);
+  }
+
+  rowMatches(row, rules) {
+    if (!rules.length) return true;
+    const rowTags = (row.dataset.rules || '').split(',').filter(Boolean);
+    return rules.every((rule) => rowTags.includes(rule));
+  }
+
+  apply() {
+    const rules = this.selectedRules();
+    let visible = 0;
+
+    this.rows.forEach((row) => {
+      const match = this.rowMatches(row, rules);
+      row.hidden = !match;
+      if (match) visible += 1;
+    });
+
+    if (this.statusEl) {
+      if (!rules.length) {
+        this.statusEl.textContent = `Showing all ${this.rows.length} licenses.`;
+      } else {
+        this.statusEl.textContent = `Showing ${visible} of ${this.rows.length} licenses matching ${rules.length} selected rule(s).`;
+      }
+    }
+  }
+}
+
+document.addEventListener('DOMContentLoaded', () => {
+  const root = document.querySelector('#appendix-filter');
+  if (root) new AppendixFilter(root);
+});