diff --git a/src/components/Json/Json.module.css b/src/components/Json/Json.module.css
index 1646e5c..524284c 100644
--- a/src/components/Json/Json.module.css
+++ b/src/components/Json/Json.module.css
@@ -25,19 +25,26 @@
 
 .clickable {
   cursor: pointer;
-}
 
-.drill {
-  color: #556;
-  font-size: 10pt;
-  margin-left: -12px;
-  margin-right: 4px;
-  padding: 2px 0;
-  user-select: none;
-}
-.clickable:hover .drill {
-  color: #778;
+  /* drill */
+  &::before {
+    content: '▶';
+    color: #556;
+    font-size: 10pt;
+    margin-left: -12px;
+    margin-right: 4px;
+    padding: 2px 0;
+    user-select: none;
+  }
+  &:hover::before {
+    color: #778;
+  }
+  &[aria-expanded="true"]::before {
+    content: '▼';
+  }  
 }
+
+
 .key {
   color: #aad;
   font-weight: bold;
diff --git a/src/components/Json/Json.test.tsx b/src/components/Json/Json.test.tsx
index 3bde428..e7a1c37 100644
--- a/src/components/Json/Json.test.tsx
+++ b/src/components/Json/Json.test.tsx
@@ -27,9 +27,8 @@ describe('Json Component', () => {
     [1, 'foo', null],
     Array.from({ length: 101 }, (_, i) => i),
   ])('collapses any array', (array) => {
-    const { queryByText } = render(<Json json={array} />)
-    expect(queryByText('▶')).toBeTruthy()
-    expect(queryByText('▼')).toBeNull()
+    const { getByRole } = render(<Json json={array} />)
+    expect(getByRole('treeitem').ariaExpanded).toBe('false')
   })
 
   it.for([
@@ -40,13 +39,12 @@ describe('Json Component', () => {
   ])('shows short arrays of primitive items, without trailing comment about length', (array) => {
     const { queryByText } = render(<Json json={array} />)
     expect(queryByText('...')).toBeNull()
-    expect(queryByText('length')).toBeNull()
+    expect(queryByText(/length/)).toBeNull()
   })
 
   it.for([
-    // [1, 'foo', [1, 2, 3]], // TODO(SL): this one does not collapses, what to do? The text is wrong
     Array.from({ length: 101 }, (_, i) => i),
-  ])('hides long arrays, and non-primitive items, with trailing comment about length', (array) => {
+  ])('hides long arrays with trailing comment about length', (array) => {
     const { getByText } = render(<Json json={array} />)
     getByText('...')
     getByText(/length/)
@@ -66,20 +64,39 @@ describe('Json Component', () => {
     getByText('"42"')
   })
 
+  it.for([
+    [1, 'foo', [1, 2, 3]],
+    [1, 'foo', { nested: true }],
+  ])('expands short arrays with non-primitive values', (arr) => {
+    const { getAllByRole } = render(<Json json={arr} />)
+    const treeItems = getAllByRole('treeitem')
+    expect(treeItems.length).toBe(2)
+    expect(treeItems[0]?.getAttribute('aria-expanded')).toBe('true') // the root
+    expect(treeItems[1]?.getAttribute('aria-expanded')).toBe('false') // the non-primitive value (object/array)
+  })
+
   it.for([
     { obj: [314, null] },
     { obj: { nested: true } },
   ])('expands short objects with non-primitive values', (obj) => {
-    const { getByText } = render(<Json json={obj} />)
-    getByText('▼')
+    const { getAllByRole } = render(<Json json={obj} />)
+    const treeItems = getAllByRole('treeitem')
+    expect(treeItems.length).toBe(2)
+    expect(treeItems[0]?.getAttribute('aria-expanded')).toBe('true') // the root
+    expect(treeItems[1]?.getAttribute('aria-expanded')).toBe('false') // the non-primitive value (object/array)
   })
 
   it.for([
     { obj: [314, null] },
     { obj: { nested: true } },
   ])('hides the content and append number of entries when objects with non-primitive values are collapsed', (obj) => {
-    const { getByText } = render(<Json json={obj} />)
-    fireEvent.click(getByText('▼'))
+    const { getAllByRole, getByText } = render(<Json json={obj} />)
+    const root = getAllByRole('treeitem')[0]
+    if (!root) { /* type assertion, getAllByRole would already have thrown */
+      throw new Error('No root element found')
+    }
+    fireEvent.click(root)
+    expect(root.getAttribute('aria-expanded')).toBe('false')
     getByText('...')
     getByText(/entries/)
   })
@@ -90,9 +107,8 @@ describe('Json Component', () => {
     { a: 1, b: true, c: null, d: undefined },
     Object.fromEntries(Array.from({ length: 101 }, (_, i) => [`key${i}`, { nested: true }])),
   ])('collapses long objects, or objects with only primitive values (included empty object)', (obj) => {
-    const { queryByText } = render(<Json json={obj} />)
-    expect(queryByText('▶')).toBeTruthy()
-    expect(queryByText('▼')).toBeNull()
+    const { getByRole } = render(<Json json={obj} />)
+    expect(getByRole('treeitem').getAttribute('aria-expanded')).toBe('false')
   })
 
   it.for([
@@ -105,21 +121,23 @@ describe('Json Component', () => {
 
   it('toggles array collapse state', () => {
     const longArray = Array.from({ length: 101 }, (_, i) => i)
-    const { getByText, queryByText } = render(<Json json={longArray} />)
+    const { getByRole, getByText, queryByText } = render(<Json json={longArray} />)
+    const treeItem = getByRole('treeitem')
     getByText('...')
-    fireEvent.click(getByText('▶'))
+    fireEvent.click(treeItem)
     expect(queryByText('...')).toBeNull()
-    fireEvent.click(getByText('▼'))
+    fireEvent.click(treeItem)
     getByText('...')
   })
 
   it('toggles object collapse state', () => {
     const longObject = Object.fromEntries(Array.from({ length: 101 }, (_, i) => [`key${i}`, { nested: true }]))
-    const { getByText, queryByText } = render(<Json json={longObject} />)
+    const { getByRole, getByText, queryByText } = render(<Json json={longObject} />)
+    const treeItem = getByRole('treeitem') // only one treeitem because the inner objects are collapsed and not represented as treeitems
     getByText('...')
-    fireEvent.click(getByText('▶'))
+    fireEvent.click(treeItem)
     expect(queryByText('...')).toBeNull()
-    fireEvent.click(getByText('▼'))
+    fireEvent.click(treeItem)
     getByText('...')
   })
 })
diff --git a/src/components/Json/Json.tsx b/src/components/Json/Json.tsx
index 20c9657..31f98c6 100644
--- a/src/components/Json/Json.tsx
+++ b/src/components/Json/Json.tsx
@@ -14,7 +14,7 @@ interface JsonProps {
  * JSON viewer component with collapsible objects and arrays.
  */
 export default function Json({ json, label, className }: JsonProps): ReactNode {
-  return <div className={cn(styles.json, className)}>
+  return <div className={cn(styles.json, className)} role="tree">
     <JsonContent json={json} label={label} />
   </div>
 }
@@ -89,19 +89,17 @@ function JsonArray({ array, label }: { array: unknown[], label?: string }): Reac
   const [collapsed, setCollapsed] = useState(shouldObjectCollapse(array))
   const key = label ? <span className={styles.key}>{label}: </span> : ''
   if (collapsed) {
-    return <div className={styles.clickable} onClick={() => { setCollapsed(false) }}>
-      <span className={styles.drill}>{'\u25B6'}</span>
+    return <div role="treeitem" className={styles.clickable} aria-expanded="false" onClick={() => { setCollapsed(false) }}>
       {key}
       <CollapsedArray array={array}></CollapsedArray>
     </div>
   }
   return <>
-    <div className={styles.clickable} onClick={() => { setCollapsed(true) }}>
-      <span className={styles.drill}>{'\u25BC'}</span>
+    <div role="treeitem" className={styles.clickable} aria-expanded="true" onClick={() => { setCollapsed(true) }}>
       {key}
       <span className={styles.array}>{'['}</span>
     </div>
-    <ul>
+    <ul role="group">
       {array.map((item, index) => <li key={index}>{<Json json={item} />}</li>)}
     </ul>
     <div className={styles.array}>{']'}</div>
@@ -154,19 +152,17 @@ function JsonObject({ obj, label }: { obj: object, label?: string }): ReactNode
   const [collapsed, setCollapsed] = useState(shouldObjectCollapse(obj))
   const key = label ? <span className={styles.key}>{label}: </span> : ''
   if (collapsed) {
-    return <div className={styles.clickable} onClick={() => { setCollapsed(false) }}>
-      <span className={styles.drill}>{'\u25B6'}</span>
+    return <div role="treeitem" className={styles.clickable} aria-expanded="false" onClick={() => { setCollapsed(false) }}>
       {key}
       <CollapsedObject obj={obj}></CollapsedObject>
     </div>
   }
   return <>
-    <div className={styles.clickable} onClick={() => { setCollapsed(true) }}>
-      <span className={styles.drill}>{'\u25BC'}</span>
+    <div role="treeitem" className={styles.clickable} aria-expanded="true" onClick={() => { setCollapsed(true) }}>
       {key}
       <span className={styles.object}>{'{'}</span>
     </div>
-    <ul>
+    <ul role="group">
       {Object.entries(obj).map(([key, value]) =>
         <li key={key}>
           <Json json={value as unknown} label={key} />
diff --git a/src/components/JsonView/JsonView.test.tsx b/src/components/JsonView/JsonView.test.tsx
index ae1cf91..2993d8e 100644
--- a/src/components/JsonView/JsonView.test.tsx
+++ b/src/components/JsonView/JsonView.test.tsx
@@ -13,7 +13,7 @@ globalThis.fetch = vi.fn()
 describe('JsonView Component', () => {
   const encoder = new TextEncoder()
 
-  it('renders json content as nested lists (if not collapsed)', async () => {
+  it('renders json content as nested tree items (if not collapsed)', async () => {
     const text = '{"key":["value"]}'
     const body = encoder.encode(text).buffer
     const source: FileSource = {
@@ -29,13 +29,13 @@ describe('JsonView Component', () => {
       text: () => Promise.resolve(text),
     } as Response)
 
-    const { findByRole, findByText } = render(
+    const { findAllByRole, findByText } = render(
       <JsonView source={source} setError={console.error} />
     )
 
     expect(fetch).toHaveBeenCalledWith('testKey0', undefined)
     // Wait for asynchronous JSON loading and parsing
-    await findByRole('list')
+    await findAllByRole('treeitem')
     await findByText('key:')
     await findByText('"value"')
   })