diff --git a/src/components/Json/Json.module.css b/src/components/Json/Json.module.css
index 5a53d94f..59fae5d7 100644
--- a/src/components/Json/Json.module.css
+++ b/src/components/Json/Json.module.css
@@ -52,3 +52,9 @@
 .string {
   color: #eaa;
 }
+.other {
+  color: #d6d6d6;
+}
+.comment {
+  color: #ccd8;
+}
diff --git a/src/components/Json/Json.stories.tsx b/src/components/Json/Json.stories.tsx
new file mode 100644
index 00000000..7f959e5f
--- /dev/null
+++ b/src/components/Json/Json.stories.tsx
@@ -0,0 +1,73 @@
+import type { Meta, StoryObj } from '@storybook/react'
+import type { ComponentProps } from 'react'
+import Json from './Json.js'
+
+const meta: Meta<typeof Json> = {
+  component: Json,
+}
+export default meta
+type Story = StoryObj<typeof Json>;
+
+function render(args: ComponentProps<typeof Json>) {
+  return (
+    <div style={{ padding: '2rem', backgroundColor: '#22222b' }}>
+      <Json {...args} />
+    </div>
+  )
+}
+
+export const Default: Story = {
+  args: {
+    json: {
+      a: 1,
+      b: 'hello',
+      c: [1, 2, 3],
+      d: { e: 4, f: 5 },
+      e: null,
+      f: undefined,
+      g: true,
+      // h: 123456n, // commented because it breaks storybook...
+    },
+    label: 'json',
+  },
+  render,
+}
+
+export const Arrays: Story = {
+  args: {
+    json: {
+      empty: [],
+      numbers1: Array.from({ length: 1 }, (_, i) => i),
+      numbers8: Array.from({ length: 8 }, (_, i) => i),
+      numbers100: Array.from({ length: 100 }, (_, i) => i),
+      strings2: Array.from({ length: 2 }, (_, i) => `hello ${i}`),
+      strings8: Array.from({ length: 8 }, (_, i) => `hello ${i}`),
+      strings100: Array.from({ length: 100 }, (_, i) => `hello ${i}`),
+      misc: Array.from({ length: 8 }, (_, i) => i % 2 ? `hello ${i}` : i),
+      misc2: Array.from({ length: 8 }, (_, i) => i % 3 === 0 ? i : i % 3 === 1 ? `hello ${i}` : [i, i + 1, i + 2]),
+      misc3: [1, 'hello', null, undefined],
+      arrays100: Array.from({ length: 100 }, (_, i) => [i, i + 1, i + 2]),
+    },
+    label: 'json',
+  },
+  render,
+}
+
+export const Objects: Story = {
+  args: {
+    json: {
+      empty: {},
+      numbers1: { k0: 1 },
+      numbers8: Object.fromEntries(Array.from({ length: 8 }, (_, i) => [`k${i}`, i])),
+      numbers100: Object.fromEntries(Array.from({ length: 100 }, (_, i) => [`k${i}`, i])),
+      strings8: Object.fromEntries(Array.from({ length: 8 }, (_, i) => [`k${i}`, `hello ${i}`])),
+      strings100: Object.fromEntries(Array.from({ length: 100 }, (_, i) => [`k${i}`, `hello ${i}`])),
+      misc: Object.fromEntries(Array.from({ length: 8 }, (_, i) => [`k${i}`, i % 2 ? `hello ${i}` : i])),
+      misc2: Object.fromEntries(Array.from({ length: 8 }, (_, i) => [`k${i}`, i % 3 === 0 ? i : i % 3 === 1 ? `hello ${i}` : [i, i + 1, i + 2]])),
+      misc3: { k0: 1, k1: 'a', k2: null, k3: undefined },
+      arrays100: Object.fromEntries(Array.from({ length: 100 }, (_, i) => [`k${i}`, [i, i + 1, i + 2]])),
+    },
+    label: 'json',
+  },
+  render,
+}
diff --git a/src/components/Json/Json.test.tsx b/src/components/Json/Json.test.tsx
index 3b495eaa..dd460973 100644
--- a/src/components/Json/Json.test.tsx
+++ b/src/components/Json/Json.test.tsx
@@ -1,6 +1,7 @@
 import { fireEvent, render } from '@testing-library/react'
 import { describe, expect, it } from 'vitest'
 import Json from './Json.js'
+import { isPrimitive, shouldObjectCollapse } from './helpers.js'
 
 describe('Json Component', () => {
   it('renders primitive types correctly', () => {
@@ -19,6 +20,38 @@ describe('Json Component', () => {
     expect(getByText('"bar"')).toBeDefined()
   })
 
+  it.for([
+    ['foo', 'bar'],
+    [],
+    [1, 2, 3],
+    [1, 'foo', null],
+    Array.from({ length: 101 }, (_, i) => i),
+  ])('collapses any array', (array) => {
+    const { queryByText } = render(<Json json={array} />)
+    expect(queryByText('▶')).toBeDefined()
+    expect(queryByText('▼')).toBeNull()
+  })
+
+  it.for([
+    ['foo', 'bar'],
+    [],
+    [1, 2, 3],
+    [1, 'foo', null, undefined],
+  ])('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()
+  })
+
+  it.for([
+    [1, 'foo', [1, 2, 3]],
+    Array.from({ length: 101 }, (_, i) => i),
+  ])('hides long arrays, and non-primitive items, with trailing comment about length', (array) => {
+    const { queryByText } = render(<Json json={array} />)
+    expect(queryByText('...')).toBeDefined()
+    expect(queryByText('length')).toBeDefined()
+  })
+
   it('renders an object', () => {
     const { getByText } = render(<Json json={{ key: 'value' }} />)
     expect(getByText('key:')).toBeDefined()
@@ -26,32 +59,95 @@ describe('Json Component', () => {
   })
 
   it('renders nested objects', () => {
-    const { getByText } = render(<Json json={{ obj: { arr: [314, null] } }} />)
+    const { getByText } = render(<Json json={{ obj: { arr: [314, '42'] } }} />)
     expect(getByText('obj:')).toBeDefined()
     expect(getByText('arr:')).toBeDefined()
     expect(getByText('314')).toBeDefined()
-    expect(getByText('null')).toBeDefined()
+    expect(getByText('"42"')).toBeDefined()
+  })
+
+  it.for([
+    { obj: [314, null] },
+    { obj: { nested: true } },
+  ])('expands short objects with non-primitive values', (obj) => {
+    const { queryByText } = render(<Json json={obj} />)
+    expect(queryByText('▼')).toBeDefined()
+  })
+
+  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, queryByText } = render(<Json json={obj} />)
+    fireEvent.click(getByText('▼'))
+    expect(queryByText('...')).toBeDefined()
+    expect(queryByText('entries')).toBeDefined()
+  })
+
+  it.for([
+    {},
+    { a: 1, b: 2 },
+    { a: 1, b: true, c: null, d: undefined },
+    Object.fromEntries(Array.from({ length: 101 }, (_, i) => [`key${i}`, { nested: true }])),
+  ])('collapses long objects, or objects with only primitive values (included empty object)', (obj) => {
+    const { queryByText } = render(<Json json={obj} />)
+    expect(queryByText('▶')).toBeDefined()
+    expect(queryByText('▼')).toBeNull()
+  })
+
+  it.for([
+    Object.fromEntries(Array.from({ length: 101 }, (_, i) => [`key${i}`, { nested: true }])),
+  ])('hides the content and append number of entries when objects has many entries', (obj) => {
+    const { queryByText } = render(<Json json={obj} />)
+    expect(queryByText('...')).toBeDefined()
+    expect(queryByText('entries')).toBeDefined()
   })
 
   it('toggles array collapse state', () => {
-    const { getByText, queryByText } = render(<Json json={['foo', 'bar']} />)
-    expect(getByText('"foo"')).toBeDefined()
-    expect(getByText('"bar"')).toBeDefined()
+    const longArray = Array.from({ length: 101 }, (_, i) => i)
+    const { getByText, queryByText } = render(<Json json={longArray} />)
+    expect(getByText('...')).toBeDefined()
+    fireEvent.click(getByText('▶'))
+    expect(queryByText('...')).toBeNull()
     fireEvent.click(getByText('▼'))
-    expect(queryByText('0: 1')).toBeNull()
-    fireEvent.click(getByText('[...]'))
-    expect(getByText('"foo"')).toBeDefined()
-    expect(getByText('"bar"')).toBeDefined()
+    expect(getByText('...')).toBeDefined()
   })
 
   it('toggles object collapse state', () => {
-    const { getByText, queryByText } = render(<Json json={{ key: 'value' }} />)
-    expect(getByText('key:')).toBeDefined()
-    expect(getByText('"value"')).toBeDefined()
+    const longObject = Object.fromEntries(Array.from({ length: 101 }, (_, i) => [`key${i}`, { nested: true }]))
+    const { getByText, queryByText } = render(<Json json={longObject} />)
+    expect(getByText('...')).toBeDefined()
+    fireEvent.click(getByText('▶'))
+    expect(queryByText('...')).toBeNull()
     fireEvent.click(getByText('▼'))
-    expect(queryByText('key: "value"')).toBeNull()
-    fireEvent.click(getByText('{...}'))
-    expect(getByText('key:')).toBeDefined()
-    expect(getByText('"value"')).toBeDefined()
+    expect(getByText('...')).toBeDefined()
+  })
+})
+
+describe('isPrimitive', () => {
+  it('returns true only for primitive types', () => {
+    expect(isPrimitive('test')).toBe(true)
+    expect(isPrimitive(42)).toBe(true)
+    expect(isPrimitive(true)).toBe(true)
+    expect(isPrimitive(1n)).toBe(true)
+    expect(isPrimitive(null)).toBe(true)
+    expect(isPrimitive(undefined)).toBe(true)
+    expect(isPrimitive({})).toBe(false)
+    expect(isPrimitive([])).toBe(false)
+  })
+})
+
+describe('shouldObjectCollapse', () => {
+  it('returns true for objects with all primitive values', () => {
+    expect(shouldObjectCollapse({ a: 1, b: 'test' })).toBe(true)
+  })
+
+  it('returns false for objects with non-primitive values', () => {
+    expect(shouldObjectCollapse({ a: 1, b: {} })).toBe(false)
+  })
+
+  it('returns true for large objects', () => {
+    const largeObject = Object.fromEntries(Array.from({ length: 101 }, (_, i) => [`key${i}`, i]))
+    expect(shouldObjectCollapse(largeObject)).toBe(true)
   })
 })
diff --git a/src/components/Json/Json.tsx b/src/components/Json/Json.tsx
index 27887808..66bbbc73 100644
--- a/src/components/Json/Json.tsx
+++ b/src/components/Json/Json.tsx
@@ -1,5 +1,6 @@
 import { ReactNode, useState } from 'react'
 import styles from './Json.module.css'
+import { isPrimitive, shouldObjectCollapse } from './helpers.js'
 
 interface JsonProps {
   json: unknown
@@ -10,6 +11,10 @@ interface JsonProps {
  * JSON viewer component with collapsible objects and arrays.
  */
 export default function Json({ json, label }: JsonProps): ReactNode {
+  return <div className={styles.json}><JsonContent json={json} label={label} /></div>
+}
+
+function JsonContent({ json, label }: JsonProps): ReactNode {
   let div
   if (Array.isArray(json)) {
     div = <JsonArray array={json} label={label} />
@@ -24,22 +29,66 @@ export default function Json({ json, label }: JsonProps): ReactNode {
       div = <>{key}<span className={styles.number}>{JSON.stringify(json)}</span></>
     } else if (typeof json === 'bigint') {
       // it's not really json, but show it anyway
-      div = <>{key}<span>{json.toString()}</span></>
+      div = <>{key}<span className={styles.number}>{json.toString()}</span></>
+    } else if (json === undefined) {
+      // it's not json
+      div = <>{key}<span className={styles.other}>undefined</span></>
     } else {
-      div = <>{key}<span>{JSON.stringify(json)}</span></>
+      div = <>{key}<span className={styles.other}>{JSON.stringify(json)}</span></>
+    }
+  }
+  return div
+}
+
+function CollapsedArray({ array }: {array: unknown[]}): ReactNode {
+  // the character count is approximate, but it should be enough
+  // to avoid showing too many entries
+  const maxCharacterCount = 40
+  const separator = ', '
+
+  const children: ReactNode[] = []
+  let suffix: string | undefined = undefined
+
+  let characterCount = 0
+  for (const [index, value] of array.entries()) {
+    if (index > 0) {
+      characterCount += separator.length
+      children.push(<span key={`separator-${index - 1}`}>{separator}</span>)
+    }
+    // should we continue?
+    if (isPrimitive(value)) {
+      const asString = typeof value === 'bigint' ? value.toString() :
+        value === undefined ? 'undefined' /* see JsonContent - even if JSON.stringify([undefined]) === '[null]' */:
+          JSON.stringify(value)
+      characterCount += asString.length
+      if (characterCount < maxCharacterCount) {
+        children.push(<JsonContent json={value} key={`value-${index}`} />)
+        continue
+      }
     }
+    // no: it was the last entry
+    children.push(<span key="rest">...</span>)
+    suffix = ` length: ${array.length}`
+    break
   }
-  return <div className={styles.json}>{div}</div>
+  return (
+    <>
+      <span className={styles.array}>{'['}</span>
+      <span className={styles.array}>{children}</span>
+      <span className={styles.array}>{']'}</span>
+      {suffix && <span className={styles.comment}>{suffix}</span>}
+    </>
+  )
 }
 
 function JsonArray({ array, label }: { array: unknown[], label?: string }): ReactNode {
-  const [collapsed, setCollapsed] = useState(false)
+  const [collapsed, setCollapsed] = useState(true)
   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>
       {key}
-      <span className={styles.array}>{'[...]'}</span>
+      <CollapsedArray array={array}></CollapsedArray>
     </div>
   }
   return <>
@@ -55,14 +104,57 @@ function JsonArray({ array, label }: { array: unknown[], label?: string }): Reac
   </>
 }
 
+function CollapsedObject({ obj }: {obj: object}): ReactNode {
+  // the character count is approximate, but it should be enough
+  // to avoid showing too many entries
+  const maxCharacterCount = 40
+  const separator = ', '
+  const kvSeparator = ': '
+
+  const children: ReactNode[] = []
+  let suffix: string | undefined = undefined
+
+  const entries = Object.entries(obj)
+  let characterCount = 0
+  for (const [index, [key, value]] of entries.entries()) {
+    if (index > 0) {
+      characterCount += separator.length
+      children.push(<span key={`separator-${index - 1}`}>{separator}</span>)
+    }
+    // should we continue?
+    if (isPrimitive(value)) {
+      const asString = typeof value === 'bigint' ? value.toString() :
+        value === undefined ? 'undefined' /* see JsonContent - even if JSON.stringify([undefined]) === '[null]' */:
+          JSON.stringify(value)
+      characterCount += key.length + kvSeparator.length + asString.length
+      if (characterCount < maxCharacterCount) {
+        children.push(<JsonContent json={value as unknown} label={key} key={`value-${index}`} />)
+        continue
+      }
+    }
+    // no: it was the last entry
+    children.push(<span key="rest">...</span>)
+    suffix = ` entries: ${entries.length}`
+    break
+  }
+  return (
+    <>
+      <span className={styles.object}>{'{'}</span>
+      <span className={styles.object}>{children}</span>
+      <span className={styles.object}>{'}'}</span>
+      {suffix && <span className={styles.comment}>{suffix}</span>}
+    </>
+  )
+}
+
 function JsonObject({ obj, label }: { obj: object, label?: string }): ReactNode {
-  const [collapsed, setCollapsed] = useState(false)
+  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>
       {key}
-      <span className={styles.object}>{'{...}'}</span>
+      <CollapsedObject obj={obj}></CollapsedObject>
     </div>
   }
   return <>
diff --git a/src/components/Json/helpers.ts b/src/components/Json/helpers.ts
new file mode 100644
index 00000000..62beeb07
--- /dev/null
+++ b/src/components/Json/helpers.ts
@@ -0,0 +1,22 @@
+export function isPrimitive(value: unknown): boolean {
+  return (
+    value === undefined ||
+    value === null ||
+    !Array.isArray(value) &&
+    typeof value !== 'object' &&
+    typeof value !== 'function'
+  )
+}
+
+export function shouldObjectCollapse(obj: object): boolean {
+  const values = Object.values(obj)
+  if (
+    // if all the values are primitive
+    values.every(value => isPrimitive(value))
+      // if the object has too many entries
+      || values.length >= 100
+  ) {
+    return true
+  }
+  return false
+}
diff --git a/src/components/JsonView/JsonView.test.tsx b/src/components/JsonView/JsonView.test.tsx
index 15248510..45974c29 100644
--- a/src/components/JsonView/JsonView.test.tsx
+++ b/src/components/JsonView/JsonView.test.tsx
@@ -13,8 +13,9 @@ globalThis.fetch = vi.fn()
 describe('JsonView Component', () => {
   const encoder = new TextEncoder()
 
-  it('renders json content as nested lists', async () => {
-    const body = encoder.encode('{"key":"value"}').buffer as ArrayBuffer
+  it('renders json content as nested lists (if not collapsed)', async () => {
+    const text = '{"key":["value"]}'
+    const body = encoder.encode(text).buffer as ArrayBuffer
     const source: FileSource = {
       resolveUrl: 'testKey0',
       kind: 'file',
@@ -25,7 +26,7 @@ describe('JsonView Component', () => {
     vi.mocked(fetch).mockResolvedValueOnce({
       status: 200,
       headers: new Headers({ 'Content-Length': body.byteLength.toString() }),
-      text: () => Promise.resolve('{"key":"value"}'),
+      text: () => Promise.resolve(text),
     } as Response)
 
     const { findByRole, findByText } = render(