diff --git a/mobile/src/session/MobileNativeChatMessage.test.ts b/mobile/src/session/MobileNativeChatMessage.test.ts
index bb687b77ba6..f38a437d55c 100644
--- a/mobile/src/session/MobileNativeChatMessage.test.ts
+++ b/mobile/src/session/MobileNativeChatMessage.test.ts
@@ -1,7 +1,8 @@
 import { createElement } from 'react'
-import { act, create, type ReactTestRenderer } from 'react-test-renderer'
+import { act, create, type ReactTestInstance, type ReactTestRenderer } from 'react-test-renderer'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import type { NativeChatMessage } from '../../../src/shared/native-chat-types'
+import { MAX_TOOL_RESULT_CHARS } from './mobile-native-chat-message-styles'
 
 vi.mock('react-native', async () => {
   const React = await import('react')
@@ -30,7 +31,11 @@ function userMessage(blocks: NativeChatMessage['blocks']): NativeChatMessage {
   return { id: 'u1', role: 'user', blocks, timestamp: null, source: 'transcript' }
 }
 
-describe('MobileNativeChatMessage image-ref rendering', () => {
+function toolMessage(blocks: NativeChatMessage['blocks']): NativeChatMessage {
+  return { id: 'a1', role: 'assistant', blocks, timestamp: null, source: 'transcript' }
+}
+
+describe('MobileNativeChatMessage', () => {
   let renderer: ReactTestRenderer | null = null
 
   beforeEach(() => {
@@ -41,7 +46,10 @@ describe('MobileNativeChatMessage image-ref rendering', () => {
     renderer = null
   })
 
-  function render(message: NativeChatMessage): ReactTestRenderer {
+  function render(
+    message: NativeChatMessage,
+    props: { toolsExpanded?: boolean } = {}
+  ): ReactTestRenderer {
     const original = console.error
     const spy = vi.spyOn(console, 'error').mockImplementation((...a) => {
       if (typeof a[0] === 'string' && a[0].includes('react-test-renderer is deprecated')) {
@@ -51,7 +59,7 @@ describe('MobileNativeChatMessage image-ref rendering', () => {
     })
     try {
       act(() => {
-        renderer = create(createElement(MobileNativeChatMessage, { message }))
+        renderer = create(createElement(MobileNativeChatMessage, { message, ...props }))
       })
     } finally {
       spy.mockRestore()
@@ -59,6 +67,9 @@ describe('MobileNativeChatMessage image-ref rendering', () => {
     return renderer!
   }
 
+  const textIn = (node: ReactTestInstance): string[] =>
+    node.findAllByType('Text' as never).map((text) => String(text.children.join('')))
+
   it('renders a loadable preview URI as an image thumbnail', () => {
     const tree = render(userMessage([{ type: 'image-ref', url: 'file:///a.jpg', alt: 'a photo' }]))
     const image = tree.root.findByType('Image' as never)
@@ -84,4 +95,50 @@ describe('MobileNativeChatMessage image-ref rendering', () => {
       .map((node) => String(node.children.join('')))
     expect(texts.some((text) => text.includes('/tmp/host.png'))).toBe(true)
   })
+
+  it('labels a tool row with the target path instead of raw input JSON', () => {
+    const tree = render(
+      toolMessage([{ type: 'tool-call', name: 'Read', input: { file_path: 'src/index.ts' } }]),
+      { toolsExpanded: true }
+    )
+    const texts = textIn(tree.root)
+    expect(texts).toContain('src/index.ts')
+    expect(texts.some((text) => text.includes('"file_path":"src/index.ts"'))).toBe(false)
+  })
+
+  it('bounds expanded diff-less tool input before native text layout', () => {
+    const tree = render(
+      toolMessage([
+        { type: 'tool-call', name: 'CustomTool', input: { payload: 'x'.repeat(100_000) } }
+      ]),
+      { toolsExpanded: true }
+    )
+    const detail = textIn(tree.root).find((text) => text.startsWith('{\n'))
+    expect(detail).toHaveLength(MAX_TOOL_RESULT_CHARS + 1)
+    expect(detail?.endsWith('…')).toBe(true)
+  })
+
+  it('expands formatted detail for a collapsed JSON-string tool input', () => {
+    const tree = render(
+      toolMessage([
+        {
+          type: 'tool-call',
+          name: 'CustomTool',
+          input: '{"cmd":"git status","description":"Inspect changes"}'
+        }
+      ])
+    )
+    const pressableWith = (label: string): ReactTestInstance =>
+      tree.root.findAllByType('Pressable' as never).find((node) => textIn(node).includes(label))!
+
+    act(() => pressableWith('1×').props.onPress())
+    // The row label is the command, and the detail stays closed until tapped.
+    expect(textIn(tree.root)).toContain('git status')
+    expect(textIn(tree.root).some((text) => text.startsWith('{\n'))).toBe(false)
+
+    act(() => pressableWith('CustomTool').props.onPress())
+    expect(textIn(tree.root)).toContain(
+      '{\n  "cmd": "git status",\n  "description": "Inspect changes"\n}'
+    )
+  })
 })
diff --git a/mobile/src/session/MobileNativeChatMessage.tsx b/mobile/src/session/MobileNativeChatMessage.tsx
index d8458f1b889..6efd4069959 100644
--- a/mobile/src/session/MobileNativeChatMessage.tsx
+++ b/mobile/src/session/MobileNativeChatMessage.tsx
@@ -17,7 +17,9 @@ import { isRenderableImageUri } from './mobile-native-chat-image-preview'
 import { MAX_TOOL_RESULT_CHARS, styles, TEXT_SIZE } from './mobile-native-chat-message-styles'
 import { nativeChatMessageText } from './mobile-native-chat-message-text'
 import {
-  summarizeToolInput,
+  describeToolInput,
+  formatToolInput,
+  isStructuredToolInput,
   summarizeToolRun,
   toolFilePath
 } from './mobile-native-chat-tool-summary'
@@ -46,6 +48,12 @@ function DiffView({ lines }: { lines: DiffLine[] }): React.JSX.Element {
   )
 }
 
+/** Cap a mono block at the same size as desktop's tool detail — native text
+ *  layout has no scroll container to absorb a runaway payload. */
+function boundedText(text: string): string {
+  return text.length > MAX_TOOL_RESULT_CHARS ? `${text.slice(0, MAX_TOOL_RESULT_CHARS)}…` : text
+}
+
 /** A single inline tool line — `▸ ToolName  preview` — that expands in place to
  *  show the call's diff/input or the result's body. Mirrors the reference design
  *  where tool calls read as flat lines in the conversation, not boxed blocks. */
@@ -63,11 +71,7 @@ function ResultBody({
   }
   return (
     <View style={[styles.toolResult, isError && styles.toolResultError]}>
-      <Text style={styles.mono}>
-        {output.length > MAX_TOOL_RESULT_CHARS
-          ? `${output.slice(0, MAX_TOOL_RESULT_CHARS)}…`
-          : output}
-      </Text>
+      <Text style={styles.mono}>{boundedText(output)}</Text>
     </View>
   )
 }
@@ -88,14 +92,23 @@ function ToolLine({
   const [expanded, setExpanded] = useState(defaultExpanded)
   const { call, result } = pair
   const name = call ? call.name : 'Result'
+  // The row label is a human summary (path / primary arg), never raw JSON; the
+  // expanded detail below carries the full formatted input.
   const preview = call
-    ? summarizeToolInput(call.input)
+    ? describeToolInput(call.input)
     : (result?.output.split('\n')[0]?.slice(0, 80) ?? '')
   // Why: collapsed tool rows are the common path; defer bounded diff parsing
-  // until the user asks to reveal the detail.
+  // and detail formatting until the user asks to reveal the detail.
   const callDiff = expanded && call ? diffFromToolCall(call.name, call.input, diffLineLimit) : null
   const resultDiff = expanded && result ? diffFromText(result.output, diffLineLimit) : null
-  const hasDetail = callDiff !== null || result !== undefined || preview.length > 40
+  // Bound before handing it to native text layout, like the result body.
+  const callDetail =
+    expanded && call && !callDiff ? boundedText(formatToolInput(call.input)) : undefined
+  const hasDetail =
+    callDiff !== null ||
+    result !== undefined ||
+    preview.length > 40 ||
+    (call !== undefined && isStructuredToolInput(call.input))
   // A tool that targets a file (Read/Edit/Write…) renders its preview as a
   // tappable link that opens the file, independent of the line's expand tap.
   const filePath = call ? toolFilePath(call.input) : null
@@ -127,7 +140,7 @@ function ToolLine({
       {expanded ? (
         <View style={styles.toolDetail}>
           {callDiff ? <DiffView lines={callDiff} /> : null}
-          {!callDiff && call && preview ? <Text style={styles.mono}>{preview}</Text> : null}
+          {callDetail ? <Text style={styles.mono}>{callDetail}</Text> : null}
           {result ? (
             <ResultBody output={result.output} isError={result.isError} diff={resultDiff} />
           ) : null}
diff --git a/mobile/src/session/mobile-native-chat-tool-summary.test.ts b/mobile/src/session/mobile-native-chat-tool-summary.test.ts
index d08deec4b31..8e65ccf1958 100644
--- a/mobile/src/session/mobile-native-chat-tool-summary.test.ts
+++ b/mobile/src/session/mobile-native-chat-tool-summary.test.ts
@@ -1,5 +1,10 @@
 import { describe, expect, it, vi } from 'vitest'
-import { briefToolArg, summarizeToolInput, toolFilePath } from './mobile-native-chat-tool-summary'
+import {
+  briefToolArg,
+  describeToolInput,
+  summarizeToolInput,
+  toolFilePath
+} from './mobile-native-chat-tool-summary'
 
 describe('summarizeToolInput', () => {
   it('passes short strings through, collapsing whitespace', () => {
@@ -53,6 +58,13 @@ describe('toolFilePath', () => {
   })
 })
 
+describe('describeToolInput', () => {
+  it('is re-exported and labels rows with the path or primary argument', () => {
+    expect(describeToolInput({ file_path: 'src/a.ts', offset: 3 })).toBe('src/a.ts')
+    expect(describeToolInput('{"cmd":"git status"}')).toBe('git status')
+  })
+})
+
 describe('briefToolArg', () => {
   it('takes the basename of a forward-slash path', () => {
     expect(briefToolArg({ path: 'src/session/app.ts' })).toBe('app.ts')
diff --git a/mobile/src/session/mobile-native-chat-tool-summary.ts b/mobile/src/session/mobile-native-chat-tool-summary.ts
index bc3f7a2f89a..375b6312bcb 100644
--- a/mobile/src/session/mobile-native-chat-tool-summary.ts
+++ b/mobile/src/session/mobile-native-chat-tool-summary.ts
@@ -1,6 +1,9 @@
 export {
   briefToolArg,
   countToolCalls,
+  describeToolInput,
+  formatToolInput,
+  isStructuredToolInput,
   summarizeToolInput,
   summarizeToolRun,
   toolFilePath
diff --git a/src/shared/native-chat-tool-summary.test.ts b/src/shared/native-chat-tool-summary.test.ts
index ef6b385806d..cb710e6e71a 100644
--- a/src/shared/native-chat-tool-summary.test.ts
+++ b/src/shared/native-chat-tool-summary.test.ts
@@ -1,6 +1,77 @@
 import { describe, expect, it } from 'vitest'
 import type { NativeChatBlock } from './native-chat-types'
-import { briefToolArg, summarizeToolInput, summarizeToolRun } from './native-chat-tool-summary'
+import {
+  briefToolArg,
+  describeToolInput,
+  formatToolInput,
+  isStructuredToolInput,
+  summarizeToolInput,
+  summarizeToolRun,
+  toolFilePath
+} from './native-chat-tool-summary'
+
+describe('describeToolInput', () => {
+  it('labels a file-target call with its path, not raw JSON', () => {
+    expect(describeToolInput({ file_path: '/repo/src/app/Main.tsx', offset: 10 })).toBe(
+      '/repo/src/app/Main.tsx'
+    )
+    expect(describeToolInput({ path: 'src/index.ts' })).toBe('src/index.ts')
+    expect(describeToolInput({ file_path: 'C:\\Users\\me\\project\\app.tsx' })).toBe(
+      'C:\\Users\\me\\project\\app.tsx'
+    )
+  })
+
+  it('labels a command-shaped call with its primary argument', () => {
+    expect(describeToolInput({ command: 'pnpm test', description: 'Run tests' })).toBe('pnpm test')
+    expect(describeToolInput({ pattern: 'foo.*bar', glob: '*.ts' })).toBe('foo.*bar')
+    expect(describeToolInput({ url: 'https://example.com', description: 'Fetch it' })).toBe(
+      'https://example.com'
+    )
+    expect(describeToolInput({ description: 'Only prose' })).toBe('Only prose')
+  })
+
+  it('falls back to the bounded JSON preview for other shapes', () => {
+    expect(describeToolInput({ todos: [{ id: 1 }] })).toBe(
+      summarizeToolInput({ todos: [{ id: 1 }] })
+    )
+    expect(describeToolInput({ command: '   ' })).toBe(summarizeToolInput({ command: '   ' }))
+    expect(describeToolInput('raw string input')).toBe('raw string input')
+    expect(describeToolInput(null)).toBe('')
+  })
+
+  it('truncates an overlong path like any other preview', () => {
+    const path = `/very/${'long/'.repeat(30)}file.ts`
+    expect(describeToolInput({ file_path: path }).length).toBeLessThanOrEqual(80)
+    expect(describeToolInput({ file_path: path })).toContain('…')
+  })
+})
+
+describe('Codex JSON-string tool arguments', () => {
+  it('normalizes them for labels, details, file links and run summaries', () => {
+    expect(describeToolInput('{"cmd":"git status --short"}')).toBe('git status --short')
+    expect(formatToolInput('{"cmd":"git status --short"}')).toBe(
+      '{\n  "cmd": "git status --short"\n}'
+    )
+    expect(toolFilePath('{"file_path":"src/index.ts"}')).toBe('src/index.ts')
+    expect(briefToolArg('{"file_path":"src/app/index.ts"}')).toBe('index.ts')
+    expect(briefToolArg('{"cmd":"git status --short"}')).toBe('git status --short')
+    expect(isStructuredToolInput('{"cmd":"ls"}')).toBe(true)
+  })
+
+  it('joins an argv-array command into one label', () => {
+    expect(describeToolInput('{"command":["bash","-lc","make"]}')).toBe('bash -lc make')
+    expect(briefToolArg({ command: ['bash', '-lc', 'make'] })).toBe('bash -lc make')
+  })
+
+  it('leaves prose and malformed JSON as plain strings', () => {
+    expect(describeToolInput('{ not json')).toBe('{ not json')
+    expect(formatToolInput('just prose')).toBe('just prose')
+    expect(toolFilePath('{"file_path":')).toBeNull()
+    expect(isStructuredToolInput('just prose')).toBe(false)
+    // A JSON scalar is not an argument object — keep the literal text.
+    expect(formatToolInput('"quoted"')).toBe('"quoted"')
+  })
+})
 
 describe('summarizeToolInput bounded preview', () => {
   it('collapses depth beyond the bound instead of serializing the whole tree', () => {
diff --git a/src/shared/native-chat-tool-summary.ts b/src/shared/native-chat-tool-summary.ts
index efe606f55a9..251963f5c07 100644
--- a/src/shared/native-chat-tool-summary.ts
+++ b/src/shared/native-chat-tool-summary.ts
@@ -13,49 +13,112 @@ export function summarizeToolInput(input: unknown): string {
     : `${collapsed.slice(0, MAX_PREVIEW_LENGTH - 1)}…`
 }
 
-/** Full, pretty-printed tool-call input for the expanded detail view. Strings
- *  pass through as-is; objects/arrays print as indented JSON so a diff-less call
- *  (e.g. a question payload) reads cleanly instead of one long minified line. */
+/** Human label for a tool line: the target file path, else the primary string
+ *  argument (command/query/…), else the bounded JSON preview. Keeps raw
+ *  `{"file_path":…}` JSON out of the tappable row label. */
+export function describeToolInput(input: unknown): string {
+  const normalized = normalizeToolInput(input)
+  const path = toolFilePath(normalized)
+  if (path) {
+    return summarizeToolInput(path)
+  }
+  if (normalized && typeof normalized === 'object') {
+    const value = normalized as Record<string, unknown>
+    // Concrete target/action first; prose `description` only as a last resort.
+    const primary =
+      value.command ?? value.cmd ?? value.query ?? value.pattern ?? value.url ?? value.description
+    const primarySummary = summarizePrimaryToolArg(primary)
+    if (primarySummary) {
+      return primarySummary
+    }
+  }
+  return summarizeToolInput(normalized)
+}
+
+/** Full, pretty-printed tool-call input for the expanded detail view. Structured
+ *  JSON strings and objects/arrays print as indented JSON so a diff-less call
+ *  (e.g. a question payload) reads cleanly instead of one long minified line;
+ *  other strings pass through as-is. */
 export function formatToolInput(input: unknown): string {
-  if (input === null || input === undefined) {
+  const normalized = normalizeToolInput(input)
+  if (normalized === null || normalized === undefined) {
     return ''
   }
-  if (typeof input === 'string') {
-    return input
+  if (typeof normalized === 'string') {
+    return normalized
   }
-  if (typeof input === 'number' || typeof input === 'boolean') {
-    return String(input)
+  if (typeof normalized === 'number' || typeof normalized === 'boolean') {
+    return String(normalized)
   }
   try {
-    return JSON.stringify(input, null, 2) ?? ''
+    return JSON.stringify(normalized, null, 2) ?? ''
   } catch {
     return ''
   }
 }
 
+/** Whether the expanded detail would show structured JSON rather than repeating
+ *  the row label — i.e. whether expanding the row is worth offering. */
+export function isStructuredToolInput(input: unknown): boolean {
+  const normalized = normalizeToolInput(input)
+  return normalized !== null && typeof normalized === 'object'
+}
+
 export function toolFilePath(input: unknown): string | null {
-  if (!input || typeof input !== 'object') {
+  const normalized = normalizeToolInput(input)
+  if (!normalized || typeof normalized !== 'object') {
     return null
   }
-  const value = input as Record<string, unknown>
+  const value = normalized as Record<string, unknown>
   const path = value.file_path ?? value.filePath ?? value.path ?? value.notebook_path
   return typeof path === 'string' && path.length > 0 ? path : null
 }
 
 export function briefToolArg(input: unknown): string {
-  if (input && typeof input === 'object') {
-    const value = input as Record<string, unknown>
+  const normalized = normalizeToolInput(input)
+  if (normalized && typeof normalized === 'object') {
+    const value = normalized as Record<string, unknown>
     const path = value.file_path ?? value.filePath ?? value.path ?? value.notebook_path
     if (typeof path === 'string' && path.length > 0) {
       const parts = path.split(/[\\/]/).filter(Boolean)
       return parts.at(-1) ?? path
     }
     const command = value.command ?? value.cmd ?? value.query ?? value.pattern
-    if (typeof command === 'string') {
-      return summarizeToolInput(command).slice(0, 28)
+    const commandSummary = summarizePrimaryToolArg(command)
+    if (commandSummary) {
+      return commandSummary.slice(0, 28)
     }
   }
-  return summarizeToolInput(input).slice(0, 28)
+  return summarizeToolInput(normalized).slice(0, 28)
+}
+
+/** Codex delivers tool arguments as a JSON string. Parse those into the object
+ *  shape every helper below already understands; leave prose strings alone. */
+function normalizeToolInput(input: unknown): unknown {
+  if (typeof input !== 'string') {
+    return input
+  }
+  const first = input.trimStart()[0]
+  if (first !== '{' && first !== '[') {
+    return input
+  }
+  try {
+    const parsed: unknown = JSON.parse(input)
+    return parsed !== null && typeof parsed === 'object' ? parsed : input
+  } catch {
+    return input
+  }
+}
+
+/** A label-worthy primary argument: a non-blank string, or an argv array. */
+function summarizePrimaryToolArg(input: unknown): string | null {
+  if (typeof input === 'string' && input.trim()) {
+    return summarizeToolInput(input)
+  }
+  if (Array.isArray(input) && input.length > 0 && input.every((part) => typeof part === 'string')) {
+    return summarizeToolInput(input.join(' '))
+  }
+  return null
 }
 
 export function summarizeToolRun(blocks: readonly NativeChatBlock[]): string {