Codex exec --json event cheatsheet

codex exec --json writes one JSON object per line (JSONL) to stdout. Each line is a top-level thread event with a type field.

Below: required + commonly emitted fields for every line type plus a full-line example for each shape that can be emitted. Fields noted as optional may be omitted (or null) depending on Codex version and lifecycle. Unknown fields may appear; ignore what you don't use.

Top-level event lines (non-item)

thread.started

Fields: - type - thread_id

Example:

{"type":"thread.started","thread_id":"0199a213-81c0-7800-8aa1-bbab2a035a53"}

turn.started

Fields: - type

Example:

{"type":"turn.started"}

turn.completed

Fields: - type - usage.input_tokens - usage.cached_input_tokens - usage.output_tokens

Example:

{"type":"turn.completed","usage":{"input_tokens":24763,"cached_input_tokens":24448,"output_tokens":122}}

turn.failed

Fields: - type - error.message

Example:

{"type":"turn.failed","error":{"message":"model response stream ended unexpectedly"}}

error

Fields: - type - message

Example:

{"type":"error","message":"stream error: broken pipe"}

Note: Codex may emit transient reconnect notices as type="error" with messages like "Reconnecting... 1/5" while it retries a dropped stream. Treat those as non-fatal progress updates (the turn continues).

Item event lines (item.*)

Every item line includes: - type (item.started, item.updated, or item.completed) - item.id - item.type - fields for the specific item.type below

item.id is stable for the item; updates/completion reuse the same id.

agent_message (only item.completed)

Fields: - item.text

Example:

{"type":"item.completed","item":{"id":"item_3","type":"agent_message","text":"Done. I updated the docs and added examples."}}

reasoning (only item.completed, if enabled)

Fields: - item.text

Example:

{"type":"item.completed","item":{"id":"item_0","type":"reasoning","text":"**Scanning docs for exec JSON schema**"}}

command_execution (item.started and item.completed)

Fields: - item.command - item.aggregated_output - item.exit_code (null or omitted until completion) - item.status (in_progress, completed, failed)

Example (started):

{"type":"item.started","item":{"id":"item_1","type":"command_execution","command":"bash -lc ls","aggregated_output":"","exit_code":null,"status":"in_progress"}}

Example (completed, success):

{"type":"item.completed","item":{"id":"item_1","type":"command_execution","command":"bash -lc ls","aggregated_output":"docs\nsrc\n","exit_code":0,"status":"completed"}}

Example (completed, failure):

{"type":"item.completed","item":{"id":"item_2","type":"command_execution","command":"bash -lc false","aggregated_output":"","exit_code":1,"status":"failed"}}

Note: aggregated_output is truncated to 64 KiB; truncated output ends with \n...(truncated).

file_change (only item.completed)

Fields: - item.changes[].path - item.changes[].kind (add, delete, update) - item.status (completed, failed)

Example:

{"type":"item.completed","item":{"id":"item_4","type":"file_change","changes":[{"path":"docs/exec-json-cheatsheet.md","kind":"add"},{"path":"docs/exec.md","kind":"update"}],"status":"completed"}}

mcp_tool_call (item.started and item.completed)

Fields: - item.server - item.tool - item.arguments (JSON value; defaults to null if absent) - item.result (object or null; may be omitted) - item.result.content (array of MCP content blocks) - item.result.structured_content (JSON value or null) - item.error (object or null; may be omitted) - item.error.message (if error is present) - item.status (in_progress, completed, failed)

Example (started):

{"type":"item.started","item":{"id":"item_5","type":"mcp_tool_call","server":"docs","tool":"search","arguments":{"q":"exec --json"},"result":null,"error":null,"status":"in_progress"}}

Example (completed, success):

{"type":"item.completed","item":{"id":"item_5","type":"mcp_tool_call","server":"docs","tool":"search","arguments":{"q":"exec --json"},"result":{"content":[{"type":"text","text":"Found 3 matches.","annotations":{"audience":["assistant"],"lastModified":"2025-01-01T00:00:00Z","priority":0.5}}],"structured_content":{"matches":3}},"error":null,"status":"completed"}}

Example (completed, failure):

{"type":"item.completed","item":{"id":"item_6","type":"mcp_tool_call","server":"docs","tool":"search","arguments":{"q":"exec --json"},"result":null,"error":{"message":"tool timeout"},"status":"failed"}}

web_search (only item.completed)

Fields: - item.query

Example:

{"type":"item.completed","item":{"id":"item_7","type":"web_search","query":"codex exec --json schema"}}

todo_list (item.started, item.updated, and item.completed)

Fields: - item.items[].text - item.items[].completed

Example (started):

{"type":"item.started","item":{"id":"item_8","type":"todo_list","items":[{"text":"Scan docs","completed":false},{"text":"Write cheatsheet","completed":false}]}}

Example (updated):

{"type":"item.updated","item":{"id":"item_8","type":"todo_list","items":[{"text":"Scan docs","completed":true},{"text":"Write cheatsheet","completed":false}]}}

Example (completed):

{"type":"item.completed","item":{"id":"item_8","type":"todo_list","items":[{"text":"Scan docs","completed":true},{"text":"Write cheatsheet","completed":true}]}}

error (non-fatal warning as an item; only item.completed)

Fields: - item.message

Example:

{"type":"item.completed","item":{"id":"item_9","type":"error","message":"command output truncated"}}

MCP content block shapes (mcp_tool_call.result.content)

result.content is an array of content blocks. Each block is one of the types below; all optional fields may appear depending on the server.

Text content

Fields: - type - text - annotations.audience (optional) - annotations.lastModified (optional) - annotations.priority (optional)

Example block:

{"type":"text","text":"Hello","annotations":{"audience":["assistant"],"lastModified":"2025-01-01T00:00:00Z","priority":0.5}}

Image content

Fields: - type - data (base64) - mimeType - annotations.* (same as above, optional)

Example block:

{"type":"image","data":"<base64>","mimeType":"image/png","annotations":{"audience":["assistant"]}}

Audio content

Fields: - type - data (base64) - mimeType - annotations.* (optional)

Example block:

{"type":"audio","data":"<base64>","mimeType":"audio/wav","annotations":{"audience":["assistant"]}}

Resource link

Fields: - type - name - uri - description (optional) - mimeType (optional) - size (optional) - title (optional) - annotations.* (optional)

Example block:

{"type":"resource_link","name":"docs/exec.md","uri":"file:///repo/docs/exec.md","description":"Exec docs","mimeType":"text/markdown","size":1234,"title":"exec.md","annotations":{"audience":["assistant"]}}

Embedded resource

Fields: - type - resource (either text or blob contents) - annotations.* (optional)

Example block (embedded text):

{"type":"resource","resource":{"uri":"file:///repo/README.md","text":"Hello","mimeType":"text/markdown"},"annotations":{"audience":["assistant"]}}

Example block (embedded blob):

{"type":"resource","resource":{"uri":"file:///repo/image.png","blob":"<base64>","mimeType":"image/png"},"annotations":{"audience":["assistant"]}}

Consumer considerations (rendering + success/failure)

Use this section to decide what to surface to end users vs. what to treat as machine-only metadata.

What to render for users

• Final answer: render item.completed where item.type = "agent_message" as the main response.
• Progress updates (optional):
• item.completed with item.type = "reasoning" can be shown as brief activity breadcrumbs (only if you want to expose reasoning summaries).
• item.started / item.completed with item.type = "command_execution" can be shown as “running command …” status lines without printing full output.
• item.completed with item.type = "file_change" can be rendered as a list of changed paths and kinds (add/update/delete).
• item.* with item.type = "todo_list" can be shown as a progress checklist.
• Errors: render type = "error" and item.type = "error" as user-visible warnings or failures.

Fields you can safely skip for UX

• command_execution.aggregated_output is often noisy; many consumers omit or truncate it, and rely on command_execution.status + exit_code instead.
• mcp_tool_call.result.content can be large and tool-specific; consider showing only high-level status unless you know the tool’s schema.
• usage fields (turn.completed.usage.*) are typically telemetry-only.

Success and failure signals

• Turn success: type = "turn.completed" indicates overall success.
• Turn failure: type = "turn.failed" with error.message indicates failure.
• Item success/failure: use item.status on the item payload:
• command_execution.status: completed = success, failed = failure.
• file_change.status: completed = patch applied, failed = patch failed.
• mcp_tool_call.status: completed = tool succeeded, failed = tool failed.
• Fatal stream errors: type = "error" means the JSONL stream itself hit an unrecoverable error (except transient "Reconnecting... X/Y" notices, which are non-fatal).

Suggested minimal rendering

If you want a compact UI, the following is usually enough: - Thread/turn lifecycle: thread.started, turn.started, turn.completed or turn.failed - Final answer: item.completed with item.type = "agent_message" - Optional progress: item.started / item.completed for command_execution and file_change

Optional/conditional emission notes

• turn.failed only appears on failure; otherwise turn.completed is emitted.
• reasoning items only appear when reasoning summaries are enabled.
• todo_list items only appear when the plan tool is active; they are the primary source of item.updated.
• file_change and web_search items are emitted only as item.completed in the current codex exec --json stream.