Event Types Reference

Complete catalog of all NDJSON events emitted by claude -p --output-format stream-json --verbose.

Top-Level Event Types

Every stdout line is a JSON object with a type field. These are the possible values:

Type	When	Contains
`system`	First event of a run	Session metadata, tools, model
`stream_event`	During streaming	Content deltas, tool call fragments
`assistant`	After streaming completes	Fully assembled message
`result`	Final event	Cost, usage, session ID, errors
`rate_limit_event`	When rate limited	Reset time, limit type
`permission_request`	When tool needs approval	Tool name, input, options

system (init)

The first event. Subtype is always init.

{
  "type": "system",
  "subtype": "init",
  "cwd": "/Users/me/project",
  "session_id": "abc-def-123",
  "tools": ["Read", "Write", "Edit", "Bash", "Glob", "Grep", "LS", "Agent", "Task", "WebSearch", "WebFetch"],
  "mcp_servers": [{"name": "my-server", "status": "connected"}],
  "model": "claude-sonnet-4-20250514",
  "permissionMode": "default",
  "agents": [],
  "skills": ["skill-name"],
  "plugins": [],
  "claude_code_version": "2.1.63",
  "fast_mode_state": "disabled",
  "uuid": "event-uuid"
}

Key fields:

session_id - store this for --resume
tools - available tool names (varies by installation and MCP servers)
model - the active model
mcp_servers - connected MCP servers and their status
claude_code_version - for compatibility checks

stream_event

Wraps Anthropic API streaming events. Has a nested event object.

{
  "type": "stream_event",
  "event": { ... },
  "session_id": "abc-def-123",
  "parent_tool_use_id": null,
  "uuid": "event-uuid"
}

The parent_tool_use_id is non-null when the event comes from a subagent (tool-within-tool execution).

Sub-event: message_start

Signals beginning of a new assistant message.

{
  "type": "stream_event",
  "event": {
    "type": "message_start",
    "message": {
      "model": "claude-sonnet-4-20250514",
      "id": "msg_abc123",
      "role": "assistant",
      "content": [],
      "stop_reason": null,
      "usage": {"input_tokens": 100, "output_tokens": 0}
    }
  }
}

Sub-event: content_block_start (text)

A text content block begins.

{
  "type": "stream_event",
  "event": {
    "type": "content_block_start",
    "index": 0,
    "content_block": {"type": "text", "text": ""}
  }
}

Sub-event: content_block_start (tool_use)

A tool call begins. Extract the tool name and id.

{
  "type": "stream_event",
  "event": {
    "type": "content_block_start",
    "index": 1,
    "content_block": {
      "type": "tool_use",
      "id": "toolu_abc123",
      "name": "Read",
      "input": {}
    }
  }
}

Sub-event: content_block_delta (text)

Streaming text fragment. Append delta.text to your display.

{
  "type": "stream_event",
  "event": {
    "type": "content_block_delta",
    "index": 0,
    "delta": {"type": "text_delta", "text": "Here is the "}
  }
}

Sub-event: content_block_delta (tool input)

Streaming tool input JSON fragment. Accumulate partial_json to reconstruct the full tool input.

{
  "type": "stream_event",
  "event": {
    "type": "content_block_delta",
    "index": 1,
    "delta": {"type": "input_json_delta", "partial_json": "{\"file_path\":\""}
  }
}

Sub-event: content_block_stop

A content block (text or tool_use) is complete.

{
  "type": "stream_event",
  "event": {
    "type": "content_block_stop",
    "index": 0
  }
}

Sub-event: message_delta

Message-level update with stop reason and usage.

{
  "type": "stream_event",
  "event": {
    "type": "message_delta",
    "delta": {"stop_reason": "end_turn"},
    "usage": {"input_tokens": 100, "output_tokens": 250}
  }
}

Stop reasons: "end_turn" (normal), "tool_use" (needs to call a tool), "max_tokens" (hit limit).

Sub-event: message_stop

Message streaming is complete.

{
  "type": "stream_event",
  "event": {"type": "message_stop"}
}

assistant

Assembled message after streaming completes. Contains all content blocks with their full content.

{
  "type": "assistant",
  "message": {
    "model": "claude-sonnet-4-20250514",
    "id": "msg_abc123",
    "role": "assistant",
    "content": [
      {"type": "text", "text": "I'll read that file for you."},
      {"type": "tool_use", "id": "toolu_abc123", "name": "Read", "input": {"file_path": "/tmp/test.txt"}}
    ],
    "stop_reason": "tool_use",
    "usage": {"input_tokens": 100, "output_tokens": 50}
  },
  "parent_tool_use_id": null,
  "session_id": "abc-def-123",
  "uuid": "event-uuid"
}

Use this event to get complete tool inputs (instead of reconstructing from input_json_delta fragments).

result

Final event of a run. Always present, even on errors.

Success

{
  "type": "result",
  "subtype": "success",
  "is_error": false,
  "duration_ms": 15234,
  "num_turns": 3,
  "result": "The file contains a list of...",
  "total_cost_usd": 0.0034,
  "session_id": "abc-def-123",
  "usage": {
    "input_tokens": 5000,
    "output_tokens": 1200,
    "cache_read_input_tokens": 3000,
    "cache_creation_input_tokens": 500
  },
  "permission_denials": [],
  "uuid": "event-uuid"
}

Error

{
  "type": "result",
  "subtype": "error",
  "is_error": true,
  "result": "Error: rate limit exceeded",
  "session_id": "abc-def-123",
  "duration_ms": 1200,
  "num_turns": 0,
  "total_cost_usd": 0,
  "usage": {},
  "permission_denials": [],
  "uuid": "event-uuid"
}