Claude stream-json event cheatsheet

claude -p --output-format stream-json --verbose writes one JSON object per line (JSONL) with a required type field. (--output-format only works with -p.)

This cheatsheet is derived from humanlayer/claudecode-go/types.go and client_test.go.

Top-level event lines

system (init)

Fields: - type: "system" - subtype: "init" - session_id - tools: array of tool names - mcp_servers: array of {name, status} - cwd, model, permissionMode, apiKeySource (optional)

Example:

{"type":"system","subtype":"init","session_id":"session_01","cwd":"/repo","model":"sonnet","permissionMode":"auto","apiKeySource":"env","tools":["Bash","Read","Write","WebSearch"],"mcp_servers":[{"name":"approvals","status":"connected"}]}

assistant / user

Fields: - type: "assistant" or "user" - session_id - message (see below)

Example (assistant text):

{"type":"assistant","session_id":"session_01","message":{"id":"msg_1","type":"message","role":"assistant","content":[{"type":"text","text":"Planning next steps."}],"usage":{"input_tokens":120,"output_tokens":45}}}

Example (assistant tool use):

{"type":"assistant","session_id":"session_01","message":{"id":"msg_2","type":"message","role":"assistant","content":[{"type":"tool_use","id":"toolu_1","name":"Bash","input":{"command":"ls -la"}}]}}

Example (user tool result, string content):

{"type":"user","session_id":"session_01","message":{"id":"msg_3","type":"message","role":"user","content":[{"type":"tool_result","tool_use_id":"toolu_1","content":"total 2\nREADME.md\nsrc\n"}]}}

Example (user tool result, array content):

{"type":"user","session_id":"session_01","message":{"id":"msg_4","type":"message","role":"user","content":[{"type":"tool_result","tool_use_id":"toolu_2","content":[{"type":"text","text":"Task completed"}]}]}}

Optional parent field (for nested tool usage):

{"type":"assistant","parent_tool_use_id":"toolu_parent","session_id":"session_01", ...}

result

Fields (success path): - type: "result" - subtype: "success" (or "completion") - session_id - total_cost_usd, is_error, duration_ms, duration_api_ms, num_turns - result: final answer string - usage: usage object - modelUsage: optional per-model usage

Example (success):

{"type":"result","subtype":"success","session_id":"session_01","total_cost_usd":0.0123,"is_error":false,"duration_ms":12345,"duration_api_ms":12000,"num_turns":2,"result":"Done.","usage":{"input_tokens":150,"output_tokens":70,"service_tier":"standard","server_tool_use":{"web_search_requests":0}}}

Example (error + permission denials):

{"type":"result","subtype":"error","session_id":"session_02","total_cost_usd":0.001,"is_error":true,"duration_ms":2000,"duration_api_ms":1800,"num_turns":1,"result":"","error":"Permission denied","permission_denials":[{"tool_name":"Bash","tool_use_id":"toolu_9","tool_input":{"command":"git fetch origin main"}}]}

Message object (message field)

Fields: - id, type, role - model (optional) - content: array of content blocks - usage (assistant messages)

Content block shapes (in message.content[])

Text

{"type":"text","text":"Hello"}

Tool use

{"type":"tool_use","id":"toolu_1","name":"Bash","input":{"command":"ls -la"}}

Tool result

String content:

{"type":"tool_result","tool_use_id":"toolu_1","content":"ok"}

Array content (Task tool format):

{"type":"tool_result","tool_use_id":"toolu_2","content":[{"type":"text","text":"Task done"}]}