Gemini --output-format stream-json event cheatsheet

Deprecated

The gemini engine is deprecated and no longer supported (as of v0.36.0): it still loads, but gets no fixes, is excluded from testing, and may be removed in a future release (#722). Google ended Gemini CLI support for individual accounts (free, Google AI Pro and Ultra) on 18 June 2026 (IneligibleTierError); under Untether the subprocess hangs until the watchdog cancels the run. Enterprise / Google Cloud licences are unverified. Antigravity CLI ships as a separate engine in v0.36.1 (#558), not a rename.

gemini --output-format stream-json --prompt=<prompt> writes one JSON object per line (JSONL) with a required type field.

Event types#

init#

Session initialisation with session ID and model.

{"type":"init","session_id":"abc123def","model":"gemini-2.0-flash-exp","timestamp":"2026-01-15T10:00:00Z"}

message#

Text content from user or assistant. Delta messages have delta: true.

{"type":"message","role":"assistant","content":"The command output `hello`.","timestamp":"2026-01-15T10:00:05Z"}

tool_use#

Tool invocation with name, ID, and parameters.

{"type":"tool_use","tool_name":"Bash","tool_id":"tool_1","parameters":{"command":"echo hello"},"timestamp":"2026-01-15T10:00:01Z"}

File operation example:

{"type":"tool_use","tool_name":"write_file","tool_id":"tool_2","parameters":{"file_path":"notes.md","content":"hello"},"timestamp":"2026-01-15T10:00:03Z"}

tool_result#

Tool completion with status and output.

{"type":"tool_result","tool_id":"tool_1","status":"success","output":"hello","timestamp":"2026-01-15T10:00:02Z"}

result#

Final result with status and token usage stats.

{"type":"result","status":"success","stats":{"input_tokens":100,"output_tokens":50},"timestamp":"2026-01-15T10:00:06Z"}

Stats may also include total_cost_usd:

{"type":"result","status":"success","stats":{"input_tokens":100,"output_tokens":50,"total_cost_usd":0.0025},"timestamp":"2026-01-15T10:00:06Z"}

error#

Error with message. Terminates the session.

{"type":"error","message":"API key invalid or expired","timestamp":"2026-01-15T10:00:01Z"}

Notes#

• init is always the first event and contains session_id for resume.
• message events with role = "assistant" accumulate to form the final answer text.
• tool_use and tool_result events are paired by tool_id.
• result is the terminal event for successful runs; error for failures.
• Tool names are snake_case (e.g., read_file, edit_file, write_file).