Built-in tools

Call contracts for the two built-in tools: emit_output (terminates autonomous runs) and reason (typed think-step inference), with every error code.

Context — The runtime ships two synthetic tools under the built-in namespace. Authors normally meet them through routine syntax (think: steps; autonomous terminal steps); this page is the exact call contract — what the model is asked to supply and every result the handler can return.

Both tools take nested JSON as a JSON-encoded string parameter (output_json) — tool parameters are primitive-typed, so objects are marshalled through strings. Both return {"ok": true, ...} on success and {"ok": false, "error": <code>, ...} on failure; a failed call is visible to the model, which can retry with corrected output within the turn's iteration budget.

built-in:emit_output

Terminates an autonomous run with its typed result. Every terminal node of an autonomous routine (a node with no outbound transitions) must be a TOOL node calling it.

Parameter	Type	Meaning
output_json	string (JSON-encoded object)	The run's final output. Must parse as JSON and validate against the routine's output_schema (tightened with additionalProperties: false).

On success the run transitions to succeeded and the callback watcher fires. Schema violations transition the run to failed with error code output_validation_failed (the callback's error.details carries the violating path).

Result error	Meaning
output_validation_failed	output_json didn't parse, or violated output_schema — the run fails.
not_an_autonomous_run	Called in a session that isn't an autonomous run.
routine_not_registered	Session metadata names a routine the runtime doesn't know.
session_not_found	The session disappeared mid-run.
not_configured	Autonomous runtime not wired (server misconfiguration).

Usage in a routine:

- id: finish
  tools: built-in:emit_output
  tool_instruction: >
    Call emit_output with output_json set to a JSON object
    containing exactly the decision and explanation fields
    produced by the assess node.

built-in:reason

Backs the think: node kind — typed structured inference that does not end the turn. The loader compiles each think: + output_schema: node into a TOOL node calling this tool with the node's id baked into the instruction.

Parameter	Type	Meaning
step_id	string	The think node's id (the parameter keeps its historical wire name; the value is compiled into the node's instruction — not chosen at runtime).
output_json	string (JSON-encoded object)	The inference result. Must validate against the node's output_schema (tightened with additionalProperties: false).

On success the validated object is merged into session.metadata.step_outputs[<node-id>] and returned in the tool result, so downstream steps see the typed fields in history.

Result error	Meaning
output_validation_failed	output_json didn't parse or violated the node's schema — the model can correct and retry.
missing_step_id	Empty step_id argument.
step_not_registered	No output_schema registered for this routine + node id.
routine_not_resolved	The session has no routine_id metadata. Autonomous runs set it automatically, so this indicates a misconfiguration.
session_not_found	The session disappeared.
persist_failed	Writing step_outputs to the session failed.
not_configured	Reason-step registry not wired (server misconfiguration).

Authoring guidance for think nodes (autonomous routines only): Autonomous routines.