prebuilt.react

react_agent

react_agent(...) builds a ReAct loop as a Step.

Key parameters:

• planner: an LLM step created with llm_step(...)
• tools: mapping from names to tool steps created with tool_step(...)
• max_steps / policy.max_iterations: maximum iterations
• Key overrides for where data is stored in state (llm_response_key, tool_result_key, etc.)

State keys and defaults

Default keys:

• llm_response: LLMResponse returned by the planner
• tool_name: name of the tool to run
• tool_args: dict of tool arguments
• tool_result: tool output
• tool_call_id: tool call identifier (if present)
• final: final assistant text (stop condition)

Tool validation and dispatch

Validation rules:

• Every entry in tools must be a Step
• Each tool step must have annotations["kind"] == "tool"
• Tool step names must be unique

Dispatch rules:

• ReAct executes only the first tool call in LLMResponse.tool_calls per iteration
• If the tool name cannot be resolved, a KeyError is raised
• If the tool does not set the configured result key, an error is raised

Next steps

ReAct pattern

The conceptual flow and state contract.

Tools concept

How to build tool steps and tool specs.