Tools

A tool is a function the LLM can call during a turn: look up an order, book a slot, transfer the call. brisvox's tool contract is built around the two things that go wrong in voice: a tool that runs when it should not, and a caller who is kept waiting in silence.

Kinds

• read_only tools only look things up. They may run on a speculative LLM start, they are cancelled when the caller interrupts, and running one twice is harmless.
• side_effect tools change the world (book, cancel, transfer, charge). They never run speculatively (they are held until the turn is committed and discarded if the speculation is cancelled), never run twice (the idempotency key is derived from the session, the turn epoch and the call id; a replay of that call returns the recorded result, and an identical call in a later response of the same turn is refused as already_done; a later turn or another call is not covered, so use your own idempotency key for rules such as "one refund per order, ever"), and are not cancelled by an interruption: they complete, are recorded, and the outcome is reported to the LLM on the next turn.

Lifecycle of a call

1. The LLM streams a tool call; the argument deltas are buffered until complete. Partial JSON never executes.
2. The arguments are validated against the tool's JSON Schema. A failure goes back to the LLM as a structured error, with bounded retries and then a spoken fallback.
3. Independent calls run in parallel; results are appended to the context in the order the LLM issued them.
4. If a tool has not answered after a delay (1.2 s by default, or the tool's own filler_after), the agent says a filler phrase so the line is not silent.

Where tools come from

• Built-in telephony tools: transfer_call, send_dtmf, end_call, over the carrier's REST call control (Telephony).
• In-process tools: Rust tools registered through brisvox_server::tools::AppTools; an agent file lists, by name, the ones the LLM may see. Your own binary is one line, brisvox_server::app::run_with_tools(Arc::new(MyTools)); examples/rust-tools is a complete project.
• Remote tools in your own process, through the Python or TypeScript SDK and the agent protocol.

Read more: the Tools reference (the contract, the tool engine, filler and interruption semantics, per-request LLM metrics) and Configuration (the tools key of an agent file).