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A small, precise vocabulary runs through the whole system. Learn these and the rest of the docs read cleanly.

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Surface

The surface of an API is everything that describes how to call it: methods, paths, parameters, request/response schemas, auth schemes. It is not the data the API returns. Gecko ingests the surface and nothing more — this is the basis of the control-plane promise.

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Operation

A single callable endpoint, normalized from the spec into a typed record: method, path, operation_id, summary/description, tags, parameters, request body, responses, and security. Local $refs are resolved (with cycle and depth guards) so each operation is self-contained.

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Parameter

A normalized input to an operation, carrying its name, location (path / query / header / cookie), whether it’s required, and its schema. The location is what lets the caller place each agent-supplied value in the right spot.

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Catalog

The “find the right endpoint” layer. It does lexical search over each operation’s surface text (summary, description, path, tags, id), with summary matches weighted highest. At the scale of tens of endpoints this is more accurate and far simpler than vector search — vectorization is a deliberately deferred multi-API concern.

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Question-shaped tool

The comprehension payload: an operation rendered as an agent-reasonable tool definition — a name, a question-shaped description, and a JSON-Schema input. Two decisions separate it from a raw OpenAPI dump:
  • Auth is hidden. Authorization-style headers are removed from the agent-facing input. The agent only sees decision-relevant inputs.
  • Invocation metadata travels with the tool. The method, path, and per-parameter locations ride along so the caller can build a real request without re-parsing the spec.
Each tool also carries requires_auth and the auth_schemes it references, so a session with no credentials can hide operations it could never satisfy.

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Session

The access/auth seam. Any object with auth_headers() -> dict[str, str] is a valid session. A paywalled API returns its tokens; a public API returns an empty dict. The agent never sees these headers — Gecko injects them at call time. See Access & auth.

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Caller

Turns a question-shaped tool plus the agent’s arguments into a correct HTTP request: it places each value in the right location (path / query / header), injects the hidden auth headers, and catches the failure the agent can’t see — like a missing required path parameter — instead of firing a malformed call.

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Modes: recorded vs live

Gecko runs one code path in two modes: They differ only at the transport edge. See Recorded mode.

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First-call-correct

The bar Gecko holds itself to: given a natural-language goal, retrieve the right operation and build a well-formed request for it on the first try — no trial calls, no malformed requests the agent can’t diagnose. A built-in evaluation scores retrieval (top-1 / top-5) and request well-formedness against a task set.