Fax for Agents
Send a fax
Menu
Documentation API reference

API reference

Updated

The REST API is at https://api.faxforagents.com/v1. The reference is built from the server's own OpenAPI 3.1 document, snapshot of 2026-11-13, version 1.20.1. 169 operations in 20 groups and 173 schemas.

How do I read the reference?

  • The full reference as plain HTML: every operation, parameter, body, response and schema, one page per group. Loads with no JavaScript and reads well on a phone.
  • openapi.json and openapi.yaml: the document itself, for a generator or a client.
  • arazzo.yaml: the send flow as Arazzo 1.0 workflows over the same document. Upload or render, quote, wait for a person's approval, send and poll the job.
  • The interactive explorer below, which loads a third-party viewer on demand.
  • github.com/faxforagents/openapi: the same document in a public repository, with a changelog per version.

How do I authenticate?

Send Authorization: Bearer ffa_test_... or X-API-Key: ffa_test_... on every call that needs a key. Test keys reach the sandbox, live keys reach the carrier. Every mutating call accepts an Idempotency-Key.

The OpenAPI document says what each operation takes. Its security list names the credentials the operation accepts. There are four: an API key, a signed-in session, the status token of a one-time order and a signed URL. An empty list means the call needs none, as for signing in and the public one-time send. x-required-scope names the scope the call requires. Signed upload and download URLs take no key. An OAuth access token from the MCP sign-in works on the MCP server only. The REST API answers it with 401 invalid_token. Each operation also lists the error statuses it can answer, and all of them carry the same error envelope.

Signed-in sessions use X-FFA-Environment: test or X-FFA-Environment: live to select the environment for each request. Without this header, sessions default to test. API credentials keep their own environment regardless of this header.

Test number orders create simulated reservations for your organization. They do not purchase carrier numbers or block live orders.

Groups

Interactive explorer

The explorer is a 3 MB third-party viewer, loaded only when you ask for it, pinned to one version and checked against its published hash. It reads /openapi.json from this site and lets you try calls with your own key. Your API key goes to api.faxforagents.com and nowhere else.