Calls without X-API-Key need no key. Calls with it need a paid plan — get a key.
Get an API key
Free tier, no form to fill in. Signing in shares your email address with us — we
store it to create your key and to recognise you if you sign in with another
provider. See our Privacy Policy and
Terms.
openapi: 3.2.0
info:
title: FactReason Agent MCP API
version: 2.1.0
description: Public access, discovery, correction, and paid reference-data routes. Catalogue results remain protected by Bearer-key or x402 authorization.
servers:
- url: https://factreason.com
security:
- bearerAuth: []
tags:
- name: MCP
paths:
/mcp:
post:
summary: Use the Streamable HTTP MCP endpoint
description: 'Initialize the server and call tools/list for authoritative tool schemas. GET and DELETE answer 405 by design: this server offers no SSE stream.'
responses:
'200':
description: 'JSON-RPC response. A paid tool the caller cannot pay for returns a tool result with isError: true carrying the payment requirements (status 402) and a nextStep, never an HTTP 402.'
'405':
description: Method not allowed. Required by the Streamable HTTP spec when no SSE stream is offered.
tags:
- MCP
operationId: postMcp
x-operation-id-source: derived
components:
securitySchemes:
bearerAuth:
type: http
scheme: bearer
description: FactReason API key
externalDocs:
description: FactReason documentation
url: https://factreason.com/docs