Fact It API
Real-time fact-checking for AI-generated text. POST a response and Fact It extracts its claims, retrieves live evidence, and returns a per-claim verdict — each with a confidence score and citations — plus an importance-weighted trust score for the whole response.
How it works
Under the hood a cheap extractor model pulls the checkable claims out of the text, then a smarter verifier weighs each claim against live sources (Wikipedia, web search, and domain-specific corpora) to produce a verdict. You send text and read back structured JSON — the models and providers are ours to run.
Base URL
The hosted API is served at https://fact-it-web-412159981305.us-central1.run.app— Fact It's current deployment origin, and the placeholder used in every example on these pages. If you self-host the @fact-it/api service or run behind your own domain, swap in that origin instead. Every request and response body is validated against the Zod schemas in @fact-it/shared; the OpenAPI 3.1 spec is generated from those same schemas, so it can never drift from what the server accepts.
Endpoints
| Method | Path | What it does |
|---|---|---|
| POST | /api/check | Fact-check a response |
| POST | /api/check/stream | Fact-check a response (streaming) |
| POST | /api/feedback | Rate a check |
| GET | /api/account/usage | Get credit balance |
Authentication
/api/check and /api/check/stream require authentication — an API token (Authorization: Bearer fk_…), or a session cookie from the signed-in dashboard. Unauthenticated calls get a 401. Mint a token and see the details in Authentication.
Self-host
Prefer to run it yourself? The @fact-it/api service (a small Hono server) exposes a contract-identical /check, /check/stream, and /health, gated by a single shared FACT_IT_API_TOKEN. Same request and response shapes as the hosted API.
Next steps
- Quickstart — make your first check in a couple of minutes.
- API reference — every endpoint, field, and data type.
- OpenAPI spec — drop into Postman or a codegen tool.