# Polygraph

> Claim-level fact-checking that shows how a post misleads. A Pluribus Labs product.

## What it is

Polygraph checks a social post claim by claim. Each claim gets one of exactly four verdicts: true, false, mixed, unverifiable. Every claim a post makes is verified; none are skipped. Each verdict comes with a calibrated confidence, a short summary, and the sources it rests on, each source rated by tier. A verdict describes a claim, never a person. Only checks an editor has published appear on this site; nothing is public by default.

## How to read a check

A check page (/checks/<slug>) opens with the verdict summary, then the claims with their verdicts, the sources, and how the post misleads: the route it takes, its framing, and the basis of each verdict. A claim page (/claims/<slug>) is the citable unit: the claim verbatim, who said it and when, the verdict and confidence, a 40-60 word summary, the sources with tiers, the posts carrying the claim, the re-verification history, and the methodology version. Its first paragraph is the answer.

## Published checks

- [Fact checks](https://beta.polygraphs.xyz/fact-checks): published checks plus the professional fact-check index; filter by verdict and source
- No checks are published yet.

## Pricing

- [Pricing](https://beta.polygraphs.xyz/pricing): pay as you go in credits; a human-readable page
- [pricing.md](https://beta.polygraphs.xyz/pricing.md): the same prices as Markdown, generated from the pricing code

## For agents

- [Authenticated MCP endpoint](https://beta.polygraphs.xyz/mcp): Model Context Protocol over Streamable HTTP for a signed-in Polygraph account. Sign in with OAuth (dynamic client registration; metadata at [/.well-known/oauth-protected-resource](https://beta.polygraphs.xyz/.well-known/oauth-protected-resource)) or send `Authorization: Bearer pg_…`. Reads your checks and balance; with the check scope it can quote and run checks, which spend the account's credits. Connect steps per client: [Tools](https://beta.polygraphs.xyz/tools#mcp)
- [Developer API](https://beta.polygraphs.xyz/tools/api): JSON over HTTPS at `https://beta.polygraphs.xyz/api/v1` — quote, check, get a post or claim, re-verify, share, a changes feed. Authenticate with a `pg_` key from [Tools](https://beta.polygraphs.xyz/tools#keys) as `x-api-key` or `Authorization: Bearer`. Read keys read; read + check keys can spend credits.
- [OpenAPI 3.1](https://beta.polygraphs.xyz/api/v1/openapi.json): the developer API as a machine-readable spec
- [Public MCP endpoint](https://beta.polygraphs.xyz/api/mcp): read-only Model Context Protocol server over Streamable HTTP (JSON-RPC 2.0, POST). No authentication. Published rows only. Tools:
- `search_fact_checks`: full-text search over published Polygraph claims and the professional fact-check index; filter by verdict and source
- `get_claim`: one published claim by slug: verdict, confidence, summary, rated sources, carrying posts, history, plus schema.org ClaimReview
- `get_check`: one published post check by slug: the post, its verdict counts and every published claim on it
- [Public JSON](https://beta.polygraphs.xyz/api/public): `/api/public/search?q=`, `/api/public/claims/<slug>`, `/api/public/checks/<slug>`; the same data behind the public pages
- Public pages also register the three tools through WebMCP (`navigator.modelContext`) when the browser supports it.

## Policies

- [Methodology](https://beta.polygraphs.xyz/methodology): how claims are extracted, verified and rated
- [About](https://beta.polygraphs.xyz/about): who runs Polygraph
- [Privacy](https://beta.polygraphs.xyz/privacy)
- [Terms](https://beta.polygraphs.xyz/terms)