The check every cited AI answer needs before you rely on it. A citation that looks complete and points to nothing costs a correction, a retraction or a sanction. Metis Check asks the registries that issue each identifier whether it exists and what it says. DOI, PubMed, arXiv, ORCID, ROR, ISBN, LEI, ISIN, CUSIP, SEC CIK, EIN, NPI, UK company numbers, domains and more. Each identifier comes back in exactly one of four states: settled true, settled false, not decidable (a person decides) or unreachable (a delay, not evidence). Every check ends in a signed report with its own id, a PDF and a recheck button anyone can press.
By Metis Foundry. One account covers ChatGPT, Codex, Claude, Claude Code, Cursor and VS Code. Every account starts with 5 checks a month; plans.
A real report: three identifiers settled true, one settled false. Open it and press Recheck.
| Client | How |
|---|---|
| Claude (web, desktop, mobile) | Settings → Connectors → add a connector by URL: https://mcp.metisfoundry.com/mcp. Once Metis Check is listed in the connectors directory, choose it there. |
| Claude Code | /plugin marketplace add MetisFoundry/metis-plugins then /plugin install metis-check@metis, or claude mcp add --transport http metis-check https://mcp.metisfoundry.com/mcp |
| Codex CLI | codex plugin marketplace add MetisFoundry/metis-plugins then codex plugin add metis-check@metis |
| ChatGPT | The Metis Check plugin is submitted to the OpenAI directory. Until it is listed: Settings → Connectors → add by address https://check-api.metisfoundry.com/mcp/check |
| Cursor | Add to Cursor |
| VS Code | Add to VS Code (web redirect), or code --add-mcp '{"name": "metis-check", "type": "http", "url": "https://check-api.metisfoundry.com/mcp/check"}' |
| Any MCP client | Remote server https://check-api.metisfoundry.com/mcp/check (OAuth sign-in; a free account is created on first connection). Registry name com.metisfoundry/metis-check. |
Sign in or create a free Metis account when the client asks.
The prompt asks Metis Check to check four references, one of them invented. The invented one comes back settled false, with the registry that said so.
- Four states, nothing hidden: settled true, settled false, not decidable, unreachable, and a not-checked list with the reason for each.
- A report that rechecks without Metis: every line carries the registry query and the SHA-256 of the registry's answer; signed JSON and a PDF.
- Shareable: anyone with the link can open the report and press Recheck; the registries are asked again, live.
- Private: passages are never stored, only the identifiers, their positions and a hash. Metis never asks for conversation history.
- Honest scope: Metis Check establishes that an identifier is registered and what the registry says. It does not decide whether a paper supports a claim.
Free: 5 checks a month. Pro: $29 a month (or $276 a year), 2,000 checks, case law included. Team: $249 a month (or $2,388 a year), 15,000 checks, 5 seats. Checks that cannot be settled cost nothing. Details: https://check-api.metisfoundry.com/check/plans
.agents/plugins/marketplace.json— Codex marketplace (metis); plugin inplugins/metis-check.claude-plugin/marketplace.json— Claude Code marketplace (metis); plugin manifest inplugins/metis-check/.claude-pluginserver.json— official MCP Registry manifestPUBLISH.md— how the listings are published
hello@metisfoundry.com. Proprietary: the files in this repository are not open source. You may install and use them, unmodified, with the Metis Check service (LICENSE, NOTICE.md).