Citation Checker in ChatGPT
Check references and DOIs. The MCP server is https://citations.openkrill.app/mcp. No key. The steps below are only for ChatGPT. A call to check_references was checked against that server on 2026-10-01.
What this server answers
Paste a bibliography or a single reference and find out whether the papers are real. Ask "are these references real?", "check my bibliography", "verify this citation", "is this DOI correct?" or "has this paper been retracted?".
Citation Checker looks every reference up in Crossref, the DOI system (doi.org) and OpenAlex, which index the scholarly record, and gives each one a clear verdict: found, mismatch or not found.
A mismatch means a real paper exists but the reference gets something wrong, such as a DOI that belongs to another paper or a wrong year or author list; the real record is shown so the error is easy to fix. Not found means nothing matching exists, which for a bibliography entry often points to an invented or garbled citation.
It also reports whether a paper has been retracted, partially retracted, flagged with an expression of concern or corrected, from the notices that publishers and the Retraction Watch database register with Crossref.
It checks up to 10 references at a time. It compares bibliographic details only (title, authors, year, journal, DOI); it does not read papers or judge whether their claims are true. Books, reports, web pages and talks are often missing from the scholarly indexes, so a not found there is a prompt to check by hand, not proof.
It stores nothing about you: answers are cached for up to six hours, and the only lasting record is a daily count of calls per tool.
What it can do
- Checks whether the references in a bibliography are real papers
- Flags a DOI that belongs to a different paper than the reference describes
- Finds a wrong year or author list by comparing a reference with the real record
- Reports retractions, expressions of concern and corrections for a paper
- Looks up references that have no DOI by their title, authors and year
Tools
check_references, Check references and DOIs. Use this when the user asks "are these references real?", "check my bibliography", "verify this citation", "is this DOI correct?" or "has this paper been retracted?". Pass each reference as one string as written (authors, year, title, journal, DOI), or just a DOI or a title, up to 10 at a time. Looks each one up in Crossref, the DOI system and OpenAlex and returns a verdict per reference: found (a real record matches), mismatch (a real record exists but the DOI, title, authors or year differ; the real record is shown) or not_found (nothing matches, so it may be invented or garbled). Also returns the paper's retraction status (retracted, expression of concern, corrected) from Crossref. It checks bibliographic details only, not whether a paper's claims are true.
Add Citation Checker in ChatGPT
ChatGPT does not read a local config file. A custom MCP server is added in the product, and only after developer mode is on. These steps were checked against OpenAI's plugin connect guide and the ChatGPT MCP guide on 2026-10-01. Developer mode can be hidden by a workspace policy, so a Team or Enterprise admin may have to allow it first.
- Open ChatGPT settings, then Security and login, and turn on Developer mode.
- Open ChatGPT plugins and select the plus button.
- Enter a name such as "Citation Checker" and a one-line description of what you want it to answer.
- Under Connection, choose the public endpoint and paste
https://citations.openkrill.app/mcp. Include the/mcppath. Do not add a tunnel id: this server is already public. - Create the connection and review the tools ChatGPT lists. You should see
check_references. The feedback tools on the same server are optional and not required for the lookup. - Start a new conversation, add the connection from the tools menu, and ask: Check my bibliography and tell me which references are real
No API key and no OAuth client id are required. The server answers without a login. Calls are limited per network and per day, and a limit comes back as a tool error rather than a partial answer. If the tool list is stale after a server change, open the connection and select Refresh, then start a new conversation.
The ChatGPT desktop app, Codex CLI and IDE extension share a different config. In the desktop app, open Settings, then MCP servers, choose Add server, select Streamable HTTP, and paste the same URL. In ~/.codex/config.toml the equivalent is a table named mcp_servers.citations with url = "https://citations.openkrill.app/mcp". ChatGPT on the web does not read that file. A published directory listing is also a different path: this page is the developer-mode connection, not a claim that Citation Checker is already in the ChatGPT directory.
Treat the server as untrusted until you have read a few answers. A remote MCP server sees the arguments the model sends. Citation Checker is read-only and documents what it sends onward on the privacy page.
A call checked on 2026-10-01
A bare DOI is a valid reference string. The record is public in Crossref. The request below was posted to https://citations.openkrill.app/mcp as tools/call. HTTP 200. Source: the Citation Checker server, read 2026-10-01.
{
"method": "tools/call",
"params": {
"name": "check_references",
"arguments": {
"references": [
"10.1038/nature14539"
]
}
}
}- references. 1 returned
- references title. Deep learning
- references verdict. found
Repeat the call yourself if you need a newer reading. Cached answers expire. A rate limit is not a result: wait and try again. Nothing in the call is a ranking, a filing, or advice.