Questions it 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 or "has this paper been retracted?".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It also reports whether a paper has been retracted, partially retracted, flagged with an expression of concern or corrected, from the notices that publishers and the Retraction Watch database register with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.
Short questions this server answers, each with a direct answer: Check references and DOIs for real papers.
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 or "has this paper been retracted?".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 Claude
Claude connects to a remote MCP server as a custom connector. The connection is made from Anthropic's cloud, not from your laptop, so the server must be on the public internet. Citation Checker is. These steps were checked against Claude's custom-connector article (updated 2026-08-11) and the Claude Code MCP docs on 2026-10-01.
On a Pro or Max plan:
- Open Customize, then Connectors.
- Select the plus button, then Add custom connector.
- Paste this URL. Leave Advanced settings empty: this server does not need an OAuth client id or secret.
https://citations.openkrill.app/mcp - Select Add. The connector is yours. Anthropic has not reviewed it, and it is not a Directory listing.
- In a conversation, open the plus button, then Connectors, and enable Citation Checker. Ask: Check my bibliography and tell me which references are real
On Team and Enterprise, an Owner adds the connector first at Organization settings, then Connectors, then Add, then Custom, then Web, and pastes the same URL. Members then connect it from Customize. A Free plan can add one custom connector.
In Claude Code, add it from the project directory:
claude mcp add --transport http citations https://citations.openkrill.app/mcpThat writes a local or user config. A JSON entry needs "type": "http" (or streamable-http) plus the url. An entry with a url and no type is skipped. Confirm with claude mcp get citations. The tools you should see are check_references.
If Claude tries to fetch https://citations.openkrill.app/mcp from its code sandbox and reports HTTP 403, the block is Claude's sandbox network allowlist, not this server. The sandbox proxy answers 403 with x-deny-reason: host_not_allowed for every host outside the allowlist. Use the connector above instead: connector calls come from Anthropic's cloud and do not pass the sandbox proxy. To let the sandbox reach it as well, an Owner adds citations.openkrill.app under Settings, then Capabilities, then Additional allowed domains.
Enable the connector only in conversations that need it. Claude can call the tools while you work, including during research, so turn off any tool you do not want invoked. Citation Checker does not write to your accounts. It still receives the arguments of each call. Read the privacy page before you paste anything that is not public.
If it does not work
The tool does not show up
In Claude, enable the connector in the conversation from the plus button, then Connectors. In Claude Code, run claude mcp list from the same directory you added it in, then start a new session: a running session does not load a new server.
429 or rate_limited
Each server takes 60 calls a minute from one network, and some tools take fewer. Past that the call comes back as a tool error that starts with rate_limited: wait a minute and ask again. daily_limit means the server reached its shared daily cap, which resets at 00:00 UTC. A limit is not an answer, so do not read it as no results. For higher limits, ask support@openkrill.app for a key.
JSON entry has no type
Claude Code skips an entry in .mcp.json that has a url but no type. Add "type": "http" next to the url, or add the server with claude mcp add --transport http, which writes the type for you. The VS Code entry needs the same type field. Cursor and Pi read the url alone.
A call checked on 2026-10-17
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 2026-10-17.
{
"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.
Using it in production
Nothing to install and nothing to run: no package, no Python or Node.js version and no environment variable. Citation Checker runs on our servers, and your client only needs the URL https://citations.openkrill.app/mcp.
| Rate limit | 60 tool calls a minute from one network. initialize and tools/list do not count. |
|---|---|
| Daily cap | 25000 tool calls a day per server, shared by every caller. It resets at 00:00 UTC. |
| At a limit | The call comes back as a tool error that starts with rate_limited (wait a minute) or daily_limit (try after 00:00 UTC), never as a partial answer. |
| Key | None. Do not add an Authorization header or a key field. |
| Higher limits | Email support@openkrill.app with the server name, the calls a day you expect and what they are for. We answer within 1 business day. |
| Freshness | Some answers come from a short cache. Each guide shows the date of its checked call; repeat a call when you need a newer reading. |
| Uptime | Scheduled test calls check the servers through the same endpoint. There is no SLA yet. |
| Data | What each server receives and keeps is on the privacy page. |
Use it in other apps
- Citation Checker in ChatGPT
- Citation Checker in Cursor
- Citation Checker in VS Code
- Citation Checker in Pi
Roles that use Citation Checker
Frequently asked questions
How do I install the Citation Checker MCP server in Claude?
In Claude, open Customize, then Connectors, choose Add custom connector and paste https://citations.openkrill.app/mcp. In Claude Code, run claude mcp add --transport http citations https://citations.openkrill.app/mcp. No restart is needed for either.
Do I need an API key to run Citation Checker in Claude?
No. This server takes no API key. For higher limits, email support@openkrill.app with the server name (Citation Checker), the calls a day you expect and what they are for. We answer within 1 business day.
What should I do if Citation Checker does not connect in Claude?
Check that the connector URL ends in /mcp and that Advanced settings are empty. In Claude Code, run claude mcp get citations; a JSON entry with a url but no type is skipped, so add type http.