# Citation Checker

Check that references are real and that a paper was not retracted. It is free, with no sign-up and no key.

## What it does

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 or "has this paper been retracted?".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It also reports whether a paper has been retracted, partially retracted, flagged with an expression of concern or corrected, from the notices that publishers and the Retraction Watch database register with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.

- 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

## Who it is for

Anyone who asks an AI assistant a question like this one: “Are these references real?”

Roles that use it at work: Researcher, Editor.

## Price

Citation Checker is free to use. There is no sign-up, no account and no API key. Calls are limited to 60 calls a minute per network and 5000 calls a day per server, shared by all callers. Repeat questions are answered from a cache.

## Tools it offers

- `check_references`: Check references and DOIs

## Connect

The MCP server is `https://citations.openkrill.app/mcp` (streamable HTTP). It needs no key.

Claude Code, in one command:

```
claude mcp add --transport http citations https://citations.openkrill.app/mcp
```

Hermes Agent, in one command that answers its two setup questions (no key, enable all tools):

```
printf 'n\ny\n' | hermes mcp add citations --url https://citations.openkrill.app/mcp
```

Or add these lines to `~/.hermes/config.yaml`, under an existing `mcp_servers:` key if the file has one. Start a new Hermes session after either step.

```
mcp_servers:
  citations:
    url: https://citations.openkrill.app/mcp
```

Any other agent: give it this page's Markdown address, `https://tools.openkrill.app/tools/citations.md`, and ask it to connect Citation Checker.

Install guides, each checked with a real call: [Citation Checker in ChatGPT](https://tools.openkrill.app/integrations/citations/chatgpt), [Citation Checker in Claude](https://tools.openkrill.app/integrations/citations/claude), [Citation Checker in Cursor](https://tools.openkrill.app/integrations/citations/cursor), [Citation Checker in VS Code](https://tools.openkrill.app/integrations/citations/vscode), [Citation Checker in Pi](https://tools.openkrill.app/integrations/citations/pi).

## Job recipes for agents

Step-by-step recipes that walk an agent through a job with this server's tools:

- Check references and DOIs, with `check_references`

[Download the recipes as SKILL.md](https://tools.openkrill.app/skills/citations-jobs/SKILL.md). Save it as `citations-jobs/SKILL.md` in your agent's skills folder. A connected MCP client gets the same recipes from `prompts/list` on the gateway, `https://api.openkrill.app/gateway/mcp`.

It is listed under Research and public facts in the [full tool list](https://tools.openkrill.app/tools). The same facts in plain text are in [llms.txt](https://tools.openkrill.app/llms.txt).

Source: the Citation Checker listing, version 1.0.2. As of 2026-10-18.