What the checker looks at
DOIs
Every DOI is resolved in Crossref, the registry publishers deposit their records with. The checker compares the record's title, first author and year with what your entry says.
Titles and authors
An entry without a DOI is searched in Crossref and then in OpenAlex, an open index of scholarly work. A match needs the title words and the first author to agree.
ISBNs
Books with an ISBN are checked in Open Library, and the record's title has to match the title in your reference.
Web links
Web pages are not in academic indexes, so the checker opens each address and tells you if it is gone. You still check the author and date on the page.
What each result means
Why reference lists go wrong
AI chatbots. A language model writes a reference the way it writes any sentence: as the most likely sequence of words. The result often has a real journal, plausible authors and a DOI in the right format that resolves to nothing, or to a different paper. Our article on fake AI citations goes through the research on how often this happens and what the invented entries look like.
Copying from other papers. References copied from another paper's bibliography carry its mistakes with them, and the details drift each time: a year off by one, a volume number from the preprint, a page range from a different version.
Typos in identifiers. One wrong character in a DOI sends the reader to an error page or to someone else's work. Nobody notices until a marker or a reviewer clicks the link.
Link rot. Web pages move and disappear. A link that worked when you read the page can return 404 by the time your paper is marked.
What a clean result does not prove
A verified entry means the work exists and your details match its record. It does not mean the source supports the sentence you cite it for. Chatbots often attach a real paper to a claim it never makes, and no index can catch that. Open every source you rely on and find the passage.
The reverse also holds. “No matching record” is a reason to look, not proof of fraud: conference papers, government reports, theses and older books are often missing from the indexes.
Free and PRO
The free check covers the first 5 references of any list, 5 times a day, with the full result for each one. FreeCitation PRO checks up to 150 references at once with no daily limit, and gives you the report as a CSV file or as plain text to keep with your draft. PRO also includes unlimited citations in all ten styles, footnotes and in-text forms, and Word, BibTeX and RIS export.
When the checker finds the right record, Cite this record opens it in the citation generator, so you can replace a broken entry with a correct one in your style.
Your list stays yours
To check an entry, its text is sent to Crossref, OpenAlex or Open Library as a search, and the answer comes straight back to your browser. FreeCitation does not save the list. We store only the number of entries checked and the number verified, which is what the daily limit needs. The privacy policy has the details, and the methodology page explains where every record comes from.
Questions
How does the reference checker know a citation is fake?
It does not call anything fake. It looks each entry up in Crossref, OpenAlex and Open Library and reports what it finds: a DOI no publisher registered, a DOI that belongs to another paper, or no record at all for that title and author. Those are the patterns invented references leave, but a typo or an unindexed report can cause them too, so the result tells you which entries to look at by hand.
Which citation styles does it read?
Any of them. It does not parse the style, it pulls out the DOI, ISBN, web address, year, title and first author, so APA, MLA, Chicago, Harvard, IEEE, Vancouver, AMA, Turabian, Oxford and OSCOLA lists all work, numbered or not.
How many references can I check for free?
The free check covers the first 5 references of a list, 5 times a day. FreeCitation PRO checks up to 150 references at once with no daily limit, and gives you the report as a CSV file or as text to copy.
Do you keep my reference list?
No. The list is sent to Crossref, OpenAlex and Open Library to look each entry up, and the results come straight back to your browser. We store only how many entries were checked and how many were verified, so the free limit works.
Does a verified result mean I can use the source?
It means the work exists and your details match its record. It does not mean the source says what your sentence claims. AI chatbots often cite real papers for claims those papers never make, so open each source you rely on.