LaTeX Citation Error Checker
Paste your .tex and .bib content below. Instantly find undefined citations, missing bibliography entries, and mismatched cite keys.
Common LaTeX citation errors
Undefined citation [?]
LaTeX shows [?] when a \cite{} key doesn't match any entry in your .bib file. Usually a typo or missing entry.
Citation on input line X
LaTeX log warning. Means you ran BibTeX before the .aux file was updated. Run compile twice.
Empty bibliography
The \bibliography{} command points to a .bib file that is empty, missing, or misnamed.
\cite vs \citep vs \citet
Using \cite{} with natbib can produce unexpected output. \citep gives (Author, year), \citet gives Author (year).
Duplicate bib keys
Two entries with the same key — BibTeX uses the last one silently. Can cause wrong citations.
Multiple citations [?,?]
\cite{a,b,c} requires all three keys to be defined. One missing key makes all show as [?] in some engines.
Check citations live as you write
Bibby AI highlights undefined citations in real-time — no more compile-check-fix loops.