LaTeX Citation Error Checker

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Citation analysis

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LaTeX shows [?] when a \cite{} key doesn't match any entry in your .bib file. Usually a typo or missing entry.

Fix: match key exactly, case-sensitive

LaTeX log warning. Means you ran BibTeX before the .aux file was updated. Run compile twice.

Fix: pdflatex → bibtex → pdflatex → pdflatex

The \bibliography{} command points to a .bib file that is empty, missing, or misnamed.

Fix: check \bibliography{filename} matches filename.bib

Using \cite{} with natbib can produce unexpected output. \citep gives (Author, year), \citet gives Author (year).

Fix: use \citep / \citet with natbib packages

Two entries with the same key — BibTeX uses the last one silently. Can cause wrong citations.

Fix: each @entry needs a unique key

\cite{a,b,c} requires all three keys to be defined. One missing key makes all show as [?] in some engines.

Fix: verify each key in \cite{a,b,c} individually

Bibby AI highlights undefined citations in real-time — no more compile-check-fix loops.