Bibcop: Style Checker of BibTeX .bib files

This LaTeX package checks the quality of your .bib file and emits warning messages if any issues are found. You may also like biblint and biblatex-check tools — they do almost the same but from the command line.

Read this blog post, in order to understand the motivation behind this package.

First, install it from CTAN and then use in the preamble (if you use BibTeX, for example):

\documentclass{article}
\usepackage{bibcop}
\begin{document}
\bibliographystyle{plain}
\bibliography{main}
\end{document}

You can also add it as a GitHub Action to your GitHub repository, with the help of bibcop-action.

Otherwise, you can download bibcop.sty and add to your project (together with bibcop.pl!).

You can also download bibcop.pl and use it as a command line tool to check your .bib files and to auto-fix them (you should have Perl installed):

perl bibcop.pl --fix main.bib > fixed.bib

This command will read the main.bib file and create fixed.bib, which will have the fixed and properly formatted content (well, to some extent). Be careful, all comments will be removed.

You can also make changes inline, not creating a new file:

perl bibcop.pl --fix --in-place main.bib

If you install the package using tlmgr, you should be able to use bibcop directly, without the necessity to mention Perl:

tlmgr install bibcop
bibcop --help

How to use as pre-commit hook

If you use pre-commit, simply add this to your config:

-   repo: https://github.com/yegor256/bibcop
    rev: 0.0.32
    hooks:
    -   id: bibcop
        args: []

Architecture

The core logic resides in a single Perl script, bibcop.pl, which parses .bib files and runs all checks. The LaTeX package (bibcop.sty) is a thin wrapper that invokes this script at compile time via the \iexec macro (from iexec), using TeX's --shell-escape mechanism, by hooking into \bibliography and \addbibresource. This is the key differentiator from tools like biblint and biblatex-check, which run only from the command line: bibcop runs automatically during every LaTeX compilation without a separate invocation step.

Check functions follow a naming convention: every Perl subroutine whose name matches check_* is auto-discovered at runtime by introspecting the package symbol table inside process_entry(). Adding a new check requires only a new sub check_* function with no registration step, so a defined check can never be silently skipped.

Only six BibTeX entry types are permitted: @article, @book, @incollection, @inproceedings, @misc, and @phdthesis, each with a fixed allowlist of tags in %blessed. Tags outside the allowlist are an error. This closed-world model is stricter than tools such as biblatex-check, which tolerate arbitrary or unknown tags.

The BibTeX parser in entries() is a hand-written, character-by-character state machine that depends only on Perl's built-in POSIX and File::Basename modules. BibTeX::Parser and similar CPAN libraries were deliberately avoided so that installing bibcop from CTAN requires no separate Perl module installation.

The script detects at runtime whether it is invoked as a CLI tool or loaded as a Perl module via require, by inspecting basename($0). This lets the same file serve both the LaTeX package backend and the standalone command-line interface without any code duplication.

The package source and documentation coexist in a single .dtx file following the DocStrip convention; the .sty is extracted by l3build via bibcop.ins. Tests split into two suites: l3build testfiles cover the LaTeX integration layer, while perl tests.pl runs Perl-level unit tests directly.

Beyond reporting, the --fix flag activates an auto-correction mode where dedicated fix_* subroutines reformat field values: author names, page ranges, capitalization, and Unicode-to-TeX transliteration. This repair capability is absent from both biblint and biblatex-check.

How to Contribute

If you want to contribute yourself, make a fork, then create a branch, then run l3build ctan in the root directory. It should compile everything without errors. If not, submit an issue and wait. Otherwise, make your changes and then run l3build ctan again. If the build is still clean, submit a pull request.

If you want to add a new check, add it as a Perl subroutine to the bibcop.pl file. Don't forget to add a test to one of the test files that stay in the perl-tests/ directory. When ready, run this, in order to check that all tests pass:

perl tests.pl

You should see the GREAT! message.

Copyright (c) 2022-2026 Yegor Bugayenko, MIT License