Marks every change

latexdiff is a Perl script that compares two LaTeX source files and produces a third LaTeX file with the changes marked up using two macros: \DIFadd{...} for insertions and \DIFdel{...} for deletions. When you compile that third file with pdflatex, the additions appear in blue and the deletions appear in red strikethrough. The ulem package handles the strikethrough.

It understands LaTeX

It is not a text diff. A plain diff tool would compare your files line by line and miss the LaTeX structure entirely — it would flag a renamed \section{} as a complete rewrite even if you only changed one word. latexdiff understands LaTeX. It diffs paragraphs, sentences, equations, and citations as separate units, and it leaves the document compilable on the other side.

Why researchers use it

This matters because most researchers use latexdiff for one of three reasons: tracking what changed between drafts when working with co-authors, generating a revision file for journal resubmission, or sanity-checking changes during a thesis revision pass. Many journals require authors to upload both a clean manuscript and a marked-up revision showing all changes — latexdiff is the standard way to produce that second file. None of these workflows work with a generic text diff.

Why run it online

The catch is installation. latexdiff ships with TeX Live and MiKTeX on most Linux and Mac setups, but Windows users almost always hit a wall — latexdiff is a Perl script, and Perl is not preinstalled on Windows. You end up installing Strawberry Perl, then pointing TeX Live at it, then dealing with path issues. Overleaf users hit a different wall: latexdiff is built into Overleaf's Track Changes feature, but that feature is gated behind their paid Premium plan. For a one-off comparison, neither path is worth the effort. That is the gap this tool fills — a free, online latexdiff that works in any browser, with no install and no subscription.

No. Perl runs server-side on our end. Paste LaTeX source or upload project ZIPs and get a result.

No. diff is a generic text comparison tool that does not understand LaTeX structure. latexdiff parses the LaTeX, then diffs at the paragraph and equation level, then writes a compilable LaTeX file with markup macros. The two are not interchangeable.

The most common cause is a missing ulem package on your local install. latexdiff adds \RequirePackage[normalem]{ulem} to the diffed file's preamble — if you do not have it, the compile fails on that line. Install it from your TeX distribution and the file will compile.

The second most common cause is template incompatibility. Some journal classes (elsarticle, acmart, sn-jnl) redefine commands that conflict with \DIFadd and \DIFdel. Switch the subtype option to SAFE and try again.

Yes. Download both project versions from Overleaf (Menu → Download → Source) and upload the ZIPs directly. Multi-file projects using \input{} and \include{} are supported.

For comparing two completed versions, yes. Overleaf Track Changes is a live, interactive editor on the Premium plan. This tool generates a static diff of two LaTeX files or complete project ZIPs in seconds for free

Yes, free. It runs on a small server-side service and serves a few thousand requests a month comfortably. No signup, no paid tier.