A browser-only web app for comparing two LaTeX sources and producing a tracked-changes file — the same kind of output you get from the classic latexdiff command-line tool, but without installing Perl or uploading your manuscript anywhere.

Paste or drop your old and new .tex files, click Generate, then copy or download diff.tex and compile it locally. Everything runs on your machine inside the tab.

Live demo: https://latexdiff.web.app/

• Why this exists
• Features
• How to use (workflow)
• How it works
• Requirements
• Development
• Build and deploy
• Project layout
• Limitations
• Acknowledgements
• License

Academic writing often means juggling two versions of the same paper — e.g. an old main.tex and a revised main.tex from a co-author, backup, or git checkout. The standard tool for visualising changes in LaTeX is latexdiff by F. Tilmann: it compares two .tex files and emits a third file marked up with \DIFadd{…} and \DIFdel{…} (and related macros) so you can compile a PDF with visible insertions and deletions.

That usually means:

1. Installing Perl and latexdiff (or using a TeX distribution that includes it).
2. Running a terminal command on files that may live on another machine.

LaTeX Different wraps the same diff engine in a simple three-column UI and runs it via WebAssembly + WebPerl in the browser. Your sources never leave your computer.

Typical paper workflow:

1. Old column — Paste or drop the previous version of your manuscript (often main.tex from an older draft or branch).

2. New column — Paste or drop the revised version (the updated main.tex).

3. Click Generate and wait for the WebPerl engine (first time may take a minute while assets download).

4. Review the result in Tracked Changes — use Preview to see coloured additions/deletions, or Source for raw LaTeX.

5. Copy or Download the output, save it as diff.tex (or another name) in the same project folder as your figures, bibliography, and \input files.

6. Compile diff.tex, not main.tex:

   pdflatex diff.tex
   # or latexmk, Overleaf “Recompile” on diff.tex, etc.

Important: main.tex is unchanged. Only the generated diff file contains \DIFadd / \DIFdel markup. Compiling main.tex will not show tracked changes.

Use Load demo in the header to try a small built-in pair without your own files. Open the tutorial (graduation-cap icon) or about (ⓘ) in the toolbar for the same guidance inside the app.

┌─────────────┐     ┌──────────────────┐     ┌─────────────────┐
│  Old .tex   │     │  wasm-latex-tools │     │  diff.tex       │
│  New .tex   │ ──► │  WebPerlRunner    │ ──► │  (\DIFadd/      │
│  (browser)  │     │  + latexdiff.pl   │     │   \DIFdel…)     │
└─────────────┘     └──────────────────┘     └─────────────────┘

• wasm-latex-tools bundles latexdiff.pl and runs it through WebPerl (Perl 5 compiled to WebAssembly) inside a hidden iframe (perlrunner.html).
• Static assets (emperl.wasm, emperl.data, Perl scripts) live under public/core/ and are copied on npm install via scripts/copy-assets-lite.cjs (texfmt omitted to save ~2 MB).
• The UI is Vite 6 + TypeScript, no framework — vanilla HTML/CSS/TS modules.

• Node.js 18+ (for development and building only)
• A modern browser with WebAssembly: Chrome, Firefox, Safari, or Edge
• For the PDF: a local LaTeX installation (TeX Live, MiKTeX, Overleaf, etc.) — this app does not compile PDFs

git clone https://github.com/jingjie00/latexdiff-ui.git
cd latexdiff-ui
npm install          # copies WebPerl + latexdiff assets into public/core/
npm run dev          # http://localhost:5173

postinstall runs node scripts/copy-assets-lite.cjs, which invokes wasm-latex-tools’s copy script and removes unused texfmt assets.

npm run build

Deploy the dist/ directory to any static host. Paths use Vite base: "./" so relative URLs work on subpaths.

GitHub Actions workflows build dist/ and deploy with the Firebase CLI:

• .github/workflows/firebase-hosting-merge.yml — deploy on push to main
• .github/workflows/firebase-hosting-pull-request.yml — preview channels for PRs

Local Firebase project id: latexdiff (see .firebaserc). Hosting serves the dist/ folder (firebase.json → "public": "dist").

After each deploy, the page footer shows built with the date/time in 24-hour GMT from when npm run build ran in CI. Use it to confirm the live site matches your latest GitHub push.

Hosting tips for WebPerl:

• Ensure core/webperl/* and core/perl/* are served (they are copied into dist/ from public/).
• Enable gzip/brotli for .wasm and .data files to speed first load.
• firebase.json sets Content-Type: application/wasm for .wasm files.

GitHub Pages, Netlify, Cloudflare Pages, etc. — upload dist/ as the site root. If you use a project-site subpath, set Vite base to match (e.g. base: '/latexdiff-ui/').

latexdiff-ui/
├── index.html              # App shell
├── src/
│   ├── main.ts             # Wiring, Generate, demo
│   ├── runner.ts           # WebPerl load + progress
│   ├── column.ts           # Drag-drop columns
│   ├── diff-highlight.ts   # Preview highlighting
│   ├── options-panel.ts    # Collapsible latexdiff options
│   ├── popover.ts          # Tutorial / About popovers
│   └── …
├── public/core/            # Generated by postinstall (gitignored)
│   ├── webperl/            # WASM runtime (~15 MB)
│   └── perl/               # latexdiff.pl, etc.
├── samples/                # demo-old.tex, demo-new.tex
├── scripts/copy-assets-lite.cjs
└── firebase.json

• Bundled latexdiff version comes from wasm-latex-tools, not your system TeX Live — options and behaviour follow that bundle.
• --flatten only inlines \input/\include when those files are available inside the WASM filesystem; for typical single-file main.tex pairs, leave flatten off.
• First visit downloads large WASM assets into a service worker cache (sw.js); repeat visits load from cache (same origin). Slow first loads show progress in the status bar.
• Very large .tex files may be slow or hit browser memory limits.
• Complex packages — same caveats as desktop latexdiff (see the manual).
• This app does not replace latexdiff-vc, latexrevise, or citation-aware wrappers like latexdiffcite.

This project is a thin UI on top of excellent existing tools. Credit belongs to their authors and communities.

• latexdiff — F. Tilmann. Compares two LaTeX files and marks significant differences. Distributed on CTAN; licensed under GPL-3.0.
  Manual: latexdiff-man.pdf

• wasm-latex-tools — Packages latexdiff (and related Perl tools) for in-browser use via WebPerl. AGPL-3.0 — review their license if you redistribute a hosted build.
• WebPerl — Perl 5 compiled to WebAssembly (Emscripten), enabling latexdiff.pl to run without a native Perl install.

• Algorithm::Diff (and related diff machinery used inside latexdiff) — see upstream latexdiff documentation and CPAN.
• Vite, TypeScript — build tooling.

• latexdiff-vc — version-control wrappers (git, svn, …)
• latexrevise — accept/reject changes in diff output
• git-latexdiff — git-focused wrapper
• latexdiffcite — improved citation diffing

• LaTeX Different (this repository) — UI and integration by Tan Jing Jie.

If you use this app in academic work, please cite the original latexdiff paper/package as appropriate for your field, and consider starring or contributing to ftilmann/latexdiff and TeXlyre/wasm-latex-tools.

MIT License (this repository’s own source: src/, index.html, etc.):

Copyright (c) Tan Jing Jie

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

When you deploy a hosted copy, you are distributing a build that includes AGPL/GPL components — ensure your deployment complies with those licenses (source offer, attribution, etc.).

• Author: Tan Jing Jie
• Issues and contributions: github.com/jingjie00/latexdiff-ui/issues