I'm a master's engineering student. I wrote my thesis in Overleaf and it was fine until I wanted git sync, which sits behind the paywall. I didn't want to pay a subscription for something that should just work, so in my free time I built the editor I wanted: open a tab, write LaTeX, get a PDF, and the files stay in a folder on my disk.

TeXbrain is a static site. There is no backend. pdfTeX is compiled to WebAssembly (the SwiftLaTeX engine) and runs in your browser. The editor reads and writes your real project folder through the File System Access API, so you can keep using git, your local TeX install or any other editor on the same files. Git is built in through isomorphic-git for people who would rather not touch a terminal: clone, branch, commit, push, pull. No accounts, no analytics, and it works offline after the first load.

Try it out: https://tex.swimmingbrain.dev (Chromium browsers get direct folder access, Firefox and Safari fall back to a virtual filesystem)

Source: https://github.com/swimmingbrain/texbrain (MIT. The pdfTeX engine is EPL 2.0 / GPL 2.0 with Classpath exception, see THIRD_PARTY_LICENSES)

The part I'm happiest with is package loading. The engine itself is 1.8 MB. When it asks for a file it doesn't have, a service worker intercepts the request and resolves it through a chain: Cache Storage first, then a small bundled subset, then a TeX Live tree mirrored on jsDelivr (pinned to a commit that matches the engine's TeX Live 2020 era, looked up through its file index), then a SwiftLaTeX style server as a last resort. Every file is fetched at most once. After the first successful compile the core subset is prefetched in the background so the offline story actually holds. Before this, anything outside the bundled set died with "file not found". Now memoir, KOMA, abntex2 and most of CTAN work on first use. Only file names go over the network, never document content.

A few smaller things: only changed files are sent to the engine between compiles, aux files persist so the second pass only runs when the log asks for it, PDF pages render lazily with pdf.js, and a missing image gives you a placeholder instead of a failed build.

What it can't do, so you don't get disappointed:

- it's pdfTeX only. No XeTeX or LuaTeX, so fontspec and polyglossia won't work.

- Bibliographies are the roughest edge. There is no bibtex or biber in the engine. For biblatex documents the app parses your .bib and generates a plain thebibliography, so you get references but your citation style is ignored. A real bibtex in WASM is the next thing on my list.

- Packages are pinned to the TeX Live 2020 era to stay coherent with the engine's format file.

- Git push and pull go through a CORS proxy because browsers can't speak the git protocol directly. The default is the isomorphic-git project's public proxy and you can point it at your own.

Who this is for: people on a work laptop, a Chromebook or a university lab PC where installing TeX Live isn't an option, and people who don't want to maintain a TeX install at all. If you already have a local setup you like, keep it. This isn't trying to replace it.

A few people have used it for their thesis so far and their bug reports were then most of the summer's work. One of them needed abntex2 with Brazilian babel, which surfaced a version mismatch I would never have hit on my own. The first outside PR landed recently. If something doesn't compile for you, an issue with the package name is the most useful thing you can send me.

Show HN: TeXbrain, a LaTeX editor that runs pdfTeX in the browser via WASM