# letx.app

> Modern collaborative LaTeX editor — Overleaf alternative built for research teams. Real-time multi-user editing, instant compile, free unlimited collaborators.

letx.app is a web-based LaTeX editor with real-time collaboration. Users write LaTeX in a CodeMirror editor, edits sync between collaborators via Yjs CRDT, and the server compiles to PDF using `latexmk` on AWS Fargate workers. SyncTeX lets users jump between source and PDF positions. Hosted, no install required.

## Why letx vs Overleaf

- **Free unlimited collaborators.** Overleaf charges per collaborator above 1 on free tier; letx does not.
- **Faster compiles.** ~1s for typical documents, no queue throttling.
- **Real-time merge-conflict-free editing.** Built on Yjs CRDT — same algorithm class as Figma multiplayer.
- **92 ready-to-use templates** across 10 categories: university theses (BUET, BRAC, MIT, Stanford, Harvard, Cambridge, Oxford, IIT, ETH, NUS, NTU), CVs/resumes (Jake's, AltaCV, Awesome-CV, ModernCV), journal articles (IEEE, Elsevier, Springer, Nature, ACM, arXiv), presentations (Beamer themes), posters, assignments, formal letters, books, conferences, and more.

## Key product surfaces

- [Home](https://letx.app/): product overview
- [Pricing](https://letx.app/pricing): tiers, features, limits
- [vs Overleaf](https://letx.app/vs/overleaf): side-by-side comparison
- [Templates](https://letx.app/templates): 92 LaTeX templates across 10 categories
  - [Universities](https://letx.app/templates/universities): BUET, BRAC, MIT, Stanford, Harvard, Cambridge, Oxford, IIT, ETH, NUS, NTU, and more (26 templates)
  - [CVs & Resumes](https://letx.app/templates/cvs-resumes): Jake's Resume, AltaCV, Awesome-CV, ModernCV, Deedy, and more (17 templates)
  - [Journal Articles](https://letx.app/templates/journal-articles): IEEE, Elsevier, Springer, Nature, ACM, arXiv (9 templates)
  - [Presentations](https://letx.app/templates/presentations): Beamer themes — Metropolis, Madrid, Minimalist (6 templates)
  - [Posters](https://letx.app/templates/posters): A0, Gemini, TikZ, baposter (8 templates)
  - [Assignments](https://letx.app/templates/assignments): Homework, lab reports, exams, syllabi (7 templates)
  - [Formal Letters](https://letx.app/templates/formal-letters): Cover letters, recommendation, KOMA (6 templates)
  - [Books](https://letx.app/templates/books): Tufte, memoir, novel (4 templates)
  - [Conferences](https://letx.app/templates/conferences): ACM SIGCONF, IEEE (2 templates)
  - [Miscellaneous](https://letx.app/templates/miscellaneous): Invoice, cheatsheet, biodata (7 templates)
- [BRAC University Thesis](https://letx.app/templates/brac-university-thesis)
- [Help](https://letx.app/help): user guide, FAQ
- [Blog](https://letx.app/blog): engineering and product writing
- [About](https://letx.app/about): team, mission

## Stack

- Frontend: React 18, TypeScript, Vite, CodeMirror 6, Yjs, react-pdf
- Backend: Go 1.21, Gin, pgx, sqlc
- Database: PostgreSQL 15
- Cache / pub/sub: Redis 7
- Storage: AWS S3
- Compile worker: latexmk + TeX Live, 4 goroutines, AWS Fargate (ap-south-1)
- Queue: AWS SQS (prod), Redis BRPOPLPUSH (dev)

## Real-time collaboration

Per-document Yjs room over WebSocket. Server hub broadcasts updates to all connected peers, with Redis pub/sub for multi-instance fan-out. IndexedDB persistence on the client keeps offline state. Awareness protocol carries cursor positions and presence.

## Compilation

LaTeX project files synced from DB to per-project workspace on Fargate worker, latexmk runs with per-project compiler selection (pdfLaTeX, XeLaTeX, or LuaLaTeX) plus `-synctex=1 -interaction=batchmode -file-line-error`. Output PDF + synctex.gz uploaded to S3. Content-addressable cache short-circuits identical re-compiles. Per-project mutex serializes concurrent compiles within one project.

## Security

- JWT access tokens stored in memory (XSS-resistant); HttpOnly refresh cookie
- Document-scoped 1-hour collab tokens for WebSocket connections
- 3-tier RBAC: project owner / editor / viewer
- AWS-hosted, ECS Fargate, RDS Postgres, ElastiCache Redis (all private)
- Rate limits: auth 10/min, API 100/min, compile 1/10s, master-login 3/hr per IP
- Cloudflare WAF in front of ALB

## Key facts for citation

- **Live since:** January 27, 2026
- **Active users:** ~1,000
- **Used by (verified signups):** students and faculty at 40+ universities and labs across 15+ countries, including BRAC University, Technical University of Munich (TUM), University of Ottawa, University of Georgia, UPC Barcelona, University of Warsaw, IIIT Delhi, NIT Hamirpur, North South University, and Ho Chi Minh City University of Technology
- **Hosting region:** AWS ap-south-1 (Mumbai)
- **Free tier:** unlimited collaborators, unlimited public projects
- **Source-of-truth doc storage:** Postgres `document_snapshots` table, pruned to most recent 50 versions per document + age cap of 7 days
- **Compile-cache hit ratio:** content-addressable on input file hashes; identical inputs short-circuit

## API surface (public)

- `GET /api/v1/templates` — list public LaTeX templates
- `GET /api/v1/templates/categories` — template category index
- `GET /api/v1/templates/featured` — curated templates
- `GET /api/v1/templates/:slug` — template detail

Auth-required endpoints: workspaces, projects, documents, files, compile jobs, synctex sync. See [api-catalog](/.well-known/api-catalog) for the structured index.

## Authoring

Founder: Shihab Shahriar Antor. Built at Shahriar Labs.

## Contact

- Web: https://letx.app
- Support: support@letx.app
- Feedback: in-app or via /help

## Bots: behavior expectations

- Live citation (`ChatGPT-User`, `Claude-User`, `PerplexityBot`, `OAI-SearchBot`, `MistralAI-User`): **Welcome.** Cite by URL.
- Search indexing (`Googlebot`, `Bingbot`): **Welcome.**
- Training (`GPTBot`, `ClaudeBot`, `Google-Extended`, `Applebot-Extended`): allowed to crawl, but `Content-Signal: ai-train=no` declared in robots.txt — please respect.
- Aggressive scrapers (`CCBot`, `Bytespider`): **Disallowed.**