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Hlool PDF
An elegant PDF stamping workbench.
Stamp, seam-seal and batch-process PDFs right in the browser — no upload needed.
Key facts
- Licence
- MIT
- Type
- Open-source web app
- Stack
- Go · React 19
- Deploy
- Single binary · Docker
Overview
Hlool PDF turns stamping contracts and invoices into a few drags. Seals, seam stamps and page edits are previewed live and exported as a new PDF, while the original file stays untouched.
The problem
Stamping PDFs usually means printing, stamping and scanning — or heavy desktop software. Seam seals that run across page edges are especially tedious, and uploading confidential contracts to unknown web tools is a non-starter.
How it works
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Local first: stamping, page organising, image conversion and AES-256 encryption run in the browser in a Web Worker, so files are not uploaded. The Go server is only a fallback and deletes its request-scoped temp files after each response.
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Direct manipulation: move, resize, rotate and fade seals with undo and redo; seam seals on any edge with real slice previews and seeded random slicing that matches between preview and output.
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Ships as a single Go executable with the React front end embedded, or as a Docker image for multi-user deployments with accounts, guest mode, rate limiting and S3-compatible storage.
What it does
Direct stamping
Drag, resize, rotate and fade seals on the page, with full undo and redo.
Seam seals
Cross-page seals on any edge, with 40 / 42 / 45 mm presets and live slice previews.
Batch workspace
Each file keeps its own setup; apply one setup to others and export in a queue.
Page organiser
Merge PDFs, reorder, rotate and delete pages, or turn images into pages.
Seal library
Import PNG, JPG or WebP seals with automatic white-background removal.
Encrypted output
Name files with templates and protect them with AES-256 encryption.
Inside the interface.
Project details
- Our role
- Designed, built and maintained as open source.
- Platforms
- Web · Windows · Docker
- Stack
- Go
- pdfcpu
- React 19
- TypeScript
- Tailwind CSS v4
- PDF.js
- qpdf-wasm
- SQLite
- S3 / R2
- Licence
- MIT
- First release
- 2026
Let's build the next Hlool PDF.
From first sketch to running in production — we build your product to the same standard as our own.