TandaAir
A privacy-first watermarking studio for images and PDFs. Everything runs in your browser, nothing is ever uploaded.
- Client
- Personal product
- Role
- Creator & Developer
- Timeline
- 2025–2026
- Year
- 2026
Overview
A watermarking tool that treats privacy as the feature. You can batch-watermark images and PDFs, tune every parameter, and export, and not a single byte of your files ever leaves the device. It installs as a PWA and works offline.
The problem
Most online watermarking tools upload your documents to a server you have to trust. For IDs, contracts, and personal photos, that trade is unacceptable.
Goals
- Never transmit user files, process entirely on-device.
- Handle both images and multi-page PDFs.
- Stay responsive on large batches.
- Work offline, installable like an app.
Privacy-first architecture
There is no backend for files. Images are composited on a canvas; PDFs are parsed with PDF.js and rewritten with pdf-lib. Heavy work is offloaded to Web Workers so the UI never blocks, and Zustand holds a predictable state tree. Because processing is local, the app ships as an offline-capable PWA.
What it does
Batch watermarking
Drop in many files; apply one watermark configuration across all of them.
Image + PDF engines
Canvas compositing for images; PDF.js + pdf-lib for true multi-page PDFs.
Web Worker offloading
Rendering runs off the main thread, so the interface stays smooth on big jobs.
Installable & offline
A PWA you can install and use with no connection at all.
Why it matters
TandaAir proves a privacy claim you can verify: turn off your network and it still works. It's a small product with an opinion, your files are yours.
Lessons
Pushing real work to the client changes the engineering: memory, worker messaging, and file APIs become the design. The constraint, never upload, made the product clearer, not weaker.