About Koenji Lab
Koenji Lab is a collection of free, privacy-first developer tools that run entirely in your browser. Your data never leaves your device — no uploads, no server-side processing, no data collection, and no AI training.
Our Tools
- Cron Expression Builder — Build, validate, and visualize cron schedules
- JSON / YAML / TOML Converter — Convert between data formats instantly
- HEIC to JPG/PNG Converter — Convert iPhone photos without uploading
- Person Age Timeline — See what age famous people were when they created their works
Why “Koenji”?
Named after Koenji, a neighborhood in Tokyo known for its independent spirit, creative community, and DIY culture. That same ethos drives this project — building useful tools and sharing them freely.
Your Data Stays With You
Every tool on Koenji Lab processes data locally in your browser using JavaScript and WebAssembly. Your files and data never leave your device. We don't collect, store, or transmit anything you input. Your data is never used for AI training or sold to third parties.
Don't take our word for it — open your browser's Network tab and verify for yourself. Read our Privacy Policy for details.
Built With
Next.js, TypeScript, Tailwind CSS, and hosted on Cloudflare Pages. Data tools powered by open APIs from Wikipedia and Wikidata.