Koenji Lab
Free developer tools. Your data never leaves your browser.
No signup. No data collection. No AI training. Everything runs locally in your browser.
Cron Expression Builder
Build, validate, and visualize cron schedules. Runs entirely in your browser.
JSON / YAML / TOML Converter
Convert between JSON, YAML, and TOML locally. Nothing is sent to any server.
HEIC to JPG Converter
Convert iPhone HEIC photos to JPG/PNG. Processed locally via WebAssembly — your photos never leave your device.
Person Age Timeline
See what age famous people were when they created their works.