Yes, for hand sign detection mode. You can also use keyboard keys 1-9 as an alternative input method.

What technology does it use?

YOLOX-Nano for hand sign detection, ONNX Runtime WebAssembly for inference in the browser, and a T9 engine for predictive text input. No data leaves your device.

Yes, completely free and open source.

About Ketsuin

What is Ketsuin?

Ketsuin (結印) is a web-based input method that lets you type text using ninja hand signs detected through your webcam. Inspired by the hand seals from Japanese ninja tradition, it maps 12 zodiac seals to T9 phone keypad groups — enabling text input through gesture.

The name 結印 means "binding seal" in Japanese, referring to the hand positions used in ninja jutsu.

How It Works

Allow webcam access when prompted
Form one of the 12 ninja hand seals in front of your camera
The AI model (YOLOX-Nano) detects your hand sign in real time
Each sign maps to a T9 key group (like an old phone keypad)
Combine signs to spell words — cycle through candidates with the Boar seal

Technology

YOLOX-Nano — lightweight object detection model for hand sign recognition
ONNX Runtime Web — runs ML inference entirely in the browser via WebAssembly
T9 Engine — predictive text input mapped to 12 ninja seals
React 19 + TypeScript + Vite — modern web stack
Cloudflare Workers + D1 — global leaderboard for challenge mode

All detection happens locally in your browser. No video data is sent to any server.

Challenge Mode

Test your hand sign speed by performing jutsu sequences as fast as possible. Compete on the global leaderboard and earn ninja ranks from Genin (rookie) to Six Paths (godlike speed).

There are 8 jutsu challenges ranging from Chidori (4 seals, difficulty 1) to the legendary Water Dragon (44 seals, difficulty 5).

Open Source

Ketsuin is free and open source. Source code: github.com/huanglizhuo/Ketsuin. See also the 12 hand signs reference.