How Tesseract.js Works in the Browser (Developer Guide)

An overview of how we compile Tesseract into WebAssembly to achieve lightning-fast OCR entirely on the client side.

WebAssembly Magic

Tesseract is a powerful C++ optical character recognition engine originally developed by HP and maintained by Google. Historically, you had to install it on a Linux server to use it in a web application.

Bringing C++ to the Browser

Thanks to WebAssembly (WASM), the entire Tesseract C++ codebase has been compiled into a format that modern web browsers (Chrome, Safari, Firefox) can execute at near-native speeds.

  • When you use Tuko's OCR tool, your browser downloads a `.wasm` binary file (around 2-3MB).
  • It also downloads a language data file (e.g., `eng.traineddata` for English).
  • Once loaded, the browser executes the OCR algorithms locally. This is why it works even if you disconnect from the internet, and why it is 100% private!

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