FingerprintJS is a client-side browser fingerprinting library written in TypeScript. It collects over 30 entropy signals (canvas, audio, fonts, WebGL, etc.) from the browser environment and hashes them into a stable visitor identifier. The library operates in two phases: a load phase where entropy sources are prepared asynchronously, and a get phase where values are collected and combined. It includes stabilization logic for browsers that apply anti-fingerprinting measures (e.g., Safari 17, Firefox 120+) and provides a confidence score for the identifier. The architecture is modular: each entropy source is a separate function with a consistent interface, the agent orchestrates collection, and the hashing uses a custom MurmurHash3 x64 128-bit implementation. The library has no runtime dependencies and is tree-shakable. It is used for fraud detection and visitor identification without cookies.
This repository serves as a technical deep-dive into Google's reCAPTCHA system, particularly focusing on its obfuscation techniques, fingerprinting mechanisms, and anti-tampering measures. It includes extracted JavaScript snippets that implement specific browser fingerprinting signals (e.g., storage access checks, window opener properties, WebGL data extraction) and JSON files containing example fingerprint data. The repository also contains analysis of the now-removed BotGuard component, including its obfuscated virtual machine implementations. While the subject matter is largely historical due to the removal of BotGuard in April 2026, the repository provides valuable insights into the techniques used by advanced anti-bot systems.