seleniumhq/selenium

Selenium is the most widely used open-source framework for automating web browsers. Its core purpose is to let developers write code that controls a browser the same way a human would, clicking buttons, filling in forms, navigating between pages, reading text from the screen, all without any manual interaction. This makes it invaluable for automated testing: you write a test once and can run it thousands of times against Chrome, Firefox, Safari, and Edge to verify your web application behaves correctly. At the heart of Selenium is WebDriver, a standardized protocol (formally defined by the W3C, the same body that defines HTML and CSS) that every major browser now implements natively. Your test code sends instructions to a WebDriver-compliant browser driver, which translates them into real browser actions. Because WebDriver is a web standard, the same test code works across different browsers without modification, just point it at a different driver. Selenium supports writing tests in multiple programming languages: Java, Python, JavaScript, Ruby, C#, and Kotlin all have official bindings. You pick your language, import the library, and write code like "open this URL," "find the button with this label," "click it," "wait for the page to load," "check the title matches." Beyond plain WebDriver, the project also includes Selenium Grid, which lets you run tests in parallel across many machines and browser configurations simultaneously, dramatically speeding up test suites for large applications. You would use Selenium when you need to test a web application automatically across browsers, scrape web content that requires JavaScript execution, or automate repetitive browser-based tasks. The framework is built primarily in Java for its core infrastructure, with the browser-specific drivers handled by each browser vendor. It is mature, widely supported, and the foundation that many higher-level testing tools are built on top of.