Selenium
Selenium is a long-standing open-source project for automating web browsers, best known for Selenium WebDriver, which provides a common API for driving Chrome, Firefox, Safari, and Edge programmatically. It's one of the oldest and most widely deployed browser automation tools still in active use.
Selenium's core contribution was standardizing browser automation through the WebDriver protocol, which later became a formal W3C standard — meaning any browser vendor that implements WebDriver can be driven by the same Selenium-based test code, without tool-specific hacks per browser.
Compared to Playwright and Cypress, Selenium requires more manual handling of waits and synchronization (see explicit and implicit waits), which is a common source of flaky tests in older Selenium suites — but its maturity, huge ecosystem, and broad language support (Java, Python, C#, JavaScript, Ruby) keep it a dominant choice, especially in large, established organizations.
