Authors WebdriverIO E2E tests - `npm init wdio@latest` scaffolding, services architecture (sauce, browserstack, appium, devtools), reporters (spec, allure, junit), built-in Mocha/Jasmine/Cucumber framework integrations. WebdriverIO sits between Selenium (W3C protocol) and Playwright (modern API) - Selenium-protocol-compatible with rich plugin ecosystem. Use when the team needs WebDriver protocol + service-based device-farm integration.