Stealth mode refers to a collection of patches and overrides applied to a headless browser automation framework to make it indistinguishable from a real user's browser. Without stealth patches, headless Chromium exposes numerous signals that anti-bot systems use to identify automation: `navigator.webdriver = true`, absent Plugin arrays, empty `window.chrome` runtime, distinctive Canvas rendering, and anomalous timing signatures.
A complete stealth implementation patches: the `webdriver` property to be undefined rather than `true`, the Chrome runtime object (`window.chrome`, `window.cdc_*`), the Plugins array with plausible plugin entries, language and platform properties to match the claimed user agent, Canvas and WebGL rendering to add controlled noise, and timing functions to eliminate automation-induced precision patterns.
Open-source libraries like `playwright-stealth` and `puppeteer-extra-plugin-stealth` provide these patches as modular add-ons. AlterLab's Tier 3 applies a comprehensive stealth patch set to Playwright, with fingerprint profiles that are regularly updated to match current Chrome stable release characteristics across the most common OS/GPU combinations.