What is Stealth Mode?

The best-known implementation is the stealth plugin for puppeteer-extra, a set of small evasions applied before any page script runs. Each repairs a single tell: navigator.webdriver removed, the plugin and mimeType arrays repopulated, window.chrome restored, notification permission state made consistent, WebGL vendor strings rewritten, iframe contentWindow behaviour corrected. Playwright users get comparable patches from separate packages. Injection goes through the DevTools protocol so the overrides are already in place by the time the page's own JavaScript starts looking.

Patching leaves residue of its own. An overridden native function whose toString() no longer prints [native code] is detectable in one line, so evasions proxy toString as well, and a careless proxy shows up in error stack traces instead. Enabling the CDP Runtime domain has historically been observable from inside the page. All of this moves: each published evasion becomes a signature a detection vendor can write a test for, and the popular open-source stacks are the most heavily studied code in the field.

JavaScript patches stop at the JavaScript boundary. The TLS handshake still produces the JA3 or JA4 fingerprint of whatever client performed it, the HTTP/2 SETTINGS frame and pseudo-header order still identify the engine, and the IP still carries its reputation and its ASN classification. A Node script that fakes Chrome's navigator object while handshaking like Node contradicts itself in a way no page-level evasion reaches. Driving a genuine Chrome build settles the transport half by construction.

Behaviour is the part teams skip. Human sessions have variable dwell time, mouse paths that curve and overshoot, scrolling that stops mid-page, typing with uneven gaps and the occasional correction. Automation without any of that produces near-identical intervals across thousands of requests, which clusters more easily than any single fingerprint value. Over-patching backfires as well, since a profile assembled from mutually impossible values - a Linux platform string beside a Windows font list - is rarer than the default it replaced.