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Browser fingerprinting

Browser fingerprinting identifies a browser by combining many of its attributes into a near-unique signature. The attributes include headers, installed fonts, how the browser draws graphics and hardware signals. It works without cookies, so clearing cookies does not remove it. Sites use it to recognize returning visitors and to spot automated traffic.

Updated

How browser fingerprinting works

Scripts on a page read properties that the browser reports: its headers, screen size, time zone, fonts, the output of a hidden canvas and details about the hardware. Each value is common on its own. Together they can separate one browser from another. Because the signature is computed rather than stored on the device, deleting cookies does not remove it.

Why it matters for AI agents

Cloud and headless browsers can differ from a person's everyday browser in these attributes. Sites that use fingerprinting may flag such a browser, even when the request is harmless. That is one reason an agent running in a cloud browser can be blocked while the same task works in the user's own browser. The signal describes the browser, not the intent of the task.

Wield and browser fingerprinting

Wield recipes run in the user's everyday browser, through the Wield extension, with the session the user already has. Wield does not use a cloud browser for them. In our benchmark, as of 7 Nov 2026 (preliminary, still running), 10 sites blocked the automated cloud browser: bahn.de, Lieferando, Zalando, ImmoScout24, Idealo, Eventim, mobile.de, Walmart, Zillow and OpenTable. Wield does not promise that a site will never flag a run.

  • CAPTCHA: the visible check that a site may show when its other signals raise doubt.
  • Cloudflare Turnstile: a bot check that verifies visitors with light challenges.
  • Security model: what Wield stores and sends, and what it does not.

FAQ

This page does not give legal advice. Read the site's terms and the privacy rules that apply where you live. Fingerprinting is a technique that sites describe in their privacy policies, and those policies are the place to check how a particular site uses it.

Does incognito stop fingerprinting?

Private browsing mainly limits what the browser stores, such as cookies and history for that session. It does not change the browser attributes that fingerprinting reads. A private window therefore does not hide them.

Sources

  1. Fingerprinting (MDN)developer.mozilla.org