What it does
When a visitor arrives from a Meta ad, the URL carries an `fbclid` parameter. The pixel reads it and stores it in `_fbc` so a later conversion can be attributed to that click rather than merely to the browser.
It is worth noticing that the value exists in the URL before any script runs. A site that logs full URLs (in analytics, in server logs, in a support tool) is capturing the click identifier whether or not the pixel is allowed to.
What to write in a cookie declaration
Describe it as click-based advertising attribution and list Meta as the provider. It is a distinct purpose from `_fbp` and worth its own row.
| Field | Value |
|---|---|
| Name | _fbc |
| Provider | Meta |
| Purpose category | advertising |
| Consent category | Marketing |
| Expiry | 90 days (vendor default) |
| Storage | First-party, written by script |
Treat the expiry as indicative
The value above is the vendor’s documented default. Vendors change configuration and several browsers cap script-written lifetimes. Record what repeated scans observe on your own site, with the browser, region, path and interaction state; one run is not authoritative for every visitor.
Can a visitor refuse it?
Yes, in the marketing category. Note the caveat above: refusing the pixel stops the cookie, and does not stop the parameter appearing in your own logs.
A verification scan supplies runtime evidence for the pages and states it exercises. Test a fresh profile with no choice made, then after refusal, and reconcile observed storage with response headers, server-side integrations and paths the scan did not visit.
Common questions
What is fbclid?
A click identifier Meta appends to destination URLs so that a conversion can be tied to a specific ad click. It is the value that ends up in _fbc.
Sources and verification
Verified on . Product-behaviour statements were checked against the current implementation and tests. The links below are the verification basis recorded for this article. They support the stated facts, not a legal conclusion for every site or configuration; recheck changing vendor behaviour before relying on it in production.
- Meta for Developers: fbp and fbc parameters
Vendor documentation
Checked
- Meta: United States Regional Privacy Notice
Vendor documentation
Checked
See what your own site is loading
A browser scan reports the requests and storage it observed during the sampled journey. Use configured workspace scans to compare the states and pages that matter to your implementation.