fbc and fbp
Also called _fbc, _fbp, Meta browser cookies.
Two cookies the Meta pixel sets on your site. _fbc holds the click ID from a Meta ad, with the time it was seen; _fbp is an ID for the browser itself. Sent with a lead through the Conversions API, both help Meta match the lead to a person.
Why it matters
Meta matches mostly on hashed email and phone. When those are missing or do not match an account, these cookies are what is left, and they can only be read in the browser at the moment the form is filled. They cannot be rebuilt later from the CRM.
What goes wrong
_fbc only exists when the visitor arrived from a Meta ad with fbclid in the address and the pixel was on the page to read it. _fbp exists for any visitor the pixel has seen. Both have a fixed shape, fb.1. followed by a timestamp and an ID, and a value in any other shape is not one Meta will accept.
They go missing for the same reasons a click ID does: no hidden field to carry them, a form on another domain, or cookies blocked. Instant forms inside Facebook and Instagram never touch your site, so they carry Meta's lead ID instead.
How to check it on your own account
Open a recent website lead from Meta in your CRM and look for fields holding values that start with fb. followed by a number. If there are none, the cookies are not reaching the CRM.
Next to this
- fbclidMetaMeta's click identifier, appended to the landing page URL when someone arrives from a Facebook or Instagram ad.
- Conversions APIMetaMeta's server-to-server route for sending events, used alongside or instead of the browser pixel.
- Event Match QualityMetaMeta's score, from 1 to 10, for how well the customer information attached to your events lets Meta resolve them to a person.
- Hidden form fieldA field in a web form that the visitor never sees, filled in by the page itself.
How it applies in your trade
The same method, worked through for each kind of business: what a lead is worth, what is known on arrival and what to prepare.
The rest of this step
Measure this on your own data
The diagnostic reads a CRM export in your browser and reports your volume, your match rate and the spread between your leads against the thresholds in this glossary. Nothing is uploaded and no account is needed.