Identifier atlas
A tracking identifier may arrive in a URL, be retained in a cookie, and then be forwarded in a request or server payload. This atlas separates each surface for Google, Meta, and TikTok.
An identifier being present at one step does not prove it exists at the next. Each transition must be checked separately.
The click ID arrives as a URL parameter.
A tag may derive or retain a value in the browser.
The browser forwards permitted fields to a destination.
A server layer maps available values to the API.
Diagnostics become confusing when a name such as ttclid, fbc, or _ttp is treated as a simple “cookie.” One journey may contain a URL parameter, a first-party cookie, and an API field that are related but technically distinct.
This atlas shows where each artifact exists, how it may move to the next surface, and where to inspect the chain when attribution disappears.
Confusing a URL parameter with a cookie that has the same name.
4 documented families
Browser identity
The _ga cookie helps Google Analytics distinguish browsers. Its name and duration can be configured.
_gaGA4 client cookie
Sources
Each fact above cites its own evidence. Archived sources remain visible but support only qualified or conditional statements.
A tracking identifier may arrive in a URL, be retained in a cookie, and then be forwarded in a request or server payload. This atlas separates each surface for Google, Meta, and TikTok.
Analytics storage reads and writes depend in part on the analytics_storage signal in Consent Mode.
Google documents a first-party cookie managed by the GA client in the server container. The current documentation does not name this cookie FPID, so that name remains an advanced topic requiring revalidation.
Verified on 2026-08-27 · Review after 2026-10-27
Session
GA4 uses a stream-specific cookie to retain session information.
_ga_<container-id>GA4 session cookie
^_ga_[A-Z0-9]+$Verified on 2026-08-24 · Review after 2026-11-24
Click identity
gclid, gbraid, and wbraid arrive in the URL. Google tags may then retain advertising information in _gcl_* cookies and in _gcl_ls.
gclidGCLID click parameter
gbraidGBRAID parameter
wbraidWBRAID parameter
_gcl_*Google conversion cookie family
^_gcl_.+$_gcl_lsConversion Linker local storage
_gcl_auAdvertising measurement cookie
In Consent Mode, ad_storage controls access to advertising storage, but this Google signal does not replace legal consent analysis.
Verified on 2026-08-27 · Review after 2026-10-27
Cross-domain linker
The _gl parameter temporarily transports encoded measurement values between configured domains.
_ga / _gcl_*Source measurement values
_glLinker parameter
_ga / _gcl_*Destination measurement values
_glDecodeSymptomThe _gl parameter disappears before the destination page.
CheckInspect redirects, link decoration, the domain list, and the delay between generation and reading.
Verified on 2026-08-24 · Review after 2026-11-24
2 documented families
Click identity
fbclid arrives in the URL. A formatted value may be stored in _fbc and then sent to the Conversions API in the fbc field.
fbclidMeta click parameter
_fbcMeta click cookie
fbcConversions API fbc field
The Meta server tag template documents a cookie extension option with a 90-day default. This is not a universal _fbc lifetime.
Verified on 2026-08-24 · Review after 2026-11-24
Browser identity
The _fbp cookie and server-side fbp field are two distinct surfaces in the same functional family.
4 documented families
Click identity
ttclid may arrive in the URL, be retained in a first-party cookie with the same name, and be forwarded with events.
ttclidTikTok click parameter
ttclidTikTok click cookie
user.ttclidEvent Click ID field
Verified on 2026-08-27 · Review after 2026-10-27
Browser identity
TikTok documents _ttp as both a first-party and third-party cookie. The first-party value can populate user.ttp in the Events API 2.0.
_ttpFirst-party _ttp cookie
Session
TikTok documents generic and pixel-specific session cookies.
ttcsidTikTok session cookie
Browser identity
The _pangle cookie is a conditional third-party artifact related to use of the Pangle network.
_panglePangle cookie
G04Tier 1GBRAID and WBRAID parameters
Verified on 2026-08-24
Consent Mode and server-side tracking are complementary. The first orchestrates what may fire based on consent; the second improves technical control over data flows. Neither replaces strong governance.
_ga / _gcl_*Read values on the destination domain.
fbcForward the stored value in the server-side fbc field.
fbpConversions API fbp field
Verified on 2026-08-24 · Review after 2026-11-24
user.ttclidForward the Click ID with eligible events.
_ttpThird-party _ttp cookie
user.ttpTikTok Events API cookie field
Blocking the third-party cookie does not necessarily imply absence of the same-named first-party cookie, and vice versa.
SymptomTwo _ttp cookies appear to behave inconsistently.
CheckCompare their domain, first-party or third-party context, and attributes before drawing a conclusion.
Verified on 2026-08-27 · Review after 2026-10-27
ttcsid_<pixel-code>Pixel-specific session cookie
^ttcsid_.+$SymptomThe expected ttcsid_<pixel-code> cookie is absent.
CheckCheck the loaded Pixel code, consent, and whether the Pixel actually fired.
Verified on 2026-08-24 · Review after 2026-11-24
SymptomThe _pangle cookie is absent.
CheckFirst confirm that Pangle is part of the tested configuration; its absence may be expected.
Verified on 2026-08-24 · Review after 2026-11-24