Build the fbc string

Summarize with:

A server Purchase matches the ad when user_data.fbc is the formatted ClickID. The fbclid in the URL is the last piece of that value.

Copy fbclid from the URL that still contains it. The redirect guide shows the hop that drops it, and formatting comes after that.

Click id Landing URL or fbclid

Paste the full address or the token alone, and the token keeps the casing you paste.

Domain index

Use 1 From the hostname Choose 0, 1, or 2

A server build with no saved _fbc cookie uses 1, which is the default here.

Click time

Now A time I enter

Now uses the millisecond clock at the moment you build the string, down to that instant.

Compare Existing _fbc, optional

Paste a cookie you already have, and the form only compares it with the string it builds.

The calculation stays in this browser, on the machine where you opened the form.

After you submit, the formatted string, the index, and the time show up here.

How the fbc parameter is set

Meta's parameter page says the formatted ClickID must be version, subdomainIndex, creationTime, and the fbclid, with a dot between each piece, and the version is always the letters fb.

subdomainIndex follows the cookie domain. In the examples on that page, com is 0, example.com is 1, and www.example.com is 2. A server build that never saved an _fbc cookie uses 1, so set the domain index to 1 in that case, and counting the hostname works the same way: one label is 0, two labels are 1, and three labels are 2. You pick the index yourself when a hostname has four or more labels, because those examples stop at a www host.

creationTime is the UNIX time in milliseconds when _fbc was stored, or when you first saw the fbclid if you do not save the cookie. When the browser did save _fbc, that cookie is already the formatted value, and the compare field checks a paste against a fresh build.

The fbclid segment preserves the casing Meta used in the URL, and changing that case breaks the match.

The string in Meta's example

fb.1.1554763741205.AbCdEfGhIjKlMnOpQrStUvWxYz1234567890

That is the value from the same documentation page: fb is the version and 1 is the domain index, while 1554763741205 is the creation time, and you should send all thirteen digits because the same moment in seconds would drop the last three. The last segment is the sample token, with its capitals kept as written.

Meta's parameter builder library documents this same order, before any optional appendix, and the form stops after the fbclid.

The field in the payload

The click id belongs in fbc. A payload that puts fbclid on its own inside user_data comes back with an unexpected-key error on that field.

After the string is ready

If a browser pixel also fires, both events need the same event id. The deduplication guide shows how to pair them. What each path sends is in the pixel and Conversions API guide.

When the sale arrives on a network postback, the offline guide covers the Meta upload. The postback URL builder assembles the network address, with the click id and the payout macro.

The late approval checker compares the click day with the day the sale becomes payable.

On Google, that click id is called gclid, and the tracking template builder places it on the URL a tracker reads.

My take

I would start by pasting the full URL, because that paste has both the token and the host, and I would judge the finished string by a thirteen-digit time and by capitals that still match the token. A raw fbclid field on user_data is what I would skip, since the click id already sits inside fbc.

When ElasticFunnels builds it

ElasticFunnels is a funnel platform for teams that run paid traffic. It builds the pages, split-tests variants under one URL, and hosts the checkout, with the click and the order on the same record.

On a hosted page, when there is no _fbc cookie, ElasticFunnels builds fbc from the fbclid in the landing URL. Its Meta Ads page says those checkout sales go to Meta as server-side Purchase events with fbc and fbp in the payload.

ElasticFunnels is newer than the platforms it competes with, and there is very little independent third-party review coverage to check that fbc build against. Until you run real volume through it, you are largely taking the vendor's word for the server Purchase. It has been on the market since 2023, which is why those outside write-ups are still thin. The pages, the same-URL test, and the checkout are part of the same account. The ElasticFunnels review goes through the rest of the platform.

Questions

How is fbc different from fbclid?

fbclid is the token Meta appends on the ad click. fbc is the server value, with the version, the domain index, and the time written in front of that token.

Which domain index should I use?

Use 1 when you format the click on the server and you never stored the cookie. Use 0 for a one-label cookie domain, and 2 when the cookie domain has a www label.

Should I send the raw fbclid?

Put the token inside fbc, because a payload that adds fbclid as its own user_data field fails validation.

Where does the creation time come from?

If a cookie was saved, the middle number is that save time in the long digit form from the example above, and if you never saved one, it is the time the token first arrived, in that same form.

What does the _fbc cookie hold?

The cookie is the formatted value, so paste one you already have into the compare field, and a match means the fresh build equals it, while a missing cookie means you build from the URL that still has the token.

Build the fbc string

How the fbc parameter is set

The string in Meta's example

The field in the payload

After the string is ready

My take

When ElasticFunnels builds it

Questions

Changelog

What we read

Related reading

Comments

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