Definition
Deduplication is the process that prevents the same conversion from being counted multiple times when it's sent from both the browser (pixel) and the server (CAPI), typically by both sources sharing the same event_id.
Also called: Deduplication, Event dedup, Conversion dedupOne purchase. Consistent measurement.
- event_name
- Purchase
- event_id
- DEMO-1042
- Browser + server
- Same event, matched
01The purchase is recorded with a stable ID, value and currency.
Precision matters as much as coverage
Best practice is to run both pixel and server-side (CAPI), so you capture as many conversions as possible. But without deduplication, you then risk counting the same sales twice: once from the browser, once from the server. Double-counting poisons optimization just as much as gaps do: the algorithm learns from wrong numbers.
The solution is for both sources to send the same unique event_id, so the platform understands it's one event observed in two places — not two events. A good tracking setup is therefore as much about precision (dedup) as coverage (server-side). Both have to be in place for the signal to be clean.
Frequently asked questions
Why is deduplication necessary?
Because you should run both pixel and server-side for maximum coverage, but without dedup, the same conversions get counted twice. Double-counting gives the algorithm wrong data and hurts optimization as much as missing data does.
How does deduplication work technically?
By having both the pixel and the Conversions API send the same unique event_id for a given event. The platform recognizes the id and counts the event once, even though it came from two sources.
From insight to action
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About the author
Nicklas Segatz Mortensen
Growth hacker and fractional CMO with 10+ years' experience and hundreds of millions in managed ad spend behind him. Background from larger Danish and international scale-ups, and from the agency world.
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