Glossary
What is event deduplication?
Event deduplication is the process by which an ad platform recognizes that two reports (typically one from the browser pixel and one from a server) describe the same conversion, and counts it only once. On Meta, the browser and server copies are paired primarily by event name plus a shared event_id.
Sending the same conversion twice is deliberate redundancy. The pixel copy arrives when the browser allows it; the server copy arrives regardless. Where both get through, the platform discards one; where the pixel was blocked, the server event is the only copy and the conversion would otherwise have been lost.
For Meta’s Conversions API, deduplication keys on event_name and event_id: two events with the same pair, received within Meta’s deduplication window, are treated as one. The TikTok Events API uses an event_id in the same way, while Google Ads deduplicates purchase conversions primarily by order (transaction) ID.
Deduplication fails in predictable ways: if the pixel and the server generate different or random IDs for the same conversion, the platform counts it twice and your reported results inflate. The reliable pattern is a deterministic ID, derived from the order ID and shared by both copies at fire time.