What is content taxonomy?
A content taxonomy is a standard list of categories for describing what content is about, and in OpenRTB it usually means the IAB Tech Lab Content Taxonomy. Its codes fill fields such as Site.cat, App.cat, and Content.cat, and a matching cattax field says which taxonomy and version the codes come from, since codes differ between versions.
Also called: IAB content taxonomy, IAB categories, content categories, category taxonomy.
How it works
IAB Tech Lab has published several versions. Content Taxonomy 1.0 used codes such as IAB1 for Arts and Entertainment and IAB1-1 for one of its subcategories; version 2.0 and later replaced those codes with unique IDs per node and reorganized the tree. A separate Ad Product Taxonomy describes what an ad sells, and an Audience Taxonomy describes segments. The AdCOM Category Taxonomies list numbers them all: 1 and 2 are Content Category Taxonomy 1.0 and 2.0; 5, 6, 7, and 9 are Content Taxonomy 2.1, 2.2, 3.0, and 3.1; 3 and 8 are Ad Product Taxonomy 1.0 and 2.0; and 4 is Audience Taxonomy 1.1.
OpenRTB 2.6 added a cattax field next to each category array: Site.cattax, App.cattax, Publisher.cattax, Content.cattax, Producer.cattax, and Bid.cattax for the creative. BidRequest.cattax covers the bcat blocklist and the acat allowlist. Every one defaults to 1, so a payload that sends 3.x IDs without setting cattax tells buyers to read them as 1.0 codes. Genres follow the same pattern from 2.6-202505 on, with Content.genres and its own Content.gtax.
Pitfalls: mixing codes from two taxonomies in one array; sending IDs as integers instead of strings; and setting the request-level cattax for bcat while forgetting the content-level one. Content taxonomies describe pages, and the Ad Product Taxonomy was built to describe what an ad promotes, so confirm which one a partner expects for bcat and Bid.cat before moving off the 1.0 default.
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Related terms
Every term is in the glossary.