All market data necessary for market resolution is available on-chain (ie ancillaryData in UMA 00 request), but Polymarket also provides a hosted service, Gamma, that indexes this data and provides additional market metadata (ie categorization, indexed volume, etc). This service is made available through a REST API. For public users, this resource read only and can be used to fetch useful information about markets for things like non-profit research projects, alternative trading interfaces, automated trading systems etc.

Endpoint

https://gamma-api.polymarket.com