- Course overview
- Search within this course
- What can I do with OLS?
- Free Text Search
- Searching ontologies in OLS
- Exploring Ontologies in OLS
- Exploring Entities in OLS
- OLS API
- Your feedback
- Get help and support on OLS
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What is Ontology Lookup Service (OLS)?
The Ontology Lookup Service (OLS) is a free, publicly available repository for biomedical ontologies that provides a single point of access to the latest ontology versions. Users can browse ontologies through the website as well as programmatically via the OLS API (see figure below).
OLS currently indexes around 277 ontologies comprising more than 9 million classes. As of 2025, OLS on average handles 30-40 million (both web and API) requests per month.
The Ontology Lookup Service is developed and maintained by the Samples, Phenotypes and Ontologies Team (SPOT) at EMBL-EBI.