Calais is a service created by Thomson Reuters that automatically extracts semantic information from web pages in a format that can be used on the semantic web.^[1] Calais was launched in January 2008, and is free to use.^[2][3] The technology is now available via the website of Refinitiv, a provider of financial market data and infrastructure founded in 2018, that is a subsidiary of London Stock Exchange Group.^[4]

The Calais Web service reads unstructured text and returns Resource Description Framework formatted results identifying entities, facts and events within the text.^[5] The service appears to be based on technology acquired when Reuters purchased ClearForest in 2007.^[6]

The technology has also been used to automatically tag blog articles,^[7] and organize museum collections.^[8]

Calais uses natural language processing technologies delivered via a web service interface.