CoCounsel (Thomson Reuters)

CoCounsel is Thomson Reuters’ AI tool, integrated directly into Westlaw and Practical Law. It assists with legal research, document review, contract analysis, and memo drafting, with every answer backed by real case-law citations from the Westlaw database. This combination gives the user a sense that answers are grounded in real sources rather than just text generated by the model. The tool was built to match the language and workflow already familiar to lawyers using Thomson Reuters systems.

It’s a tool mainly aimed at litigation attorneys and corporate in-house counsel already subscribed to Westlaw, since it’s usually sold as an add-on or as part of an existing package rather than a standalone product with a public price. Its popularity is evident in its user numbers, with around a million users, making it the largest installed base among legal AI tools today. For a firm already paying for Westlaw, adding CoCounsel is usually seen as a natural upgrade rather than a separate purchase.

That said, it’s important to remember independent industry testing has found hallucination rates in legal AI tools remain a genuine concern, and that holds true even for tools built on authoritative case-law databases. It’s therefore recommended that every answer, even one backed by a citation, be manually checked before it’s sent to a client or submitted to a court. A lawyer not already a Westlaw customer will likely find that access to the tool first requires moving to Thomson Reuters’ broader system.