Web IDL is an interface description language (IDL) format for describing application programming interfaces (APIs) that are intended to be implemented in web browsers. Web IDL is an interface description language (IDL) format for describing application programming interfaces (APIs) that are intended to be implemented in web browsers. Web IDL is an IDL variant with: The first edition of the Web IDL specification became a Candidate Recommendation on 19 April 2012 and a W3C Recommendation on 15 December 2016. The second edition of Web IDL is an Editor's Draft, and most new web specifications reference this second edition.