Atdgen is a command-line program that takes as input type definitions in the ATD syntax and produces OCaml code suitable for data serialization and deserialization. Two data formats are currently supported, these are biniou and JSON. Atdgen-biniou and Atdgen-json will refer to Atdgen used in one context or the other. Atdgen was designed with efficiency and durability in mind. Software authors are encouraged to use Atdgen directly and to write tools that may reuse part of Atdgen’s source code.