The agree grammar engineering environment is an open-source tool for developing—and parsing with—constraint-based grammars. Similar to the PET and LKB parsers and other tools used by DELPH-IN consortium researchers, agree processes computational grammars authored in TDL, a declarative type definition language based on the HPSG linguistic formalism.

The core type system, unification engine, lock-free parser, and console features of the system operate within the ECMA-335 Common Language Infrastructure (i.e., Mono and Microsoft .NET) on Linux and Mac, and Windows. In addition, there is a WPF graphical client application (which is only available on Windows).