# File formats¶

VerMoUTH introduces two new file formats. The .ff format for defining blocks, links and : ref:modifications <data:modification>. Note that you can also define blocks (and basic links) with Gromacs .itp and .rtp files. The .mapping format can be used to define mappings. Mappings that don’t cross residue boundaries can also be defined using .map files.

These file formats are still not finalized and subject to change. Therefore these file formats are not yet documented. If you need to implement (mappings for) your own residues you’ll need to reverse engineer the format from the existing files.

## .ff file format¶

Used for defining blocks, links and modifications.

## .mapping file format¶

Used for defining mappings for single blocks, modifications, and block mappings that cross residue boundaries.