Use open standards 
Requirements
For features of a codebase that facilitate the exchange of data the codebase MUST use an open standard that meets the Open Source Initiative Open Standard Requirements.
Any non-open standards used MUST be recorded clearly as such in the documentation.
Any standard chosen for use within the codebase MUST be listed in the documentation with a link to where it is available.
Besides making a list, consider adding badges to the repository for the standards used so that contributors immediately see shat is required for a contribution to the codebase.
Examples
- Standard for Public Code - showing both a badge in use and instructions for how to apply it.