Project rules file

A project rules file is a plain text file that sits alongside your code and tells an AI coding tool how your project works. It might say which language and frameworks to use, how to name things, which commands run the tests, and what the tool must never touch. The tool reads it automatically at the start of every session, so nobody has to paste the same instructions into each new chat. Claude Code and Cursor are examples of tools that offer this.

AI coding tools forget everything between sessions. Without a rules file, the same corrections get repeated every day, and different team members get different results from the same tool. A shared file keeps the output consistent and lets a new colleague get the same behaviour on day one. If you only use the tool for one-off scripts, you can skip it. If several people work on one codebase for months, it saves a lot of rework.

• Ask where the file lives and whether it is stored in the project, so it travels with the code and is shared by the whole team.
• Test it by adding one clear rule, such as a naming convention, and check that a fresh session follows it without being reminded.
• Find out whether rules can be set per folder or per user as well as per project.
• Check whether there is a size limit, since very long rule files can be partly ignored.