What is ui.md?

UI.md is not a piece of software you install or run. It is a single text file containing a concise, opinionated set of design rules meant to be handed to a coding agent, such as Claude Code, before it starts writing user interface code. The idea is to give the agent a design contract to follow so it thinks about good UI behavior before it starts producing UI code, rather than just satisfying a feature checklist afterward. Using it is simple: you include the UI.md file in the coding agent's context when starting any task that involves building or changing a user interface, and you treat its contents as rules the agent should actually follow, not just a functional requirement to check off. At the end of the file there is a checklist you can use afterward to sanity check whatever UI the agent produced. The file itself is organized into a few sections. It opens with what it calls a prime directive, the idea that a UI is good when it behaves the way the user expected it to. From there it lists design priorities such as matching the user's mental model, focusing on the activities people are trying to complete rather than piling on features, reducing the number of decisions a user has to make, staying consistent, making actions obvious, and favoring recognition over making users recall things. It follows this with practical do and don't guidance, low level rules covering specific elements like buttons, forms, dropdowns, navigation, text, and error messages, and finally the usability review checklist mentioned above. The project is released under the MIT license, which is permissive and allows free reuse as long as the copyright notice is kept.