A GUSTO.md file is a brand's verbal identity, written as a single document an AI agent can read. It describes how the brand sounds — its vocabulary, sentence rhythm, tonal modes, cultural references, and refusals. The file pairs with a DESIGN.md file the same way a copy deck pairs with a style guide.
The visual layer of brand identity has a working machine-readable standard. The verbal layer did not. GUSTO.md is the verbal layer.
How to use one
Drop a GUSTO.md into the root of your project. Reference it in your agent's system prompt or memory file. The YAML tokens act as rules. The markdown body sets the voice. The same file works across Claude, ChatGPT, Cursor, and any agent that can read markdown.
The exemplars on this site — Apple, Liquid Death, and the brands that follow — are reference implementations. Try one on the home page to read this site in that voice. Open the brand page to view the full file and download it for your own project.
Status
The specification is at version 0.1.2, under active development. Breaking changes are possible before 1.0. The exemplars are MIT-licensed; the specification is Apache-2.0.
Read the spec for the normative reference, or browse the exemplars from the home page.