butter v2.1.0 — full parity with the reference compiler

Indentation-aware specs that compile themselves.

Butter is a minimalist, indentation-based specification language. Write a spec once, and the compiler turns it into precise AI agent prompts, JSON, or YAML — right in your browser.

Launch the IDE Browse examples

hello.butter

1# Hello World
2app HelloWorld
3  description "A simple demonstration"
4  version "1.0.0"
5
6feature Greet
7  description "Greets the user by name"
8  version "1.0.0"
9
10  params
11    name string
12
13  actions
14    "Say hello to the user"

Everything the cli tool does, in the browser

Compiler parity

The TS compiler is a byte-for-byte port of butter v2.1.0 — the same parser, semantic checks, formatter, and prompt / JSON / YAML output as the reference binary.

Butter Docs Colors

The exact syntax highlighting theme from the VS Code extension: keywords, strings, types, params and booleans color-coded for readability.

Live linting

Errors and warnings appear as you type, mirroring the extension's butter compile --check diagnostics with line ranges.

Intelligent completion

Context-aware suggestions for keywords, params, types, methods, returns and response schemas, ported straight from the extension's provider.

Hover & navigation

Hover a return payload to see its schema, or jump to a response declaration with Ctrl/Cmd+Enter or F12.

Format & compile

Shift+Alt+F applies the canonical formatter; compile to prompt, JSON or YAML with the same messages as the CLI.