VS Code Extension

Syntax highlighting, auto-formatting, linting, and code completion for .butter files.

IntelliSense — Context-aware autocomplete for keywords, types, and block-level suggestions.
Syntax highlighting — Full TextMate grammar with named captures for all Butter keywords.
On-save formatting — Runs butter fmt automatically on every save.
On-save linting — Validates syntax with butter compile --check, shows errors as red squiggles.
Auto-indentation — Smart indent for feature, endpoint, params, actions, responses, returns, and rules blocks.
Comment toggle — Ctrl+/ toggles # line comments.
Document icon — Custom SVG icon for .butter files.

Installation

# Via install script
./install.sh extension

# Manually
code --install-extension butter-extension.vsix

# Or open butter-extension/ in VS Code and press F5

Settings

Setting	Default	Description
`butter.compilerPath`	`"butter"`	Path to the `butter` binary. Change this if the binary isn't on your PATH.
`butter.compileOnSave`	`false`	Compile the spec on save and write generated outputs next to the source file.
`butter.compileFormats`	`["prompt"]`	Output formats generated on save when `butter.compileOnSave` is enabled. Supported: `prompt`, `json`, `yaml`.

Output Extensions

Butter's output formats are pluggable. Built-in formats:

Name	Extension	Use case
`prompt`	`.prompt.md`	Default. Markdown spec for pasting into AI chat.
`json`	`.json`	Structured data for AI agents and programs.
`yaml`	`.yaml`	Human-readable config and documentation.

Select with --format / -f. Prompt is the default.

Writing Output Extensions

Adding a new output format is a single Go file. Implement three methods:

package toml

import (
    "butter/pkg/ast"
    "butter/pkg/output"
)

func init() { output.Register(tomlExt{}) }

type tomlExt struct{}

func (tomlExt) Name() string          { return "toml" }
func (tomlExt) FileExtension() string { return ".toml" }
func (tomlExt) Serialize(spec *ast.AppSpec) ([]byte, error) {
    // your serialization logic
}

Then add a blank import to cmd/root.go and rebuild. The extension appears in --format help automatically.

The Serialize method receives a validated *ast.AppSpec with full access to spec.App, spec.Features, spec.Endpoints, params, actions, responses, returns, and enforce rules.