sig

Extract the public API surface from source files as compact JSON — function signatures, type/struct/interface definitions, const/var blocks — without implementation bodies.

Supported Languages

Extension	Language
.go	Go
.ts, .tsx, .mts, .cts	TypeScript
.cs	C#

Installation

go build -o sig
codesign -s - sig
sudo cp sig /usr/local/bin/
sudo codesign -f -s - /usr/local/bin/sig

Or with just:

just install

Usage

CLI

sig --cli file.go              # public API only
sig --cli --all file.go        # include private/unexported symbols

MCP Server

sig runs as an MCP JSON-RPC stdio server by default (no flags). Register it with Claude Code:

claude mcp add --transport stdio --scope user sig -- /usr/local/bin/sig

Tool: sig Parameters:

• file (string, required) — absolute path to source file
• all (boolean, optional) — include private/unexported symbols (default: false)

Output

Returns a FileShape JSON object:

{
  "file": "/path/to/file.go",
  "package": "main",
  "imports": ["fmt", "os"],
  "types": [
    {
      "name": "Server",
      "kind": "struct",
      "line": 15,
      "fields": [{"name": "Port", "type": "int"}],
      "methods": [{"name": "Start", "signature": "() error", "line": 20}]
    }
  ],
  "functions": [
    {"name": "NewServer", "signature": "(port int) *Server", "line": 10}
  ],
  "constants": [],
  "variables": []
}

License

MIT