zat

zat is a code outline viewer. It shows exported symbols and line numbers at a glance.

Works great as a tool for LLM coding agents — they can see the outline first, then Read only the parts they need.

The name comes from Japanese ざっと (zatto), meaning "roughly" or "at a glance".

Installation

Homebrew

brew install bglgwyng/tap/zat

Nix

Available in nixpkgs.

nix profile install nixpkgs#zat

Or run directly:

nix run nixpkgs#zat -- <FILE>

Also available via llm-agents.nix.

Home Manager

Add github:bglgwyng/zat as a flake input, import zat.homeManagerModules.default, and configure:

{
  programs.zat = {
    enable = true;
    claude-code.enable = true;
  };
}

Options:

• programs.zat.enable — installs the zat binary
• programs.zat.claude.enable — registers a zat rule under programs.claude-code.rules (requires a claude-code Home Manager module that exposes that option)

mise

mise use -g github:bglgwyng/zat

Or run directly:

mise x github:bglgwyng/zat -- zat <FILE>

Cargo

cargo install --git https://github.com/bglgwyng/zat

Pre-built binaries

Download from GitHub Releases. Available for macOS (aarch64, x86_64) and Linux (x86_64).

Usage

File outline

zat src/lib.rs

struct OutlineEntry { // L8-L12
  signature: String
  start_line: usize
  end_line: usize
}
struct ImportEntry { // L14-L18
  source_text: String
  start_line: usize
  end_line: usize
}
fn extract_outline(source: & str, path: & str) -> OutlineResult // L33-L196

Only public/exported symbols are shown. Visibility modifiers (pub, export) are stripped for brevity. Struct fields, enum variants, and interface members are included.

Supported Languages

Language	Extensions
JavaScript	.js, .jsx, .cjs, .mjs
TypeScript	.ts, .tsx, .mts, .cts
Rust	.rs
Python	.py
Go	.go
Java	.java
C	.c, .h
C++	.cpp, .cc, .cxx, .hpp, .hxx
C#	.cs
Swift	.swift
Kotlin	.kt, .kts
Haskell	.hs
Ruby	.rb

All languages are parsed with tree-sitter.

For AI Agents

Add this to your CLAUDE.md or AGENTS.md:

## Tools

### zat

A code outline viewer that shows exported symbol signatures with line numbers.

Prefer `zat` over `cat`/`Read` when you need signatures, not full implementation. Use the line numbers in the output to `Read(offset, limit)` into specific sections.

Supported languages: C, C++, C#, Go, Haskell, Java, JavaScript, Kotlin, Markdown, Python, Ruby, Rust, Swift, TypeScript/TSX

`zat` exits with code 1 for unsupported languages.