claude-agent-rs

A 2.8MB Rust binary that runs Claude as a full coding agent on your Max subscription. Zero API costs.

Live Site · crates.io · Test Results

What is this?

An 11-layer AI coding agent written in Rust. It has a REPL, 7 built-in tools, MCP server integration, skill dispatch, hooks, permissions, and memory — all wired to call Claude via claude -p so it uses your Max subscription instead of API credits.

$ ./claude-agent
  claude-agent v0.1.0 (Rust)
  claude-opus-4-6 · effort: High · backend: cli (Claude Max)
  7 tools · 11 MCP servers · 11 skills · 5 hooks

❯ write a fizzbuzz in Rust, compile it, run it
  ▸ write: /tmp/fizzbuzz.rs
  ✓ File written
  ▸ bash: rustc /tmp/fizzbuzz.rs -o /tmp/fizzbuzz && /tmp/fizzbuzz
  ✓ 1, 2, Fizz, 4, Buzz...

Architecture

Layer	Name	File	Purpose
1	Crown	`skills.rs`	Skill registry + /command dispatch
2	Skull	`hooks.rs`	Lifecycle hooks (pre/post tool use)
3	Security Cage	`permissions.rs`	Permission-gated tool access
4	Brain Core	`inference.rs`	Dual-backend inference (CLI + API)
5	Frontal Lobe	`context.rs`	Context engine + CLAUDE.md injection
6	Temporal Lobe	(stubs)	Agent spawner (future)
7	Auth Gate	`auth.rs`	Authentication routing
8	Brainstem	`tools/`	7 built-in tools
9	Root System	`mcp/`	MCP server discovery + registry
10	Pedestal	`inference.rs`	HTTP client (reqwest)
11	Workbench	`flags.rs`, `telemetry.rs`	Feature flags + session metrics

Built-in Tools

bash — Execute shell commands with timeout and error handling
read — Read file contents with line numbers
write — Create or overwrite files
edit — Exact string replacement in files
glob — Pattern-based file search
grep — Regex content search (ripgrep-style)
web_fetch — HTTP GET requests

Two Inference Backends

CLI Mode (default) — $0/month

Pipes prompts to claude -p --output-format json, which uses your Claude Max subscription's OAuth token. No per-token billing.

API Mode — pay-per-token

Direct POST to api.anthropic.com/v1/messages. Requires ANTHROPIC_API_KEY. Used when no CLI is available or for CI/CD.

Install

git clone https://github.com/ExpertVagabond/claude-agent-rs.git

cd claude-agent-rs

cargo build --release

./target/release/claude-agent

Requires:

Rust 2021 edition
claude CLI installed (for CLI backend)
Claude Max subscription (for $0 inference)

Test Results

28/28 tests passing against Claude Opus 4.6 on Max subscription:

Simple math, bash, read, write, edit, glob, grep, web_fetch
Multi-step tool chains (3-4 tools in sequence)
Error handling (missing files, zero matches, non-zero exit codes)
Security (refused rm -rf /)
Unicode/emoji preservation
Large stdout handling (500+ lines)
Skill dispatch, built-in commands
Write + compile + run Rust code

Full results: gist

Stats

Binary: 2.8MB (release, LTO, stripped)
Source: 3,454 lines across 21 files
Dependencies: 13 crates
Startup: <100ms
Response time: 11-160s per turn (depends on task complexity)

License

MIT

claude-agent-rs 0.4.0