Free
$0
Open-source coding agent under GPL-3.0. Install via cargo or pre-built binaries from GitHub Releases. No paid tiers.
Zerostack
A Unix-inspired, radically minimalistic coding agent written in pure Rust — ~16MB RAM, 12.9MB binary, 12k lines of code.
Zerostack is a Unix-inspired, radically minimalistic coding agent written in pure Rust — ~16MB RAM, 12.9MB binary, 12k lines of code. It supports OpenRouter, OpenAI, Anthropic, Gemini, and Ollama providers, includes a crossterm-based TUI, MCP support, an integrated loop system for long-horizon tasks, Git worktree integration, and an ACP (Agent Communication Protocol) server for editor integration.
+ Pros
- Radically lightweight (~16MB RAM vs 300-700MB for Claude Code/OpenCode)
- Pure Rust — no Node/Go/Python runtime dependency
- Integrated loop system for long-running autonomous tasks
- Git worktree integration for branch-per-task workflows
- ACP server enables Zed editor integration
- Multi-provider support including Ollama for local models
- 10+ built-in prompt modes (code, plan, review, debug, ask)
- Granular permission system with doom-loop detection
− Cons
- Very early stage (less than 2 weeks old, rapid API changes)
- Small community and plugin ecosystem
- TUI-only — no IDE plugin or web UI
- Documentation still maturing
- Windows support untested
- Loop and worktree features marked experimental
Pricing
Introduction
Zerostack is a Unix-inspired, radically minimalistic coding agent written in pure Rust. Its single purpose: be the lightest coding agent you can run — ~16MB RAM at idle, ~12.9MB on disk, CPU at 0.0% when doing nothing.
The coding agent landscape has grown bloated. Claude Code burns 300-700MB of RAM. OpenCode ships a full Node.js runtime. In a landscape of ever-growing resource demands, Zerostack went the other way: pure Rust, ~12k lines of code, a single statically-linked binary that runs on a Raspberry Pi 4.
Launched on GitHub on May 16, 2026, Zerostack hit nearly 1,000 stars within two weeks — a signal that the developer community has been waiting for a lightweight alternative.
At its core, it distills the coding agent to essentials: a crossterm-based TUI, a multi-provider LLM layer (OpenRouter, OpenAI, Anthropic, Gemini, Ollama), a session manager, and a permission system. Then it adds ambitious features — an integrated loop system for multi-step autonomous tasks, Git worktree integration for branch-per-task workflows, and an ACP server that opens the door to editor integration with tools like Zed.
Key Features
- Multi-Provider Support: Connect to OpenRouter, OpenAI, Anthropic, Google Gemini, Ollama, or any custom OpenAI/Anthropic-compatible endpoint. Provider configuration lives in a single JSON file.
- Tool Ecosystem: Read/write files, run shell commands, execute lua scripts, search with ripgrep, use semantic search (via Exa), and control the agent via tools. Tools are structured as a typed JSON function API — new tools can be added by dropping a Rust file into the tools directory.
- Monochrome Mode: Terminal-native TUI using crossterm, with a Monochrome mode available for minimal visual interference. Runs in any terminal emulator.
- Built-in Prompts: 10+ prompt modes (code, plan, review, debug, ask, brainstorm, and more) that template the system prompt and initial user message for common workflows.
- Permission System: Four permission modes (accept-all, accept-per-tool, per-tool-glob, ask-each), per-tool patterns, and doom-loop detection that halts tool calls when recursion is detected.
- Session Management: Persistent session history backed by a configurable data directory. Sessions resume across restarts. Each session tracks tool calls, token usage, and file modifications.
- Loop System (experimental): The loop system handles multi-step autonomous tasks by maintaining a plan, tracking completion, and iterating until done. Activate it with --loop, and Zerostack will plan, execute, validate, and refine until the task is complete — optionally creating a new Git branch for each task.
- Git Worktrees (experimental): Create isolated Git worktrees for each task, keeping your main working directory clean. This works for experiments, code reviews, and long-running feature branches without polluting the working tree.
Version History
Release v1.3.3
Release v1.3.2
Release v1.3.0
Initial public release
Signature Snippet
# Install via cargo
cargo install zerostack
# Launch
cd /my-project
zerostack
# Run with loop for long tasks
zerostack --loop
# Create a task in a separate branch
git worktree add -b feature/validate-api ../zt-validate-api
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