zerostack

Minimal coding agent written in Rust, inspired by pi and opencode.

Features

• Multi-provider: OpenRouter, OpenAI, Anthropic, Gemini, Ollama, plus custom providers
• Standard tools: all of the standard tools exposed to coding agents, as described by the opencode documentation.
• Permission system: four configurable modes with per-tool patterns, session allowlists, and external directory policies
• Session management: save/load/resume sessions, auto-compaction to stay within context windows
• Terminal UI: crossterm-based, markdown rendering, mouse selection/copy, scrollback, reasoning visibility toggle
• Prompts system: switch between system prompt modes at runtime (code, plan, review, debug, etc.) to tailor the agent's behavior to the task without having to manage Skills.
• MCP support: connect MCP servers for extended tooling (exposed as an optional compile-time feature)
• Integrated Exa search: allows for WebFetch and WebSearch tools
• Integrated Ralph Wiggum loops: looping capabilities for long-horizon tasks
• Integrated Git Worktrees integration: Use /worktree to move the agent from one worktree to another.

NOTE: Windows support is not tested is any way, but feel free to try and open an issue if you encounter any bugs!

Performance

zerostack is one of the smallest and most performant coding agents on the market.

• Lines of code: ~7k LoC
• Binary size: 8.9MB
• RAM footprint: ~8MB on an empty session, ~12MB when working (vs ~300MB for opencode or other JS-based coding agents)
• CPU usage: 0.0% on idle, ~1.5% when using tools (measured on an Intel i5 7th gen, vs ~2% on idle and ~20% when working for opencode)

Installation

In order to install zerostack, you must have Cargo and git installed. Then, run:

cargo install zerostack

You are now ready to work with a lightweight coding agent! (Note: you can also find pre-built binaries on Github Releases)

Optional: sandbox mode

Install bubblewrap for --sandbox, which runs every bash command inside an isolated environment to protect your system from accidental or malicious damage:

# Debian/Ubuntu
apt install bubblewrap

# Fedora
dnf install bubblewrap

# Arch
pacman -S bubblewrap

Quick start

# Set your API key (OpenRouter is default)
export OPENROUTER_API_KEY="[api_key]"

# Interactive session (default prompt: code)
zerostack

# Monochrome TUI
zerostack --no-color

# One-shot mode
zerostack -p "Explain this project"

# Continue last session
zerostack -c

# Explicit provider/model
zerostack --provider openrouter --model deepseek/deepseek-v4-flash

Configuration

See CONFIG.md for config file location, accepted keys, provider aliases, permission rules, and MCP server configuration.

Prompts system

zerostack includes a set of built-in system prompts that change the agent's behavior and tone.
The idea is to build a complete suite of prompts that can fully substitute skills like superpower or the Claude's official skills.
You can switch between different prompts or list all registered prompts using /prompt.

Built-in prompts:

You can also create custom prompts by placing markdown files in $XDG_CONFIG_HOME/zerostack/prompts/ and referencing them by name.

Additionally, the agent automatically loads AGENTS.md or CLAUDE.md from the project root or any ancestor directory, injecting their contents into the system prompt. Use -n / --no-context-files to disable this.

Permission system

zerostack has four permission modes, from safest to most permissive:

1. restrictive (-R): every tool action prompts for approval unless explicitly allowed in config
2. standard (default): safe commands (ls, cd, git log, cargo check) are auto-approved; writes and destructive operations ask
3. accept-all (--accept-all): auto-approves all operations inside the working directory; external paths prompt for confirmation
4. yolo (--yolo): auto-approves everything without prompting

Permissions can be configured per-tool with granular glob patterns in the config file. For example, you can allow write **.rs automatically while always asking before writing to other files.

A session allowlist persists approved decisions for the duration of the session, so you don't have to repeatedly confirm the same operation.

Doom-loop detection: identical tool calls repeated 3+ times trigger a warning prompt (or denial depending on your config), preventing runaway agents from spamming destructive operations.

Slash commands

This is a list of the most important slash commands:

• /model — Switch model
• /thinking — Set thinking level
• /clear — Clear conversation
• /session — List/save/load sessions
• /loop — Schedule recurring prompts
• /prompt — List or change the agent's prompt
• /mode — Set the permission system's mode

To see all of the commands, use /help.

Session management

Sessions are saved to $XDG_DATA_HOME/zerostack/sessions/. Use -c to resume the most recent session, -r to browse and select one, or --session <id> to load a specific session.

Loop system

zerostack includes an iterative coding loop for long-horizon tasks. The agent repeatedly reads the task, picks an item from the plan, works on it, runs tests, updates the plan, and loops until the task is complete or the iteration limit is reached.

NOTE The loop system is an experimental feature.

Loop usage

/loop Implement the user authentication system
/loop stop
/loop status

• /loop <prompt> — Start a loop with the given prompt
• /loop stop — Stop the active loop
• /loop status — Show current loop state

Each iteration includes the original task, the evolving LOOP_PLAN.md, a summary of the previous iteration, and any validation output. Non-slash input is blocked while a loop is active.

Headless loops via CLI

zerostack --loop --loop-prompt "Refactor the API" --loop-max 10 --loop-run "cargo test"

Git worktrees integration

zerostack provides a branch-per-task workflow using git worktrees. You can create, work in, merge, and exit worktrees entirely from the chat UI.

NOTE The git worktrees integration is an experimental feature.

Git worktree usage

The worktrees integrations offers 3 slash commands:

Example workflow for git worktrees

1. Create — /worktree feature-x creates a new branch and worktree directory and moves you there.
2. Work — Use zerostack normally; changes stay on the feature branch.
3. Merge — /wt-merge tells the agent to merge the branch, push, clean up, and return to the main repo.
4. Exit — /wt-exit immediately returns to the main repo without merging.

Supported providers

• OpenRouter (default)
• OpenAI-compatible (vLLM, LiteLLM, etc.)
• Anthropic
• Gemini
• Ollama

Custom providers can be configured with any base URL and API key environment variable in $XDG_CONFIG_HOME/zerostack/config.json.

License

GPL-3.0-only