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zerostack

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

blogposts: what we built in 2 weeks memory design subagents design xavier's memory analysis

note: Want to support? Consider donating here; if you are a company interested in sponsoring zerostack, contact me here.

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: five configurable modes with per-tool patterns, session allowlists, and configurable mode-to-rule application 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.
• ACP support (gated): Agent Communication Protocol server — lets editors (Zed, etc.) connect to zerostack as an ACP agent
• Persistent memory (gated): plain-Markdown memory across sessions: a global MEMORY.md plus per-project daily logs, scratchpad, and notes, injected into the system prompt each session
• Lifecycle hooks (gated): observe or gate tool calls, prompts, and session lifecycle events via external commands, using a settings.json schema largely compatible with Claude Code hooks
• Advisor (gated): a second model the agent can consult mid-session for strategic guidance, with an optional human-handoff mode
• Multimodal input (gated): attach images and PDFs to messages
• Subagents: Parallel and fast, used for exploring the codebase
• ARCHITECTURE.md: Our own companion file for AGENTS.md, it allows to offer a shared core knowledge for all agents working on the same codebase
• Prompt chaining: offers to advance brainstorm → plan → code → review as each phase finishes, config-gated per transition
• Status signals: emits run-state events (start, stop, git-conflict, permission waits) over a Unix socket for external status bars or tooling (docs/STATUS_SIGNALS.md)

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.