zerostack

zerostack is a lightweight, open-source AI coding agent built in Rust by Giuseppe Della Vedova, designed to run entirely in the terminal with a minimal resource footprint. It is licensed under GPL-3.0 and installable via Cargo, Homebrew, Nix, or a curl script. The project is actively maintained, with its latest release (v1.8.4) published in September 2026.

What It Is

zerostack is a terminal-based coding agent that connects to multiple LLM providers and exposes a rich set of tools for reading, writing, editing, and executing code — all from a crossterm-based TUI with markdown rendering and mouse support. It is inspired by pi and opencode, and positions itself as a performance-conscious alternative to JavaScript-based coding agents. The README states a RAM footprint of approximately 16 MB on average (with peaks around 24 MB), compared to approximately 300 MB for opencode, and a binary size of 26 MB.

Architecture and Performance Profile

zerostack is written entirely in Rust, which the project credits for its low memory and CPU overhead. Key performance figures published in the README:

• ~30,000 lines of code (core, excluding tests)
• 26 MB binary size
• ~16 MB average RAM, ~24 MB peak
• 0.0% CPU at idle, ~1.5% when using tools (measured on an Intel i5 7th gen)

The agent runs as a single CLI binary and communicates with LLM providers over HTTP. It emits run-state events over a Unix domain socket (--status-socket) for integration with external status bars or tooling.

Permission System and Sandbox

One of zerostack's distinguishing design choices is its five-tier permission system:

• restrictive — asks for every operation
• readonly — allows only read/grep/list; denies writes, edits, and bash
• guarded — allows reads, asks for writes and bash
• standard (default) — allows path tools within the current working directory; safe bash commands auto-allowed
• yolo — allows everything, prompts only for destructive commands

Per-tool glob patterns, session allowlists, and doom-loop detection (identical tool calls repeated 3+ times trigger a warning or denial) are built in. An optional sandbox mode uses bubblewrap (Linux) or zerobox (macOS) to isolate bash commands, masking credential directories like ~/.ssh and ~/.aws by default.

Feature Set and Gated Capabilities

The default build includes multi-provider support (OpenRouter, OpenAI, Anthropic, Gemini, Ollama, and custom providers), MCP server integration, session save/load/resume with auto-compaction, 14 built-in switchable system prompts, Git worktree integration, parallel subagents, iterative coding loops, Exa web search, and prompt chaining (brainstorm → plan → code → review). Several advanced features are compile-time gated and require explicit feature flags:

• memory — plain-Markdown persistent memory across sessions
• hooks — lifecycle hooks compatible with Claude Code's settings.json schema
• advisor — a second model consulted mid-session for strategic guidance
• acp — Agent Communication Protocol server for editor integration (e.g., Zed)
• multimodal / pdf — image and PDF attachment support

Update: v1.8.4

The GitHub metadata shows the latest release is v1.8.4, published on 2026-09-07, with the repository last updated on 2026-09-14. The project has accumulated over 1,600 stars and 135 forks since its creation in May 2026. The developer has published blog posts covering the memory design, subagent architecture, and a "what we built in 2 weeks" retrospective, signaling rapid early development. A companion tool, multistack, is available separately for orchestrating multiple zerostack agents in parallel from the terminal.