Show HN: Zerostack, an open coding agent optimized for memory footprint

A new open-source coding agent called Zerostack, written in Rust, has been released with a memory footprint of approximately 16 MB average and 24 MB peak, compared to roughly 700 MB for JavaScript-based agents. The tool supports multiple AI providers, includes a terminal UI, permission system, and session management, and is available for installation via Cargo or pre-built binaries on GitHub.

Overview Minimal coding agent written in Rust — ~16k LoC, 26MB binary, ~16 MB RAM avg , ~24 MB peak . Peak RAM ~24 MB vs ~700 MB for JS-based agents. CPU: 0.0% idle, ~1.5% under load. Multi-provider — OpenRouter, OpenAI, Anthropic, Gemini, Ollama, plus custom providers Standard tools — all tools exposed to coding agents as described by opencode Permission system — 5 modes, per-tool patterns, session allowlists Terminal UI — crossterm, markdown rendering, mouse support, scrollback Prompts system — 10 built-in prompts, switchable at runtime Session management — save/load/resume, auto-compaction MCP support — connect external tool servers Ralph Wiggum loops — iterative coding for long-horizon tasks Git Worktrees — branch-per-task workflow ACP support gated — editor integration Zed, etc. Persistent memory gated — plain-Markdown memory across sessions Subagents — parallel, fast codebase exploration ARCHITECTURE.md — shared core knowledge for all agents on the same codebase Sandbox mode — bubblewrap / zerobox isolation Exa search — WebFetch & WebSearch tools zerostack-general room https://app.element.io/ /room/ zerostack-general:matrix.org on Matrix. Prompts Built-in system prompts that change the agent's behavior and tone — switch at runtime with /prompt : | Prompt | Description | |---|---| code | Coding mode with full file & bash access, TDD workflow | plan | Planning-only — explores and produces a plan without code | review | Code review for correctness, design, testing, and impact | debug | Finds root cause before proposing fixes | ask | Read-only mode — no writes or bash | brainstorm | Design-only — explores ideas without code | frontend-design | Distinctive, production-grade UI | review-security | Finds exploitable vulnerabilities | simplify | Refines for clarity without behavior change | write-prompt | Creates and optimizes agent prompts | Custom prompts can be created by placing markdown files in $XDG CONFIG HOME/zerostack/prompts/ . Permissions | Mode | CLI | Behavior | |---|---|---| restrictive | -R | Ask for every operation | readonly | --read-only | Read/grep/list only. Deny writes, edits, bash | guarded | --guarded | Allow reads. Ask for writes, edits, bash | standard | default | Allow path tools within CWD. Safe bash auto-allowed | yolo | --yolo | Allow everything, prompt for destructive commands | Per-tool granular glob patterns, session allowlists, and doom-loop detection prevent runaway agents. The --dangerously-skip-permissions flag bypasses all checks. Commands /model — Switch model /thinking — Set thinking level /clear — Clear conversation /session — List/save/load sessions /loop — Schedule recurring prompts /prompt — List or change system prompt /mode — Set permission mode /worktree — Create git worktree and move into it /wt-merge — Merge worktree branch, push, clean up, return /wt-exit — Return to main repo without merging /help — Show all commands 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 Installation Requires Cargo https://rustup.rs/ and git: Default — MCP, loop, git-worktree, and subagents cargo install zerostack With ACP Agent Communication Protocol support for editor integration cargo install zerostack --features acp With Memory support cargo install zerostack --features memory With experimental multi-threaded subagents cargo install zerostack --features multithread Pre-built binaries are also available on GitHub Releases https://github.com/gi-dellav/zerostack/releases . Once installed, run /prompt autoconfig inside zerostack to configure the tool interactively. Optional: Sandbox Debian/Ubuntu apt install bubblewrap Fedora dnf install bubblewrap Arch pacman -S bubblewrap Parallel Agent Run multiple zerostack agents on the same repository simultaneously without manual git worktree management. zerostack --parallel Each parallel agent operates in a temporary git worktree. Changes are merged and the worktree is removed when the agent exits. ACP Agent Communication Protocol With the acp feature, zerostack acts as an ACP Agent server, allowing editors like Zed to connect to it as a coding agent backend: Stdio mode editor spawns as subprocess zerostack --acp TCP mode zerostack --acp --acp-host 0.0.0.0 --acp-port 7243 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. Sessions 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.