mcp-crewd-rs

mcp-crewd-rs

crewd is a cell fabric daemon for AI agents: it lets one AI session (Claude Code, Codex CLI, or any MCP client) spawn, coordinate and message other AI worker sessions — *cells* — through a single MCP server. Rust, one static binary per component, no network listener: everything runs over a local Unix socket.

Part of the mcp-*-rs family of Rust MCP servers.

┌────────────┐  MCP stdio   ┌──────┐   UDS (NDJSON)   ┌───────┐  spawns   ┌─────────────────┐

│ Claude Code│─────────────▶│ crew │─────────────────▶│ crewd │──────────▶│ engine processes│ │ / Codex CLI│ cell_* tools│ shim │ 0600 socket │daemon │ │ claude / codex │ └────────────┘ └──────┘ └───────┘ │ / pi workers │ └─────────────────┘

Components

MCP tools

Mounted per-cell via crew mcp:

• Fabric — cell_spawn (launch a worker cell: engine + profile + task), cell_send_task, cell_status, cell_result, cell_cancel, cell_list
• Bus — cell_send (fire-and-forget), cell_ask / cell_await (ask ticket + long-poll reply), cell_reply, cell_broadcast, cell_inbox

Worker cells get the same shim with --worker-mode, which hides the spawn surface (no uncontrolled nested fan-out).

Engines

Claude profiles select where the engine gets its credentials. max (the default) uses the host's own Claude credentials and needs no extra config. Additional profiles route the engine to an Anthropic-compatible endpoint, reading that profile's bearer token from keys_env_path (never from crewd.toml, argv or logs); the built-in ones are defined in the engine-claude adapter.

A cell's identity is its working directory: the spawned engine loads whatever CLAUDE.md, .mcp.json, memory and skills live in the cwd you pass to cell_spawn. One daemon can therefore serve several "personas" by spawning cells in different project roots.

Install

Prebuilt binaries (recommended) — download the archive for your platform from the latest release and extract; it contains crewd, crew and the shim/ directory:

tar xzf mcp-crewd-rs-x86_64-unknown-linux-gnu.tar.gz

install -m755 mcp-crewd-rs-*/crewd mcp-crewd-rs-*/crew ~/.local/bin/

Prebuilt targets (Linux + Android): x86_64-unknown-linux-gnu, x86_64-unknown-linux-musl, aarch64-unknown-linux-gnu, aarch64-unknown-linux-musl (edge / ARM), aarch64-linux-android (Termux).

macOS: no prebuilt binary is shipped (it would need Apple code-signing). Build from source instead — macOS is CI-tested (peer auth uses getpeereid + LOCAL_PEERPID there instead of SO_PEERCRED):

git clone https://github.com/DioNanos/mcp-crewd-rs && cd mcp-crewd-rs

cargo build --release --locked install -m755 target/release/crewd target/release/crew ~/.local/bin/

From source (any platform) — Rust ≥ 1.85:

cargo build --release

install -m 0755 target/release/crewd target/release/crew ~/.local/bin/

Engine runtime requirements: the claude engine needs Node ≥ 20 with @anthropic-ai/claude-agent-sdk installed next to the shim (cd shim && npm install); the codex engine needs the codex CLI on the daemon's PATH.

Configuration

crewd.toml (passed explicitly via --config, never cwd-derived):

runtime_dir = "/home/you/.config/crewd/runtime"   # socket, db, audit, tokens

acl_path = "/home/you/.config/crewd/acl.toml"

Optional: only for claude profiles that authenticate against an

Anthropic-compatible endpoint. A KEY=value env file holding that profile's

bearer token(s), e.g. PROVIDER_API_KEY=.... Omit for the default max.

keys_env_path = "/home/you/.config/crewd/keys.env"

acl.toml — one section per registered cell with its engine and capabilities (send, ask, reply, broadcast, read_inbox, list_cells, read_audit, spawn):

[cell.coordinator]

engine = "claude" capabilities = ["send","ask","reply","broadcast","read_inbox","list_cells","read_audit","spawn"]

Per-cell auth: a 0600 token file per cell (L0 scheme). Mount the shim in your MCP client config:

// .mcp.json (Claude Code) — one entry per cell identity

{ "mcpServers": { "crew": { "command": "crew", "args": ["mcp", "--runtime-dir", "/home/you/.config/crewd/runtime", "--cell", "coordinator", "--token-file", "/home/you/.config/crewd/coordinator.secret"] } } }

systemd

[Unit]

Description=crewd — cell fabric daemon After=network.target

[Service] Type=simple User=you Group=you

The claude shim path is resolved relative to this directory.

WorkingDirectory=/path/to/mcp-crewd-rs ExecStart=%h/.local/bin/crewd --config %h/.config/crewd/crewd.toml

IMPORTANT: the default systemd PATH does not include user-level bins.

Engine adapters spawn codex / node from the daemon's PATH:

Environment="PATH=%h/.local/bin:/usr/local/bin:/usr/bin:/bin" Restart=on-failure RestartSec=3

[Install] WantedBy=multi-user.target

Security model

• Unix socket 0600 inside a 0700 runtime dir; bind refuses symlinks.
• Kernel peer credentials checked at handshake (SO_PEERCRED on Linux/Android, getpeereid + LOCAL_PEERPID on macOS), then a per-cell token (file 0600).
• Engine children run with an exact env allowlist — secrets are read from keys_env_path by the daemon and injected only into the child that needs them; they never appear in logs or error messages.
• Append-only, hash-chained audit log (crew audit verify).
• Honest failure states: crashed/orphaned turns are recovered at boot as interrupted / failed_unknown, never silently retried after engine acceptance.

Scope honesty: processes running under the *same UID* as the daemon can read the socket and token files — crewd separates *cells*, it is not a same-user privilege boundary. See THREAT_MODEL.md.

Platform

On Termux there is no systemd: run crewd under termux-services or a plain nohup crewd --config … &. On macOS use launchd or run it in a terminal.

Docs

• SPEC.md — normative protocol & behaviour spec
• THREAT_MODEL.md — threat model and non-goals

Status

Pre-1.0 (v0.1.x): single-host fabric (UDS). Cross-host fabric, operator token CLI and warm engine reuse are on the roadmap.

License

Apache-2.0. See LICENSE.