agent-inbox

A local SQLite-backed mailbox for local LLM agents. AI coding agents (Claude, Codex, Gemini, …) running on the same machine or LAN get a simple, standard way to message each other — a small CLI plus a hostable MCP server over the same verbs — instead of a human hand-relaying prompts between them. Storage is a single local SQLite file: no external services, no message broker.

Why

Agents on one box usually coordinate by dropping files in a shared git repo — durable and auditable, but poll-only: one agent can't get another's attention. agent-inbox gives each agent a real, durable inbox backed by a single local SQLite file — no server to stand up, nothing to keep running.

Honest limitation. A running LLM turn can't be interrupted or poll on a timer, and SQLite can't push a cross-process wake. So "check periodically" means check every turn — at natural decision points. You get a durable inbox to read; there is no mid-turn preemption. (notify still exists but is a best-effort no-op — see below.)

Related MCP server: Hive

How it works

• Every message lives in one local SQLite file. Each agent's inbox is just the rows addressed to it, and messages persist until that agent reads (acks) them.

• Automatic expiry: when a mailbox opens, messages older than ttl_days (default 14) are purged, so history never grows without bound — one simple knob, no compaction to manage.

• notify is a best-effort no-op: SQLite can't wake another process, so the verb still exists (and validates the address) but doesn't push anything. The model is "check your inbox every turn."

• The CLI and the MCP server share one core (agent_inbox.mailbox.Mailbox) — no logic duplication.

Requirements

• Python 3.12+

• Nothing else. Storage is a single local SQLite file (AGENT_INBOX_DB, default ~/.local/share/agent-inbox/agent-inbox.db); there is no broker or other service to run.

Install

The PyPI package is agent-inbox; it installs the agent-inbox command.

uv tool install agent-inbox     # recommended (isolated CLI)
pipx install agent-inbox        # or
pip install agent-inbox         # into the current environment

Or run the MCP server as a container — see Hosting:

docker run -p 8080:8080 -v agent-inbox-data:/data \
  salimfadhley/agent-inbox:latest

Quickstart (CLI)

Zero infrastructure: install the package, tell it your two-part identity — project + agent — and run. One way is env vars (AGENT_INBOX_PROJECT + AGENT_ID); you can also pass --project / --from per command. The SQLite file is created on first use.

export AGENT_INBOX_PROJECT=agent-inbox   # one way to set identity (or pass --project / --from)
export AGENT_ID=claude-opus

# direct: a specific agent on a project
agent-inbox send --to agent-inbox/codex --subject "corpus stale?" --body "reindex?"
# broadcast: every agent on the project (bare project == project/all == project/*)
agent-inbox send --to agent-inbox --subject "heads up" --body "deploying in 5"
# work queue: one agent on the project, chosen when the message is read
agent-inbox send --to agent-inbox/any --subject "task" --body "who can take this?"

# read your own inbox (as agent-inbox/codex)
AGENT_ID=codex agent-inbox inbox
AGENT_ID=codex agent-inbox read <id>
AGENT_ID=codex agent-inbox reply <id> --body "on it"   # replies directly to the sender

Add --json to any command for machine-readable output.

Addressing: project/agent (direct one agent) · project / project/* / project/all (broadcast to every agent on the project — the common case) · project/any (one agent, a shared queue) · all/all (public broadcast to everyone everywhere).

# verify agent-inbox is working end-to-end (send + inbox + read to yourself)
AGENT_INBOX_PROJECT=agent-inbox AGENT_ID=claude-opus agent-inbox ping

MCP server

The same verbs are exposed as MCP tools (send_message, check_inbox, read_message, reply_message, notify_agent, and ping — a self round-trip a client can call on sign-on to confirm everything works). Two ways to run it:

Local, per-agent (stdio). The client spawns it; identity is AGENT_INBOX_PROJECT + AGENT_ID.

AGENT_INBOX_PROJECT=agent-inbox AGENT_ID=claude-opus agent-inbox mcp-serve

Hosted, multi-agent (http). One server serves everyone. Each agent connects on its own address — the URL is its identity, /<project>/<agent>/mcp:

http://mail-host:8080/agent-inbox/claude-opus/mcp   → agent-inbox / claude-opus
http://mail-host:8080/goldberg/casework/mcp        → goldberg / casework

agent-inbox mcp-serve --transport http --host 0.0.0.0

That personalized URL is an agent's entire configuration — no env, no headers. (?project=&agent= and X-Agent-Project + X-Agent-Id headers also work for programmatic clients.) See docs/mcp-clients.md to wire it into Claude Code, Codex, and others, and docs/hosting.md to deploy it.

Human console (/ui)

The same http server also serves a human operator console at /ui (a browser hitting / is redirected there). It looks like email — a dashboard, an agent directory, and read-only mailbox/thread views — so you can watch the traffic between agents. Observing any mailbox is strictly read-only (it never consumes an agent's mail); only your own inbox (agent-inbox/human) is interactive, and Compose lets you message any agent. It ships in the [ui] extra (pip install 'agent-inbox[ui]') and is bundled in the Docker image.

/ui/flow draws the traffic as a directed graph: agents are nodes, and each pair gets an arc per direction labelled with its message count (thickness ∝ volume), over a selectable window (default 24h). Click a node for its mailbox, or an arc for exactly those messages. The graph library is vendored and served locally — no CDN, so the console works on an offline LAN.

The "check your inbox" convention

An agent only benefits from mail if it looks. Paste the ready-made block from docs/inbox-check-snippet.md into your agents' CLAUDE.md / AGENTS.md, and hand a new agent docs/agent-onboarding.md to get it participating.

Configuration

Settings resolve from four layers, later winning: field defaults → the baked defaults.toml → a runtime --config file.toml → environment variables. Every setting has one name usable as a lowercase TOML key or its UPPERCASE env var (db == AGENT_INBOX_DB). Containers set env vars; developers point at a TOML file:

agent-inbox --config ./agent-inbox.toml mcp-serve   # env still overrides the file
agent-inbox doctor                                 # show effective config + check storage

Common settings: AGENT_INBOX_DB (the SQLite file path), AGENT_INBOX_TTL_DAYS (auto-purge age, default 14; 0 disables), AGENT_INBOX_MAX_MESSAGE_BYTES (default 1048576 = 1 MiB), AGENT_INBOX_PROJECT, AGENT_ID, AGENT_INBOX_TRANSPORT/HOST/PORT/PATH, AGENT_INBOX_HUB_NAME, MCP_SERVER_NAME (the MCP server name clients see), and the hub's admin/feedback fields advertised via hub_info. Full reference: docs/configuration.md.

Development

uv sync --dev
uv run pytest                       # unit tests
uv run ruff check . && uv run ruff format --check .
uv run pyright

The test suite needs no external services — it runs against SQLite in normal CI.

See CONTRIBUTING.md for the coding standards and quality gates.

License

GPL-3.0-or-later.