bus-mcp

An ergonomic MCP server fronting the self-hosted AlphaHive coordination bus (backend/coordination_bus.py in the alphahive repo) -- so a Claude agent calls claim_lane("feeds-refactor", owner="session-A") instead of hand-rolling curl -X POST .../lanes/feeds-refactor/claim -d '{...}'. Built to the desktop-mcp/github-mcp standard (own pyproject, fastmcp server, honest README, real test suite) -- this is that exact "MCP over an HTTP API" pattern turned on our own self-hosted API.

Quickstart (60 seconds)

pip install bus-mcp

Add to your Claude Desktop/Code MCP config:

{
  "mcpServers": {
    "bus-mcp": {
      "command": "bus-mcp"
    }
  }
}

No console script on PATH? Fall back to "command": "python", "args": ["-m", "bus_mcp"]. By default this talks to a bus at http://127.0.0.1:8100/api/bus -- see "Env vars" below to point it elsewhere.

What this is / is not

This fronts a private, localhost-only, no-auth v1 coordination substrate -- not a public service. The bus itself is a blackboard (append-only messages) + a lane-claim registry (task-queue leases with steal-on-expiry) + a status rollup for a command-center panel. It executes nothing outward-facing: action_flag on a message is recorded and displayed only, never acted on by the bus. bus-mcp adds zero new capability over what the bus already does via curl -- it only makes the six routes ergonomic MCP tools with typed inputs and typed errors instead of raw HTTP.

Tools

No write-safety knob here the way github-mcp has one for real external writes -- every bus route is coordination-only (store/display/claim). As of coordination-bus v1.1, the bus MAY optionally require a shared secret on its 4 write routes (default off); this client mirrors that with zero new config surface of its own -- see "Write-secret auth (v1.1)" below.

Typed errors, never a raw crash

Every tool returns {"ok": true, ...} on success or {"ok": false, "error": {...}} on failure -- never an unhandled exception or stack trace.

• bus_unreachable -- connection refused, timeout, or DNS failure. Means the AlphaHive backend isn't running, or is running without the bus routes loaded (backend/coordination_bus.py mounted on :8100).
• bus_api_error -- the bus responded with a 4xx/5xx. Carries status_code + the bus's own detail text -- e.g. a 409 lane-conflict message telling you who holds the lane and for how long.

Internally, bus_mcp/client.py raises typed BusUnreachable / BusApiError exceptions; bus_mcp/routes.py catches both and normalizes to the dict shape above before a tool ever returns. Tests exercise both layers.

Env vars

Write-secret auth (v1.1)

The coordination bus can optionally gate its 4 write routes (post_message, claim_lane, release_lane, heartbeat_lane) behind a shared secret header (X-Bus-Secret), read from BUS_WRITE_SECRET on the bus side. This client reads the same env var name from its own process and, when set, bus_mcp/client.py's post() attaches the header to every write call -- bus_mcp/routes.py and every tool caller stay unaware of arming state entirely. client.get() never attaches the header (GET routes are never gated bus-side).

To use with an armed bus: set BUS_WRITE_SECRET to the same value in both the AlphaHive backend's environment and this MCP server's environment (e.g. in the config that launches run_server.py), then restart both processes. If the value is missing or wrong, a write tool call returns the normal {"ok": false, "error": {"type": "bus_api_error", "status_code": 401, ...}} shape -- no special-casing needed, it flows through the same typed BusApiError path as any other 4xx.

Unset (default): no header is sent, identical to talking to a bus that has never been armed -- zero behavior change from pre-v1.1.

Lease ceiling surfacing (coordination-bus v1.3+)

The bus supports an operator-configurable ceiling on granted lease durations (BUS_MAX_LEASE_SECONDS, bus-side): a claim_lane/heartbeat_lane request for lease_s=7200 may be silently clamped to a shorter effective grant (e.g. 3600s) rather than rejected -- see coordination_bus.README.md's "v1.3 - configurable lease ceiling" section in the alphahive repo for the full server-side story.

This client surfaces both halves of that contract, additively:

• claim_lane / heartbeat_lane responses include a top-level lease_s field on ok=True -- the EFFECTIVE (post-clamp) duration actually granted. Always check this rather than assuming the requested lease_s was honored in full; a caller that ignores it and heartbeats on its own optimistic schedule risks its lane going stale early.
• get_bus_status exposes _meta.max_lease_seconds -- the currently configured ceiling, so a caller can check before it even claims.

Both fields are pure passthrough: bus_mcp/routes.py merges the bus's raw JSON response into the tool result ({"ok": True, **result}), so no client-side code change was needed to carry these new fields -- only the tool descriptions (below) and test coverage locking the behavior in both directions. Version-tolerant by construction: against a pre-v1.3 bus that omits these fields entirely, the tool result simply lacks lease_s / max_lease_seconds -- never a crash, never a synthesized default.

No client-side ceiling caching/pre-flight warning is implemented -- this client holds no state between calls (every tool call is a fresh httpx request), so there is nothing to check a requested lease_s against locally before the round-trip. A caller that wants to avoid a surprise clamp should call get_bus_status first and compare its own lease_s request against _meta.max_lease_seconds.

Usage examples

Once connected in a Claude session, an agent can:

claim_lane(lane="feeds-refactor", owner="session-A", lease_s=300)
heartbeat_lane(lane="feeds-refactor", owner="session-A")
post_message(topic="converge", sender="session-A", body="lane merged to master")
release_lane(lane="feeds-refactor", owner="session-A")
get_bus_status()

Testing

.venv/Scripts/python.exe -m pytest -q

CI (.github/workflows/ci.yml) runs this suite on every push/PR and fails the build if the Tests badge above drifts from what the suite actually reports -- see scripts/check_readme_counts.py.

All HTTP is mocked via respx -- the full suite never depends on a live bus. One additional test, tests/test_live_smoke.py::test_live_get_bus_status_returns_rollup, is gated behind BUS_MCP_LIVE=1 and calls a real running bus's get_bus_status route. As of this writing the bus routes are dormant/404 on the live :8100 AlphaHive backend until the operator restarts it with coordination_bus.py's router mounted -- so that one gated test is expected to skip (or fail if forced) until that restart happens. That is correct behavior, not a bug in this repo.

Install / connect

python -m venv .venv
.venv/Scripts/python.exe -m pip install -e ".[test]"

Registered in ~/.claude.json under mcpServers.bus-mcp as a stdio server invoking run_server.py by absolute path (no cwd needed -- the entrypoint adds its own directory to sys.path).

Handshake check

.venv/Scripts/python.exe scripts/list_tools.py

Prints the six registered tool names with no transport started -- pure introspection, useful for verifying the server wires up cleanly after any change.

Out of scope