rabbit-mcp

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An MCP server for RabbitMQ built on message contracts (.NET 10). Each contract becomes a typed tool whose input schema is the contract itself. Messages use the MassTransit wire format, so MassTransit services receive them as they are; services without MassTransit get plain JSON. The server itself does not depend on MassTransit.

• Send: publish_<contract> and request_<contract>, validated against the contract first.

• See: queues, messages (with fault details) and who consumes each contract.

• Recover: move messages from _error queues back, fix and resend them, or park poison messages. Nothing is ever deleted.

• Answer: in responder mode the model answers requests sent by your services.

• Protect: contracts diff catches wire-breaking changes in CI; roles, rate limits and audit for teams.

Install

claude mcp add rabbit-mcp \
  -e RabbitMcp__Uri=amqp://guest:guest@localhost:5672/ \
  -e RabbitMcp__EnablePublish=true \
  -- /full/path/to/rabbit-mcp

Claude Desktop: the same as "command" and "env" in claude_desktop_config.json. Local RabbitMQ: docker compose up -d.

Try it: samples/Shop starts RabbitMQ, PostgreSQL, a MassTransit shop and rabbit-mcp with one command, and walks through orders, error recovery and approvals.

Related MCP server: foral

Tools

Results are structured (outputSchema); errors say what to do next. Prompts diagnose_errors, investigate_message, review_approvals and contract_health walk through common tasks, and every contract is a resource contract://<Name>.

Contracts

// Event → publish_payment_captured
[MessageContract("Payment was captured by the PSP.", Version = 1)]
public sealed record PaymentCaptured
{
    [Description("Order the payment belongs to.")]
    public required Guid OrderId { get; init; }

    [Range(typeof(decimal), "0.01", "1000000")]
    public required decimal Amount { get; init; }
}

// Request → request_get_order_status
[MessageContract("Asks for the current status of an order.",
    Responses = new[] { typeof(OrderStatus), typeof(OrderNotFound) })]
public sealed record GetOrderStatus
{
    public required Guid OrderId { get; init; }
}

• required, nullability, [Description] and DataAnnotations go into the schema and are enforced.

• Names follow MassTransit (urn:message:Namespace:Type, exchange Namespace:Type); Urn and Exchange override them.

• Your contracts: a class library referencing the RabbitMcp.Contracts package, loaded with RabbitMcp__ContractAssemblies=/path/Billing.Contracts.dll.

Services without MassTransit — Format = MessageFormat.Raw: the body is plain JSON, metadata goes into AMQP properties, and you set Exchange and/or RoutingKey. Requests use RabbitMQ RPC (reply_to + correlation_id; the reply type in the AMQP type).

[MessageContract("Asks the shipping desk for a quote.", Format = MessageFormat.Raw, RoutingKey = "shipping-quotes",
    Responses = new[] { typeof(ShippingQuote), typeof(ShippingUnavailable) })]
public sealed record GetShippingQuote { … }

Without C# (AsyncAPI) — RabbitMcp__ContractFiles=warehouse.yaml: every message of an AsyncAPI 3.0 or 2.x file becomes a tool with the file's JSON Schema; routing comes from the AMQP bindings, x-rabbit-mcp: { format: masstransit } for MassTransit services. Example: samples/asyncapi/warehouse.yaml. rabbit-mcp contracts asyncapi Billing.Contracts.dll exports C# contracts.

Compatibility check — compare two builds (or two AsyncAPI files) in CI; exit code 1 on breaking changes:

rabbit-mcp contracts diff old/Billing.Contracts.dll new/Billing.Contracts.dll
# BREAKING OrderPlaced customer: Type changed from string to number.
# WARNING  OrderPlaced: Breaking change without a version bump (still v1).

Request/response

request_<contract> waits for the reply (timeout 1–120 s) and returns responded, faulted or timeout, with the reply checked against its contract.

Responder: RabbitMcp__RespondTo=ApproveLargeOrder lets your service ask and the model answer. Requests appear in pending_requests; the model answers with reply_<response> or reject_request (the requester gets a RequestFaultException). Requests are kept in memory; one instance per ClientName answers, others stand by.

For teams (HTTP)

RabbitMcp__Transport=http serves /mcp (and /healthz). It refuses to start without authentication:

• API keys: RabbitMcp__ApiKeys="alice:KEY1;ci:KEY2" (≥ 32 characters); clients send X-Api-Key.

• JWT / OIDC: RabbitMcp__JwtAuthority + RabbitMcp__JwtAudience.

docker run -d -p 5080:5080 \
  -e RabbitMcp__Uri=amqp://user:pass@rabbit:5672/ \
  -e RabbitMcp__ApiKeys="team:$(openssl rand -base64 32)" \
  -e RabbitMcp__ContractAssemblies=/contracts/Billing.Contracts.dll -v ./contracts:/contracts:ro \
  ghcr.io/lazogio/rabbit-mcp:1.0

Roles (HTTP only; without roles every caller may use every enabled tool):

RabbitMcp__Roles__viewer="read"
RabbitMcp__Roles__operator="read;publish:Order*;request;republish:*_error"
RabbitMcp__UserRoles="alice=operator;ci=viewer"
RabbitMcp__DefaultRoles="viewer"

Permissions: read, publish, request, republish, respond, *; patterns limit them by contract or queue. Users are matched by API key name, token user or the JWT roles claim. Callers see only the tools they may use, and each call is checked again.

Configuration

Environment variable RabbitMcp__<Option> or appsettings.json. Lists are ;-separated, * is a wildcard.

OpenTelemetry: set OTEL_EXPORTER_OTLP_ENDPOINT; traces join the MassTransit consumer's trace.

Guarantees

• No silent loss: invalid messages are not sent; publisher confirms and mandatory turn an undeliverable message into an error.

• Safe moves: a message leaves the error queue only after the broker confirmed its new copy; the body never changes.

• Nothing is deleted: poison messages are parked with every header, and can be brought back.

• A person confirms: clients with MCP elicitation (e.g. Claude Code) show a dialog before anything moves; stateless HTTP falls back to confirm=true.

• Audited: every send, move and answer — including refused ones — with the user.

• Untrusted content: message headers never redirect where messages go; passwords never appear in logs or errors.

License

MIT. Development, tests and releases: CONTRIBUTING.md.