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asyncmcp provides custom transport implementations for the Model Context Protocol that enable non-blocking, queue-based, and webhook-driven communication patterns.

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Why Async Transports?

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Traditional MCP Limitations

Standard MCP transports (stdio, Streamable HTTP) follow a synchronous request-response pattern: This works well for immediate operations but becomes problematic for:
  • Long-running computations
  • Batch processing jobs
  • External API calls with variable latency
  • Resource-intensive operations

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Async Transport Benefits

Non-Blocking

Clients can send requests and continue working while servers process asynchronously

Scalability

Distribute work across multiple workers and scale horizontally based on load

Reliability

Built-in message persistence and retry mechanisms ensure delivery

Decoupling

Clients and servers don’t need direct connections, reducing dependencies

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How Async Transports Work

Async transports separate request submission from response delivery:

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How asyncmcp Implements MCP Transports

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Custom Initialization Protocol

asyncmcp implements custom initialization protocols to establish async transport connections. Each transport uses the params field in the initialize request to communicate transport-specific configuration:
  • SQS
  • SNS+SQS
  • Webhook
  • StreamableHTTP + Webhook
The client includes its response queue URL in the initialize request:
{
  "jsonrpc": "2.0",
  "method": "initialize",
  "params": {
    "response_queue_url": "https://sqs.region.amazonaws.com/account/client-responses",
    "clientInfo": {
      "name": "example-client",
      "version": "1.0.0"
    }
  }
}
The server extracts this URL to send responses back to the client’s specific queue.

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Session Management

Each transport maintains session state through:
  • Session IDs: Unique identifiers for each client connection
  • Client IDs: Persistent identifiers across reconnections
  • Protocol versioning: Ensures compatibility between client and server
These are transmitted via transport-specific message attributes (SQS/SNS) or HTTP headers (Webhook).

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Next Steps

SQS Transport

Queue-based async messaging

Examples

See async transports in action

Proxy Server

Bridge standard clients with async transports
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