MCP Middleware

MCP Middleware is an architectural pattern where a component intercepts standard JSON-RPC messages flowing between a host and a server.

Functions

• Security: Implementing PII masking or prompt injection protection.
• Observability: Extracting telemetry for logging and performance monitoring.
• Transformation: Modifying request/response payloads (e.g., using Goja JS interceptors).
• Reliability: Adding caching or rate-limiting.

How it's Implemented

In platforms like HasMCP Hub, middleware is applied globally or per-server to provide enterprise-grade controls without requiring modifications to the individual MCP server implementations.

Questions & Answers

What is "MCP Middleware" in a protocol context?

MCP Middleware is an architectural layer that sits between an MCP client and server. It intercepts JSON-RPC messages to perform tasks like auditing, security filtering, or data transformation without altering the core server logic.

Can you name three common use cases for MCP middleware?

Typical use cases include security (such as PII masking and prompt injection protection), observability (extracting telemetry for monitoring), and reliability (adding caching or rate-limiting to API calls).

How does HasMCP Hub leverage middleware for enterprise users?

HasMCP Hub applies middleware globally or on a per-server basis. This allows enterprise teams to enforce strict governance, security, and performance policies across all their MCP tools without needing to modify each individual server implementation.