MCP Hello World Server

The MCP Hello World server is a deliberately lightweight, TypeScript‑based implementation of the Model Context Protocol (MCP). Its primary purpose is to act as a test double or mock server for developers building and validating MCP clients. By providing a controlled, predictable environment that mimics the essential aspects of an MCP server, it removes external dependencies and network variability from unit or integration tests.

In practice, the server exposes a minimal set of tools—most notably and . These tools have deterministic behaviors: the tool simply returns the input it receives, while logs diagnostic information. Because their outputs are fixed and straightforward, tests can assert against them with confidence, ensuring that client logic handles request formatting, response parsing, and error handling correctly without being influenced by the complexities of a real AI backend.

The server supports both STDIO and HTTP/SSE transport protocols. This dual‑mode capability allows developers to exercise client code under different connection scenarios, from simple command‑line interactions to full HTTP streaming. The startup time is minimal, and the dependency footprint is small, making it ideal for frequent use in continuous integration pipelines where speed and reliability are paramount.

Typical use cases include:

• Unit testing of MCP client libraries, where the focus is on request construction and response handling rather than backend intelligence.
• Integration testing of higher‑level application components that rely on MCP, ensuring that they behave correctly when the protocol layer is present but the underlying model is mocked.
• Debugging of client implementations by running the server manually and inspecting its responses with tools such as MCP Inspector.

Because it is not intended for production, the server deliberately omits advanced features like authentication, rate limiting, or complex toolchains. This simplicity is a feature: it guarantees that tests run consistently and that any failures are attributable to client code rather than environmental noise. For developers who need a quick, dependable MCP environment during development or testing, the MCP Hello World server offers an elegant solution that bridges the gap between real-world protocol interactions and controlled test conditions.