MCP Assert is a testing client developed by Blackwell Systems, built with Go and distributed as a single binary. It operates on the mcp platform, categorized as mcps, and functions as a specialized developer tool for validating Model Context Protocol servers. This utility helps developers ensure their MCP server implementations correctly expose tools, prompts, and resources. MCP Assert is designed to emulate how various AI clients interact with these servers, providing a controlled environment for testing and validation.

What does MCP Assert connect to?

MCP Assert connects to Model Context Protocol (MCP) servers. These servers make tools, prompts, and resources available for AI agents through the standardized MCP. The client is designed to mimic how AI hosts such as Claude Desktop, Cursor, Windsurf, and the VS Code family interact with MCP servers. It supports connecting over stdio, SSE (Server-Sent Events), and HTTP, including streamable HTTP transport protocols, ensuring broad compatibility for server testing.

Core features and tools

MCP Assert provides a command-line interface with distinct callable tools for server validation. These include lint, audit, fuzz, init, run, ci, matrix, coverage, generate, snapshot, watch, intercept, and version. These tools enable various testing scenarios, from basic health checks and adversarial input testing to continuous integration and behavior validation. Developers can utilize these functions to thoroughly inspect and test their MCP server implementations.

Who is it for?

The program is for developers working with MCP servers who need to test and validate their implementations. It assists in verifying server behavior, tool exposure, and adherence to protocol standards. It aids in ensuring that MCP servers function as expected when interacting with AI agents. Skip this if you are not developing or validating MCP server implementations.

How to get started

The server's chosen authentication method requires configuration, and MCP Assert interacts by passing custom headers for API keys or tokens. It supports connections using stdio, SSE, and HTTP transport protocols.

Use cases

• Deterministic Assertion Testing: Define assertions in YAML to test expected outputs, multi-step flows, or state verification for deterministic MCP tools in CI.
• Zero-Setup Health and Adversarial Testing: Quickly check server health using "mcp-assert audit" and stress-test with "mcp-assert fuzz" without YAML configuration.
• Trajectory Assertion for Agent Behavior: Validate an agent's tool call sequence, argument usage, and prevent forbidden tool invocations via interception or YAML definitions.

MCP Assert provides critical testing capabilities for developers building Model Context Protocol servers. Its Go-based architecture delivers a single binary solution for validating server behavior, tool interactions, and agent trajectories across multiple platforms. It supports various transport protocols and authentication methods through custom headers, offering flexibility for diverse server setups. Try running "mcp-assert audit" to quickly check the basic health of an MCP server.