MCP Server Test Harness

Example Use Cases

• 1

  Fast, reliable in-memory testing of MCP servers without subprocess overhead.

• 2

  Assert on MCP tool calls, resources, and prompts in automated test suites.

• 3

  Test compiled MCP servers via subprocess with access to stderr for debugging.

Description

mcp-harness provides a fast, in-memory test harness for MCP servers, allowing direct connection to McpServer instances without the need for child processes, ports, or IO. It simplifies testing by enabling instant startup and easy assertions on tool calls, resources, and prompts. The toolkit supports both in-memory and subprocess modes, making it flexible for different testing scenarios and integrates well with popular test frameworks through assertion helpers.