MCP Lab / open-source testing tools

Test MCP timeout, cancellation, and disconnect handling.

MCP Lab develops focused tools for reproducing failure conditions in Model Context Protocol systems. The first project, MCP Failure Lab, runs deterministic scenarios against a purpose-built MCP server.

Getting startedGitHub repository
Usable early releaseMIT licensedNode.js 22.19+stdio transport

A scenario and its result

The runner makes a real MCP tool call, records the observed outcome and duration, then evaluates the declared expectations.

delay-success.jsoninput
{
  "name": "bounded delay succeeds",
  "call": {
    "tool": "delay",
    "args": { "delayMs": 250 }
  },
  "timeoutMs": 1000,
  "expect": {
    "outcome": "success",
    "maxDurationMs": 500
  }
}
consoleoutput
$ npm run dev -- run \
  examples/scenarios/delay-success.json

Scenario:   bounded delay succeeds
Outcome:    success
Duration:   ~250 ms
Assertions: passed

MCP Failure Lab

The current release covers a deliberately small set of failure modes and reporting primitives.

CapabilityBehaviorStatus
delayBounded, cancellation-aware latency from 0 to 30 seconds.available
hangA pending request that ends only on client cancellation.available
disconnectTransport loss while a tool request is in flight.available
pingHealth and post-condition verification through a separate tool path.available
reportingConsole and stable JSON output with CI-oriented exit codes.available
HTTP / JUnitStreamable HTTP transport and JUnit reports.planned
Project detailsDocumentation

What it is

A deterministic test server, scenario runner, assertion model, and CLI for exercising known MCP failure paths.

What it is not

It is not currently a general-purpose proxy, protocol compliance suite, or external MCP client orchestrator.