@msfeldstein/mcp-test-servers
MCP ServerFreeA collection of MCP test servers including working servers (ping, resource, combined, env-echo) and test failure cases (broken-tool, crash-on-startup)
Capabilities7 decomposed
mcp server lifecycle testing with working reference implementations
Medium confidenceProvides a suite of minimal but fully functional MCP server implementations (ping, resource, combined, env-echo) that demonstrate correct protocol compliance and server initialization patterns. Each server implements the MCP specification's required message handlers and resource/tool registration flows, allowing developers to validate their MCP client implementations against known-good server behavior without external dependencies.
Bundles multiple working MCP server implementations in a single npm package with explicit protocol compliance focus, eliminating the need to build test servers from scratch or rely on external services for MCP client validation
Faster iteration than building custom test servers from scratch and more reliable than testing against production MCP servers that may have different behavior or availability constraints
intentional mcp server failure case simulation
Medium confidenceIncludes deliberately broken server implementations (broken-tool, crash-on-startup) that trigger specific failure modes and error conditions defined in the MCP specification. These servers allow developers to validate error handling paths in their MCP clients by reproducing edge cases like malformed tool definitions, unhandled exceptions during initialization, and protocol violations without needing to manually craft error scenarios.
Provides pre-built failure scenarios as executable servers rather than mock objects or test fixtures, enabling integration-level testing of error handling paths with actual protocol-level failures
More realistic than unit test mocks because it exercises the full MCP protocol stack including connection handling and message serialization, while being more controlled than testing against real-world servers
resource serving and content delivery via mcp protocol
Medium confidenceImplements the MCP resource capability, allowing test servers to expose named resources (files, data, or computed content) that clients can request and retrieve through the MCP protocol. The resource server maintains a registry of available resources with metadata and serves content on-demand, demonstrating the resource discovery and retrieval patterns defined in the MCP specification.
Implements resource serving as a first-class MCP capability with proper metadata registration and discovery patterns, rather than treating resources as a secondary feature or mock data
Demonstrates the full resource lifecycle (discovery, metadata, retrieval) in a single working server, whereas most MCP examples focus only on tool calling
tool definition and invocation testing via mcp protocol
Medium confidenceProvides working tool implementations that register themselves with the MCP protocol, accept tool invocation requests from clients, and return results in the correct format. The combined server demonstrates multiple tools with different signatures and return types, allowing clients to validate tool discovery, parameter validation, and result handling against a known-good implementation.
Bundles multiple tool implementations with varying complexity and parameter types in a single server, enabling comprehensive testing of tool calling patterns without building custom tools
More complete than simple echo tools because it includes tools with different signatures and return types, providing better coverage of real-world tool calling scenarios
environment variable exposure and echo via mcp
Medium confidenceThe env-echo server reads environment variables from the host process and exposes them through the MCP protocol, allowing clients to retrieve environment configuration without direct system access. This demonstrates how MCP servers can bridge between system state and protocol clients, useful for testing clients that need to access host configuration or validate environment-aware behavior.
Bridges system environment state into the MCP protocol layer, demonstrating how servers can expose host configuration as a first-class MCP capability rather than hardcoding values
More realistic than mock servers because it uses actual environment variables, enabling testing of environment-aware client behavior in different deployment contexts
ping/heartbeat server for connection validation
Medium confidenceImplements a minimal MCP server that responds to ping requests with pong responses, providing the simplest possible working MCP server implementation. This server validates basic protocol compliance, connection establishment, and message round-trip functionality without any complex features, serving as a baseline for testing MCP client connectivity and protocol parsing.
Provides the absolute minimal MCP server implementation, useful as a reference for understanding the core protocol without distraction from feature implementations
Simpler and faster to test against than full-featured servers, making it ideal for isolating connection and protocol parsing issues
combined multi-capability mcp server for integration testing
Medium confidenceBundles multiple MCP capabilities (tools, resources, and other features) into a single server instance, allowing clients to test interactions between different capability types and validate that the client correctly handles servers with mixed feature sets. This server demonstrates how real-world MCP servers typically expose multiple capabilities simultaneously.
Combines multiple MCP capabilities in a single server instance, providing a more realistic testing environment than single-capability servers while remaining simple enough to understand
More representative of real-world MCP servers than single-capability test servers, enabling better validation of client behavior in production scenarios
Capabilities are decomposed by AI analysis. Each maps to specific user intents and improves with match feedback.
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servers
Model Context Protocol Servers
Best For
- ✓MCP client library developers building SDKs or frameworks
- ✓Teams integrating MCP into existing AI applications
- ✓Protocol implementers validating spec compliance
- ✓MCP client library developers implementing robust error handling
- ✓QA teams building comprehensive test suites for MCP integrations
- ✓Developers implementing fallback and recovery strategies for MCP failures
- ✓Developers building MCP clients that consume resources from servers
- ✓Teams implementing resource-based MCP servers
Known Limitations
- ⚠Servers are intentionally minimal — do not include production features like authentication, rate limiting, or error recovery
- ⚠No persistence layer — all state is ephemeral and reset on server restart
- ⚠Single-threaded execution model — not suitable for load testing or concurrent client scenarios
- ⚠Failure modes are static and predefined — cannot simulate dynamic or intermittent failures
- ⚠No timing control — cannot reproduce race conditions or timeout-related issues
- ⚠Limited to the specific failure scenarios included in the package
Requirements
Input / Output
UnfragileRank
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Package Details
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A collection of MCP test servers including working servers (ping, resource, combined, env-echo) and test failure cases (broken-tool, crash-on-startup)
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