Show HN: Testing Your MCP Servers (agnost.ai)

A new developer guide and toolset for testing MCP (Model Context Protocol) servers lays out practical workflows and tooling to make MCP deployments reliable, secure, and usable by real LLMs. Key tools highlighted: MCP Inspector (official, browser-based “Postman for MCP” with default random session tokens after a March 2025 RCE fix), mcpjam Inspector (connects real models like Claude, GPT-4, Ollama and supports STDIO/SSE/HTTP transports and Docker), a Go-based MCP Tools CLI for quick terminal tests, and Google’s Chrome DevTools MCP for performance profiling. Examples and commands (npx @modelcontextprotocol/inspector, npx @mcpjam/inspector, docker run, brew/go installs) make it easy to try manual, automated, and model-driven testing. This matters because MCP servers are bridges between LLMs and real systems; failures don’t surface as stack traces but as hallucinations, wrong data, or silent cross-tenant leaks. The guide cites real 2025 incidents (SQL injection in reference implementations, multi-tenancy auth bugs) and emphasizes that LLMs produce non‑deterministic, edge-case inputs (empty strings, giant prompts, special characters), so testing must include adversarial inputs, timeouts, load (k6), and multi-tenant isolation checks. Recommended testing strategy layers range from unit tests (parameter validation, sanitization) and JSON‑RPC protocol integration tests (including known error codes) to contract tests and end‑to‑end runs against real models. CI/CD automation, observability for production behavior, and concrete security checks (SQL/command/path injection, prompt injection) round out the practical action plan for developers shipping MCP servers.