"Using Claude to Check the Current Weather Without an API Key" matching MCP connectors:

Conformance checker for MCP servers. Free, no key, verdicts recomputable and re-measured daily.

oasdiffA

io.github.oasdiff

Detect breaking changes, generate changelogs, diff, and validate OpenAPI specs.

Free platform to test MCP clients without installing anything. Create mock tools with dynamic templates, configurable delays, conditions (if/then), and response sequences. Supports JSON-RPC 2.0 over Streamable HTTP. Built-in text_echo and json_echo tools. Rate-limited tiers: anonymous (5 calls/min, 1 mock tool), registered (10 calls/min, 4 mock tools), premium (60 calls/min, unlimited). Zero setup — no install, no registration required. More info: https://www.testmcp.dev

surfA

tech.geckovision

Point Gecko at an OpenAPI spec; get first-call-correct, auth-hidden agent tools.

Hosted mock REST APIs as tools: seed data, import specs, query, write, snapshot, check API status.

ship-on-friday MCP — wraps StupidAPIs (requires X-API-Key)

schrodingers-boolean MCP — wraps StupidAPIs (requires X-API-Key)

chaos-index MCP — wraps StupidAPIs (requires X-API-Key)

apology MCP — wraps StupidAPIs (requires X-API-Key)

passive-aggression MCP — wraps StupidAPIs (requires X-API-Key)

the-committee MCP — wraps StupidAPIs (requires X-API-Key)

mercury-number MCP — wraps StupidAPIs (requires X-API-Key)

excuse MCP — wraps StupidAPIs (requires X-API-Key)

corporate-apology MCP — wraps StupidAPIs (requires X-API-Key)

always-seven MCP — wraps StupidAPIs (requires X-API-Key)

JMeterA

ai.jmeter.docs

Point Claude Code, Qwen Code, Cursor, or any MCP client at https://docs.jmeter.ai/api/mcp and your agent answers JMeter questions grounded in this documentation, with a source link for every answer. Free, no API key, no signup.

JSONPlaceholder MCP — wraps JSONPlaceholder fake REST API (free, no auth)

victorian-complaint MCP — wraps StupidAPIs (requires X-API-Key)

Your DRF API as MCP tools — 1,800 endpoints become 16 dispatchers, permissioned by Django.

Search the JoJ API marketplace, read endpoint docs, and call any API with one key via one gateway.