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MCP Tester

An MCP server that returns 200 is not the same as an MCP server that works. Point this at an endpoint and it negotiates a protocol era, identifies the server, validates every tool schema, checks error handling, samples latency, and lets you call a tool by hand.

Sends requests to the endpoint you name, straight from this tab. No proxy, no relay, nothing stored. Tokens you paste go only to that server.

Endpoint

The probe negotiates a protocol era, identifies the server, lists its tools, resources and prompts, validates every tool schema, checks that unknown methods are rejected properly, and samples round-trip latency. Nothing is written to the server beyond the tool calls you make yourself.

About this tool

01 · Protocol Ladder

Negotiates modern 2026-07-28 protocol (server/discover) and falls back dynamically to legacy initialize handshakes.

Compatibility: Adapts to older and modern deployed MCP agents.

02 · Schema & Latency Checks

Validates tool JSON schemas, header annotations, method error codes (-32601), cacheability (ttlMs), and multi-sample median latency.

Diagnostic: Generates reproducible curl commands for every step.

03 · Browser-Direct Execution

Requests dispatch directly from your browser. Allows probing localhost services without intermediary proxy server risks.

Privacy: Tokens and endpoints never pass through third-party relays.

Operational Limits & Assumptions

  • · CORS Requirements: Remote endpoints must permit browser cross-origin requests. For blocked endpoints, copy the generated terminal curl.
  • · Live Execution: Tool invocations are actual live API calls. Destructive mutations on production endpoints will execute.
  • · Local Latency: Timing reflects full browser-to-server network round trips rather than isolated backend compute time.
  • · Complex Elicitation: Multi-turn human-in-the-loop elicitation pauses are surfaced as input_required.

Found a case it gets wrong? Tell me about it .