MCP Protocol Inspector & Response Debugger

Connect to a live MCP server to list and call its tools, or validate Model Context Protocol (MCP) JSON-RPC 2.0 payloads, verify content block schemas, catch protocol errors, and preview how AI clients display execution results.

Live Connection

Connect to a remote MCP server (Streamable HTTP endpoint), list its real tools, and call one — all proxied server-side, so CORS never blocks you. Works with any public HTTP MCP endpoint.

Or validate a payload
Load Sample Protocol Payloads

Protocol Diagnostic Report

Valid Protocol Format
JSON Syntax
Valid JSON format.
JSON-RPC Specification
Header contains jsonrpc: "2.0".
Content Block Structure
Found array of 1 content item(s).
Execution Status
isError is set to false (Clean execution).

Visual AI Client Preview

Simulates how Claude Desktop, Cursor, and Windsurf render this tool output in their chat stream.

AI Client Tool Execution Window
MCP Transport: Stdio / SSE
Content Block #1 — [text]
Successfully processed 42 records. Database migration completed in 140ms.

Understanding Model Context Protocol JSON-RPC Specifications

The Model Context Protocol communicates over standard JSON-RPC 2.0 transports (stdio pipes or Server-Sent Events). When an AI client like Claude Desktop, Cursor, or Windsurf calls a tool or queries a resource, it expects responses to adhere strictly to protocol schemas.

Common integration issues — such as missing content arrays, unhandled base64 image strings, or omitted mimeType headers — can cause AI clients to silently drop tool outputs or fail turns. Use this diagnostic inspector during development to verify payload compliance instantly.

Frequently Asked Questions (FAQ)

Paste any JSON-RPC request or tool execution response payload into the inspector above. The diagnostic engine checks specification compliance (jsonrpc: "2.0", content array structures, MIME types, isError flags) and renders a live visual preview of how AI clients display the result.