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MCP Server Tester

Generate and validate MCP (Model Context Protocol) JSON-RPC payloads. Build tool call requests, inspect schemas, and test your MCP server implementation.

✓ JSON-RPC payload generator ✓ Tool schema validator ✓ MCP lifecycle simulator

MCP Method

Tool Definition Builder

Build a valid MCP tool definition to validate your server's schema format.

Generated Payload

   
 
MCP Lifecycle Sequence
 
 
            <div class="flex items-start gap-2 text-xs">
              <span class="w-5 h-5 rounded-full bg-primary/20 text-primary flex items-center justify-center font-semibold flex-shrink-0">1</span>
              <div><span class="font-mono text-primary">initialize</span><span class="text-text-muted ml-2">Handshake + capabilities negotiation</span></div>
            </div>
          
            <div class="flex items-start gap-2 text-xs">
              <span class="w-5 h-5 rounded-full bg-primary/20 text-primary flex items-center justify-center font-semibold flex-shrink-0">2</span>
              <div><span class="font-mono text-primary">initialized (notify)</span><span class="text-text-muted ml-2">Client confirms ready</span></div>
            </div>
          
            <div class="flex items-start gap-2 text-xs">
              <span class="w-5 h-5 rounded-full bg-primary/20 text-primary flex items-center justify-center font-semibold flex-shrink-0">3</span>
              <div><span class="font-mono text-primary">tools/list</span><span class="text-text-muted ml-2">Discover available tools</span></div>
            </div>
          
            <div class="flex items-start gap-2 text-xs">
              <span class="w-5 h-5 rounded-full bg-primary/20 text-primary flex items-center justify-center font-semibold flex-shrink-0">4</span>
              <div><span class="font-mono text-primary">tools/call</span><span class="text-text-muted ml-2">Invoke a specific tool</span></div>
            </div>
          
            <div class="flex items-start gap-2 text-xs">
              <span class="w-5 h-5 rounded-full bg-primary/20 text-primary flex items-center justify-center font-semibold flex-shrink-0">5</span>
              <div><span class="font-mono text-primary">ping</span><span class="text-text-muted ml-2">Keep-alive (optional)</span></div>
            </div>
           
 
 
 
 
Frequently Asked Questions
What is MCP (Model Context Protocol)?▼
MCP is an open protocol by Anthropic that standardizes how AI models connect to external tools, data sources, and services. An MCP server exposes tools (functions), resources (data), and prompts to AI clients like Claude Desktop, Cursor, and custom agents. It uses JSON-RPC 2.0 over stdio or HTTP/SSE.
How do I build an MCP server?▼
Use the official MCP SDKs: @modelcontextprotocol/sdk for TypeScript/Node.js, or mcp Python package. Define tools with input schemas, implement handlers, and start a server. For stdio servers: `npx @modelcontextprotocol/sdk`. For HTTP servers: expose a /sse endpoint. Register your server in the MCP client config.
What is the difference between tools and resources in MCP?▼
Tools are callable functions with defined input schemas — they perform actions (search, calculate, write). Resources are read-only data sources identified by URIs (files, database rows, API responses). Prompts are pre-defined conversation templates. Most custom MCP servers primarily expose tools.
How do I test an MCP server locally?▼
Use the MCP Inspector (npx @modelcontextprotocol/inspector), Claude Desktop with local config, or build a simple test client. For HTTP servers, you can test the /list endpoint manually. This tool generates valid MCP JSON-RPC payloads you can send directly to test your server's protocol compliance.
What transports does MCP support?▼
MCP supports two transports: (1) stdio — the server runs as a subprocess and communicates via stdin/stdout, used by most desktop clients. (2) HTTP with SSE — server exposes HTTP endpoints for server-sent events, better for remote/cloud deployments. Most local development uses stdio for simplicity.
 
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