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MCP Tool Tester

Validate a WebMCP tool definition's name, description and inputSchema, generate a test form from the schema, and mock a call locally.

MCP Tool Tester

Definition editor

Validation

✓ Valid

✓ All checks passed — definition is valid.

0 errors · 0 warnings · 0 info

Mock execution

Agent sends:
{
  "name": "searchProducts",
  "arguments": {
    "query": "wireless headphones",
    "limit": 5,
    "category": "electronics"
  }
}
Tool returns:
{
  "content": [
    {
      "type": "text",
      "text": "Mock response for tool 'searchProducts' with inputs: {\"query\":\"wireless headphones\",\"limit\":5,\"category\":\"electronics\"}"
    }
  ]
}

Integration guidance

Use this definition directly in browser integrations. For production discovery, publish a manifest at /.well-known/webmcp.json.

navigator.modelContext?.registerTool?.({
  "name": "searchProducts",
  "description": "Search the product catalog by keyword, category, and result limit.",
  "inputSchema": {
    "type": "object",
    "properties": {
      "query": {
        "type": "string",
        "description": "Search query string"
      },
      "limit": {
        "type": "number",
        "description": "Maximum number of results to return"
      },
      "category": {
        "type": "string",
        "description": "Product category filter",
        "enum": [
          "electronics",
          "books",
          "clothing",
          "home"
        ]
      }
    },
    "required": [
      "query"
    ]
  }
});
Need to build tool schemas visually?AI Tool Schema Builder →
Browse MCP servers for AI tool integration?MCP Server Directory →

Updated . Provided as is. Check the output before you rely on it in production.

How to use MCP Tool Tester

  1. 1

    Paste a tool definition

    Paste the object you pass to navigator.modelContext.registerTool(), with name, description and inputSchema, or load a sample.

  2. 2

    Fix validation findings

    Errors flag missing fields and invalid schemas; warnings flag long descriptions and a missing required array.

  3. 3

    Run a mock call

    Fill the form generated from the inputSchema and execute to see the request an agent would send and the response envelope.

  4. 4

    Preview discovery

    See how the tool appears to an agent enumerating navigator.modelContext.tools, then copy or download the definition.

Questions and answers

What is MCP Tool Tester?
An MCP or WebMCP tool definition is the JSON (name, description and inputSchema) an AI agent reads to decide when and how to call a tool. This tester checks it against a set of lint rules, builds a test form from the schema, mocks a call and previews discovery. It uses the same engine as WebMCP Playground.
Does it call my real tool?
No. Execution is mocked locally so you can check the request shape without running anything.
Is my definition uploaded?
No. Validation and the mock run entirely in your browser.
For AI agents: how to call this tool

Machine-readable contract, endpoints and examples. Humans can ignore this section.

Best Path For Builders

Browser workflow

Runs instantly in the browser with private local processing and copy/export-ready output.

Browser Workflow

This tool is optimized for instant in-browser execution with local data handling. Run it here and copy/export the output directly.

/mcp-tool-tester/

For automation planning, fetch the canonical contract at /api/tool/mcp-tool-tester.json.