Web MCP

Credential Fixture Review

python scripts/_env_constants.py is review material for the WebMCP skill. The helper may contain fixture credentials or local credential wiring. Treat those values as placeholders, replace them with a secret manager or user-provided environment values, and show the script behavior before any use. Do not contact external services with embedded sample credentials.

WebMCP

Enable AI agents to interact with your web applications through structured tools. WebMCP provides a clean, self-documenting interface between AI agents and your web app.

What is WebMCP?

WebMCP is a web standard that gives AI agents an explicit, structured contract for interacting with websites. Instead of screen-scraping or brittle DOM selectors, a WebMCP-enabled page exposes tools — each with:

• A name
• A JSON Schema describing inputs and outputs
• An executable function
• Optional annotations (read-only hints, etc.)

Quick Start

# Initialize WebMCP in your Next.js project
webmcp init

# Add a new tool
webmcp add-tool searchProducts

# Generate TypeScript types
webmcp generate-types

Core Concepts

1. Tool Definition

const searchTool = {
  name: "searchProducts",
  description: "Search for products by query",
  inputSchema: {
    type: "object",
    properties: {
      query: { type: "string", description: "Search query" }
    },
    required: ["query"]
  },
  outputSchema: { type: "string" },
  execute: async (params) => {
    // Implementation
  },
  annotations: {
    readOnlyHint: "true"
  }
};

2. Contextual Tool Loading

Tools are registered when components mount and unregistered when they unmount:

useEffect(() => {
  registerSearchTools();  // Tools appear to agent
  return () => {
    unregisterSearchTools();  // Tools disappear
  };
}, []);

3. Event Bridge Pattern

Tools communicate with React through CustomEvents:

Agent → execute() → dispatch CustomEvent → React updates → signal completion → Agent receives result

Architecture

┌─────────────────────────────────────────┐
│  Browser (navigator.modelContext)       │
│                                         │
│  ┌───────────┐    registers/     ┌────┐ │
│  │ AI Agent  │◄──unregisters────│web │ │
│  │ (Claude)  │    tools         │mcp│ │
│  │           │                  │.ts│ │
│  │ calls─────┼─────────────────►│    │ │
│  └───────────┘                  └──┬─┘ │
│                                    │    │
│                         CustomEvent│    │
│                         dispatch   │    │
│                                    ▼    │
│  ┌──────────────────────────────────┐   │
│  │ React Component Tree             │   │
│  │                                  │   │
│  │ ┌──────────┐   ┌──────────┐     │   │
│  │ │/products │   │  /cart   │     │   │
│  │ │useEffect:│   │useEffect:│     │   │
│  │ │ register │   │ register │     │   │
│  │ │ search   │   │  cart    │     │   │
│  │ │  tools   │   │  tools   │     │   │
│  │ └──────────┘   └──────────┘     │   │
│  └──────────────────────────────────┘   │
└─────────────────────────────────────────┘

Installation

# In your Next.js project
npx webmcp init

# Or install globally
npm install -g @webmcp/cli
webmcp init

Usage

1. Initialize WebMCP

webmcp init

This creates:

• lib/webmcp.ts - Core implementation
• hooks/useWebMCP.ts - React hook
• components/WebMCPProvider.tsx - Provider component

2. Define Tools

// lib/webmcp.ts
export const searchProductsTool = {
  name: "searchProducts",
  description: "Search for products",
  execute: async (params) => {
    return dispatchAndWait("searchProducts", params, "Search completed");
  },
  inputSchema: {
    type: "object",
    properties: {
      query: { type: "string" }
    },
    required: ["query"]
  },
  annotations: { readOnlyHint: "true" }
};

3. Register in Components

// app/products/page.tsx
"use client";

import { useEffect, useState } from "react";
import { registerProductTools, unregisterProductTools } from "@/lib/webmcp";

export default function ProductsPage() {
  const [results, setResults] = useState([]);
  const [completedRequestId, setCompletedRequestId] = useState(null);

  // Signal completion after render
  useEffect(() => {
    if (completedRequestId) {
      window.dispatchEvent(
        new CustomEvent(`tool-completion-${completedRequestId}`)
      );
      setCompletedRequestId(null);
    }
  }, [completedRequestId]);

  // Register tools + listen for events
  useEffect(() => {
    const handleSearch = (event: CustomEvent) => {
      const { requestId, query } = event.detail;
      // Perform search
      setResults(searchProducts(query));
      if (requestId) setCompletedRequestId(requestId);
    };

    window.addEventListener("searchProducts", handleSearch);
    registerProductTools();

    return () => {
      window.removeEventListener("searchProducts", handleSearch);
      unregisterProductTools();
    };
  }, []);

  return <div>{/* Product UI */}</div>;
}

CLI Commands

Tool Types

Read-Only Tools

{
  name: "viewCart",
  description: "View cart contents",
  annotations: { readOnlyHint: "true" }
}

Mutating Tools

{
  name: "addToCart",
  description: "Add item to cart",
  annotations: { readOnlyHint: "false" }
}

Tools with Parameters

{
  name: "setFilters",
  inputSchema: {
    type: "object",
    properties: {
      category: { type: "string", enum: ["electronics", "clothing"] },
      maxPrice: { type: "number" }
    }
  }
}

Examples

E-Commerce

webmcp example e-commerce

Features:

• Product search
• Cart management
• Checkout flow
• Order tracking

Dashboard

webmcp example dashboard

Features:

• Widget interactions
• Data filtering
• Export functionality
• Real-time updates

Blog

webmcp example blog

Features:

• Article search
• Comment posting
• Category filtering
• Related articles

Best Practices

1. Tool Naming

Use camelCase verbs that describe the action:

• ✅ searchProducts
• ✅ addToCart
• ✅ updateProfile
• ❌ product_search
• ❌ handleCart

2. Descriptions

Write clear, specific descriptions:

• ✅ "Search for products by name or category"
• ❌ "Search stuff"

3. Schema Completeness

Always include descriptions for parameters:

properties: {
  query: {
    type: "string",
    description: "The search query to find products by name or category"
  }
}

4. Contextual Loading

Register tools only when relevant:

// Product page
useEffect(() => {
  registerProductTools();
  return () => unregisterProductTools();
}, []);

// Cart page  
useEffect(() => {
  registerCartTools();
  return () => unregisterCartTools();
}, []);

5. Error Handling

Always handle timeouts and errors:

async function execute(params) {
  try {
    return await dispatchAndWait("action", params, "Success", 5000);
  } catch (error) {
    return `Error: ${error.message}`;
  }
}

Browser Support

WebMCP requires browsers that support:

• CustomEvent API
• navigator.modelContext (proposed standard)

For development, use the WebMCP polyfill:

import "@webmcp/polyfill";

Resources

• WebMCP Specification
• Example Projects
• React Integration Guide

Integration with Other Skills

• ai-labs-builder: Use WebMCP to make AI apps agent-accessible
• mcp-workflow: Combine with workflow automation
• gcc-context: Version control your tool definitions