WebMCP

WebMCP - Enable AI agents to interact with your web applications through structured tools. Implements the WebMCP standard for Next.js/React apps with tool registration, event bridge pattern, and contextual tool loading. Use when building AI-agent accessible web apps, adding MCP capabilities to existing projects, or creating tool-based interfaces for AI interactions.

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

Command	Description
webmcp init	Initialize WebMCP in project
webmcp add-tool <name>	Add new tool definition
webmcp generate-types	Generate TypeScript types
webmcp example <type>	Create example project

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