MCP WASM Server

Overview

The WASM MCP Server is a lightweight proof‑of‑concept that brings the Model Context Protocol into the browser by running an MCP server inside WebAssembly. It demonstrates how AI assistants can interact with tools and resources that are natively available in a web page, without requiring a backend server or network calls. By compiling the MCP logic to WASM, developers can embed a fully‑functional assistant backend directly into client‑side applications, enabling offline or low‑latency interactions.

Problem Solved

Traditional MCP servers run on a Node.js process or other server‑side runtime, which can be overkill for simple web demos or low‑resource environments. The WASM implementation removes that dependency, allowing developers to prototype MCP integrations entirely in the browser. This solves the challenge of “how do I test or showcase MCP tools without spinning up a server?” and opens the door to client‑side AI assistants that can run offline or in restricted network conditions.

Core Functionality

The server exposes two concrete tools and a resource system:

• Calculator Tool – Performs basic arithmetic (add, subtract, multiply, divide) with real‑time validation and error handling. It demonstrates tool registration, schema validation via Zod, and synchronous execution.
• Storage System – A key‑value store that persists for the duration of a browser session. It shows how resources can be parameterized () and accessed through read callbacks, illustrating the resource model of MCP.
• Template‑Based Resources – The storage keys are embedded into template paths, allowing the assistant to reference stored data by URL and letting the server resolve those URLs at runtime.

The server’s architecture uses a custom browser transport layer to shuttle messages between the MCP client (e.g., Claude) and the WASM module, keeping the communication loop entirely within the browser.

Key Features Explained

• Tool Registration – Tools are added with , each bound to a callback that receives validated input and returns output or errors.
• Schema Validation – Input schemas are defined with Zod, ensuring that only correctly structured data reaches the tool logic.
• Resource Templates – Paths like allow dynamic lookup of stored values, showcasing how MCP resources can be accessed via URLs.
• Error Handling – The server gracefully reports initialization, execution, and transport errors back to the client, mirroring real‑world MCP error flows.
• WebAssembly Execution – All logic runs in a WASM module, providing near‑native performance and isolation from the host page.

Use Cases & Real‑World Scenarios

• Browser‑Based AI Assistants – Embed an assistant in a web app that can perform calculations or retrieve user‑saved data without server roundtrips.
• Offline Prototyping – Test MCP tool interactions locally during development, reducing latency and simplifying CI pipelines.
• Educational Demos – Show students how MCP works by running a complete server in the browser, making concepts tangible.
• Security‑Sensitive Environments – Keep all data on the client side, useful for privacy‑focused applications where backend storage is undesirable.

Integration with AI Workflows

An MCP client can connect to this server using the standard MCP transport protocol. The assistant’s prompt can reference the calculator tool or a storage URL, and the client will dispatch those requests to the WASM server. The server returns results or errors immediately, allowing the assistant to incorporate them into its response generation loop. Because the server runs in the same process as the client, latency is minimal and the integration feels seamless.

Unique Advantages

• Zero Server Dependency – Eliminates the need for a Node.js process or external API, simplifying deployment.
• Offline Capability – All operations occur locally; the assistant can function without internet access after initial load.
• WASM Performance – The module runs at near‑native speed, making real‑time tool execution practical.
• Demonstration Power – Serves as a minimal, self‑contained example that developers can extend with new tools or resources without touching the host environment.

In summary, the WASM MCP Server showcases how an MCP backend can be compressed into a browser‑friendly module, enabling developers to prototype, test, and deploy AI assistants that rely on custom tools and resources—all without a traditional server infrastructure.