Model Context Protocol D Implementation

A type-safe D language implementation of the Model Context Protocol for AI model integration

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Technologies Used

  • D Language
  • JSON-RPC
  • Protocol Design
  • Type-safe API

Model Context Protocol D Implementation

I developed a D language implementation of the Model Context Protocol (MCP), enabling D applications to provide functionality to AI language models through a standardized protocol. This project demonstrates my expertise in protocol design, type-safe programming, and creating clean, well-structured APIs.

Project Overview

The Model Context Protocol allows AI language models to access external tools and resources through a standardized interface. My implementation focuses on providing a type-safe, ergonomic API for D developers while maintaining full protocol compliance.

Key Contributions

Type-Safe Design

I designed the library with D's strong type system in mind, creating a fluent interface for schema definition that provides compile-time safety while maintaining the flexibility needed for the dynamic JSON-based protocol.

Resource System

The implementation includes a comprehensive resource system supporting static, dynamic, and template-based resources with a clean API for content generation and change notifications.

Protocol Compliance

The library fully implements the MCP specification (v2024-11-05) with support for all required features including tool registration, resource access, and the prompt system.

Technical Approach

Rather than using reflection or runtime type information, I designed the library to use compile-time interfaces and delegates, resulting in code that is both type-safe and efficient. This approach provides better error detection at compile time while maintaining the flexibility needed for the protocol.

The architecture separates concerns between:

  • Transport layer (handling raw message I/O)
  • Protocol layer (implementing JSON-RPC and MCP specifics)
  • Application layer (tools, resources, and prompts)

This separation allows for easy extension and customization while maintaining a clean, consistent API.

Challenges & Solutions

Dynamic Protocol with Static Types

Bridging the gap between D's static type system and the dynamic nature of JSON-RPC required careful API design. I solved this by creating a schema builder that provides type safety while generating the required JSON Schema specifications.

Resource Lifecycle Management

Managing resource lifecycles and change notifications required a careful approach to avoid memory leaks and ensure proper cleanup. I implemented a notification system that allows resources to signal changes while maintaining proper ownership semantics.

Protocol Evolution

Designing for protocol evolution required a forward-thinking approach to versioning and compatibility. The implementation includes version negotiation and a modular design that can adapt to protocol changes.

Visit the GitHub repository for complete documentation, examples, and source code.