title: "Building an Open-Source MCP Server for AI Coding IDEs" date: "2026-03-15T00:00:00Z" excerpt: "How VIBETTER provides structured, source-grounded intelligence to Claude Code and Cursor using FastMCP 3.0." tag: "Open Source" readTime: "7 min" accentColor: "orange"

Giving AI True Codebase Understanding

AI coding assistants like Claude Code, Cursor, and Windsurf are fundamentally limited by the context they receive. They operate on flat text, lacking structured understanding of how files relate, what changed and why, and where specific logic lives.

To solve this, I built VIBETTER, an open-source MCP (Model Context Protocol) server designed to give AI coding assistants genuine codebase understanding.

Why FastMCP 3.0?

Standardizing on the MCP protocol ensures compatibility across modern IDEs while reducing the maintenance burden. FastMCP's tool registration pattern keeps the codebase clean and extensible. Instead of building a custom protocol that only works with one tool, VIBETTER plugs into the growing ecosystem of MCP-compatible clients natively.

# Example of FastMCP tool registration in VIBETTER
@mcp.tool()
async def get_dependency_graph(file_path: str) -> str:
    """Returns the dependency graph for a given file."""
    # Logic to build and return the graph
    pass

Source-Grounded Citations

One of the biggest issues with LLMs explaining code is hallucination. To combat this, VIBETTER enforces source-grounded citations. Every response the server provides references specific files and line numbers.

This makes outputs verifiable. If the AI claims a function does X, the developer can click the citation and verify it immediately.

Fallback Model Chaining

Production reliability requires graceful degradation. If the primary model fails or hits rate limits, the server automatically falls back to alternative models. This ensures the developer's workflow isn't interrupted by API outages.

Conclusion

MCP protocol adoption is accelerating. Building on standards pays off in ecosystem reach, and source grounding is non-negotiable for code intelligence tools — developers need to verify AI claims. VIBETTER is MIT licensed and publicly available for anyone to use and extend.