Demystifying MCP: Building a Custom Inspector to Uncover Protocol Mechanics

infrastructure #protocol 📝 Blog|Analyzed: Apr 9, 2026 05:46•

Published: Apr 9, 2026 04:30

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1 min read

Analysis

This is a brilliantly practical approach to understanding the underlying mechanics of the Model Context Protocol (MCP) that powers tools like Claude Desktop. By building a custom CLI tool to inspect raw JSON-RPC communication, the author beautifully bridges the gap between high-level SDKs and low-level protocol realities. It's an incredibly empowering read for developers looking to gain deep, hands-on visibility into how clients handle capability-based responsibilities.

Key Takeaways

•A custom interactive CLI tool was developed to visualize MCP server communication at the raw JSON-RPC level.
•The author discovered that MCP requires specific implementation responsibilities on the client side, going beyond just basic tool calling.
•A token benchmarking script was also created to measure approximate costs across multiple servers simultaneously.

Reference / Citation

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"I initially understood MCP simply as 'a common interface for calling tools,' but upon implementing it, it became clear that in reality, there are also implementation responsibilities for each capability on the client side."

Zenn ClaudeApr 9, 2026 04:30

* Cited for critical analysis under Article 32.

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