Protocol Design

Before MCP, every AI tool integration was a custom build. Want ChatGPT to reach a database? Write a plugin. Want Claude to call the GitHub API? Write a Function Calling definition. Want Copilot to access your internal systems? Write a Custom Tool. Every time, the same thing: define an interface, write adapter code, handle auth, manage errors. The wheel, reinvented countless times. The problem MCP (Model Context Protocol) solves is simple: give AI agents a standard protocol for connecting tools. Just as USB-C gave electronic devices a universal connector, MCP gives AI agents a universal tool interface.

We often see URLs like these: 1 2 3 /v1/chat/completions /v1/messages /v1/responses These suffixes are not decoration — they define a complete request and response data structure. Pick the wrong one and your code either errors out or silently loses data. This article starts at /v1/completions and works its way to /v1/responses, explaining what each suffix stands for, why it was designed that way, and where the common pitfalls are.