Think of an MCP (Machine-Coded Protocol) server as a helpful assistant that lets an AI program «talk» to it. It provides a way for the AI to ask it to do things, like get data, change something, or even authorize a payment. When someone reviews one of these servers, they're essentially tracing the path from how a tool is described to the actual code that performs the task.
The big idea here is making sure that the interface – the part the AI client sees – explains exactly what the tool does. This includes clearly stating what happens if a request fails. For instance, can the AI tell the difference between asking for information and canceling something? Are all the necessary pieces of information for a request clearly spelled out? And, importantly, does the server actually enforce the rules it advertises its tools follow?
Developers often use examples like `textokit-mcp` (which uses JavaScript modules) and `dotnet-mcp-orders-server` (written in C#) to illustrate these points. In `textokit-mcp`, for example, tool descriptions are built from an upstream document. It's crucial to check how these descriptions are transformed. If some rules, like those across different fields, are left 'upstream', then it's wise to verify how those rejections work before assuming the advertised description covers everything. Publishing a set of rules for an interface is one thing; actually checking incoming requests against those rules is another.
Ultimately, a useful description tells the AI client two key things: what the tool can achieve, and what conditions must already be true for it to work. It should never hint at abilities – like access to sensitive data, permanent storage, or authority – that the server's actual code doesn't provide. The `orders` server, for example, makes it clear its data is «fictional» and only lives «in this server's memory». These are meaningful limits that prevent anyone from mistaking a demonstration for a real-world connection. It’s all about honesty and clarity for a trusted AI environment.