I'm confused about these tools - is this a decorator that you can add to your MCP server tools so that they don't pollute the context? How else would I add a "tool" for claude to use?

When you make API calls to generate chat completions, you specify a list of tools. They can be MCP tools, or just arbitrary tool metadata.

The API will then respond when it needs the client code to compute a tool output.

got it, thanks!