The thing is, current models are good enough that you can mostly achieve the same by just putting a markdown file[1] on your server that describes their API, and tell people to point their agent at that.

For complex interactions it might be marginally more efficient to use an MCP server, but current SOTA models are good at cobbling together tools, and unless you're prepared to spend a lot of time testing how the models actually end up interacting with your MCP tools you might find it better to "just" describe your API to avoid a mismatch between what you expose and what the model thinks it needs.

[1] Slightly different, but fun: For code.claude.com, you can add ".md" to most paths and get back the docs as a Markdown file; Claude Code is aware of this, and uses it to get docs about itself. E.g. https://code.claude.com/docs/en/overview.md )