If you look at the actual raw output of tools/list call you may find it surprisingly similar to the OpenAPI spec for the same interface. In fact they are trivially convertible to each other.
Personally I find OpenAPI spec being more practical since it includes not just endpoints with params, but also outputs and authentication.
Know all that from my own experience plugging dozens of APIs to both MCP/Claude and ChatGPT.
Look at https://knoema.com which positions itself as a search engine for data with more than 2.5 billion time series available. They provide both visual data discovery through search and navigation as well as API access through Python, R etc.
Personally I find OpenAPI spec being more practical since it includes not just endpoints with params, but also outputs and authentication.
Know all that from my own experience plugging dozens of APIs to both MCP/Claude and ChatGPT.