What belongs in an API's first version?

Begin with one request that matters to the product. Follow it from input to response: what must be validated, who can perform the action, what data changes and what the client needs back. Build that path clearly before adding a large structure around it.

Agree on a consistent way to report errors, configure the application and record useful diagnostic events. Include examples of expected requests and responses. Tests should cover meaningful behavior, especially access restrictions and failures that could leave data in an unexpected state.

Choose libraries with the maintaining team in mind. Record why a dependency is present and keep setup instructions current. A starter is useful when it removes repeated decisions while leaving the product's actual requirements easy to see.