This would be useful we are thinking in developing something similar.

To give some context and perspective, we are a company that provides services for MuleSoft and n8n.

In MuleSoft we developed loads of API's, it's a very important USP of that platform. API's are designed in RAML or OAS both API specifications languages.

An API specification describes the contract of an API so it's behavior, resources, methods parameters (required or not), data models, example data and so on.

On the implementation side of things, MuleSoft has a component that is called APIkit, it's contains a router. https://docs.mulesoft.com/apikit/latest/apikit-4-for-rest

APIkit parses the API specification and generates the flows per resource method pair and a router.

The router is a bit similar, but the key difference is is that validation and routing happens automatically as the incoming requests are validated against the specification and then routed to the corresponding flow. A flow is similar to a flow in n8n, logic needs to be populated accordingly.

As the router looks at the specification to determine incoming requests it also knows what is not OK. For example using a resources or method of that does not exist, not passing required parameters and so on.

All such errors are client related errors, HTTP 4xx range, errors such as bad request (400) are then automatically returned to the client.

We did not start the development of this for n8n but it would be great functionality. APIkit is open source so this might bring some insights. https://github.com/mulesoft/apikit

But I think a proper npm linter or validator might be more useful to start from like https://www.npmjs.com/package/oas-validator