Swagger: describe parameter

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JSON

swagger

So lets say I have an endpoint like this:

public async Task<IActionResult> Test([FromBody]string jsonData)

How can I provide a json schema for

jsonData

parameter? Is it possible? I know that if I have a DTO then swagger scaffolds properties from an object, but this is not what I need. My input object is a json string, not a DTO and I need to describe this json string with a valid schema. How this can be achieved?

What I have tried:

So far I have tried to generate xml documentation, but it feels wrong. Is that possible to provide description for a parameter somewhere in an endpoint comment or something alike?