Swashbuckle set manually operationId, multiple operations with same verb

EDIT This answer relates to Swashbuckle 5.6 and .NET Framework. Please read mwilson's answer for Swashbuckle and .NET Core

You can use the SwaggerOperationAttribute provided by Swashbuckle for that.

[SwaggerOperation("get")]
public IEnumerable<Contact> Get()
{
    ....
}

[SwaggerOperation("getById")]
public IEnumerable<Contact> Get(string id)
{
    ...
}

You can use that attribute to add tags and schemes to your operation as well by the way. Have a look at the source code

For swashbuckle 5.0, you can use the Name attribute. You can set it to any string but I'm a fan of using nameof like this: nameof(ActualMethodName).

[HttpGet("{id:int}", Name = nameof(GetProductById))]
public IActionResult GetProductById(int id) // operationId = "GetProductById"'

or

[HttpGet("{id:int}", Name = "GetProductById")]
public IActionResult GetProductById(int id) // operationId = "GetProductById"'

There are a few other options listed here