Category Archives: Swashbuckle

Swashbuckle and the Swagger UI : Curious Case of the Invalid Data Types

Swashbuckle is a nice Nuget Package that allows for easy integration with Swagger and is qualified as  one of the defacto REST API discovery tools. This along side ASP.Net’s Web Api HELP page which can showcase a service quite nicely.

One of the falicies that I have come to observe in the swashbuckle rendition is that when you generate a sample from the REST API in what is call the Swagger UI at times you have a mismatch on the data types. Now Swagger can generate a document which is JSON with the /document/v1 payload and this is not affected as you will see in the example. However, to bypass the data type issue I had to add my own rendition of the index.html for the Swagger.UI and augment some Javascript. 

Here is the issue at hand with a tutorial on how to replicate and a nice discovery on how differnt data types are rendered.

First and foremost , we set the stage.

From Visual Studio create a new Web Application.

Select Web Api and follow the screenshot for other indicators.

The following is generated.


Add a class with various data types. Types that are not common through all platforms should be utilised. Nullables of double and decimal come to mind.

Add the NuGet Package for Swashbuckle

Oversee the changes

Notice the addition of this file. We can add a maptype<> in here to tell swashbuckle what to do with a double and how to convert it but it has no effect on the Swagger.UI part. Only the JSON from /documents/v1 as an example.

Fire up the service and oversee what you get with the default tooling.

Select the API which returns your class

Notice the json the douvles have a (.) DOT and so do the decimal types.

  "datetimeVal": "2017-05-10T15:08:06.1547306-04:00",
  "stringVal": "sample string 2",
  "integerVal": 3,
  "nullIntVal": 1,
  "doubleVal": 4.1,
  "nullDoubleVal": 1.1,
  "decimalVal": 5.0,
  "nullDecimalVal": 1.0

Now fire up swagger with /swagger



 Observe what is generated, notice no (.) DOT

Copy and Paste that into a classic client generator.

Also do a Java implementation as well, same issue

The docs/v1 is ok however!

The data types are format double and type number which is what we want. 


This said careful when generating client classes as this will have casting repercussions. 

Happy Coding!