Why Doesn't Swagger UI Display Enum Dropdown for Query Parameters?

Apr 27, 2026

Problem

When I configure allowableValues in my Swagger annotations, I expect Swagger UI to show a dropdown list of allowed values. But instead, I get only a plain text input field with no indication of valid options.

Here’s what I see in Swagger UI:

poi_types: [text input field - no dropdown]

But my swagger.json clearly has the enum values:

{
    "name": "poi_types",
    "in": "query",
    "description": "Types of locations to include",
    "required": false,
    "type": "string",
    "enum": ["pos", "wifi", "country"]
}

Environment

Spring Boot with JAX-RS
Maven project
swagger-core 1.5.20 (also tested with 1.6.2)
Swagger annotations (@ApiImplicitParam, @ApiParam)
Tested in Firefox and Chrome

What happened?

I wanted to restrict a query parameter to specific values and have Swagger UI display these as selectable options. I added allowableValues to my annotation:

@GET
@Path("/locations")
@ApiOperation("Get locations by type")
@ApiImplicitParams({
    @ApiImplicitParam(
        name = "poi_types",
        value = "Types of locations to include",
        allowableValues = "pos, wifi, country",
        dataType = "string",
        paramType = "query"
    )
})
public Response getLocations(@QueryParam("poi_types") String poiTypes) {
    // implementation
}

I verified that swagger.json was generated correctly with the enum array. But when I opened Swagger UI, I saw a plain text input field instead of a dropdown.

I tried upgrading swagger-core from 1.5.20 to 1.6.2 - no change.

I also tried using @ApiParam instead of @ApiImplicitParam:

@GET
@Path("/countries")
public Response getCountries(
    @QueryParam("isocc2")
    @ApiParam(
        name = "isocc2",
        value = "Country code",
        allowableValues = "en, es"
    )
    String countryCode) {
    // implementation
}

Same result - enum in swagger.json, but no dropdown in Swagger UI.

Why this happens?

I think there are several potential causes:

Swagger UI version mismatch - The swagger-core library version controls spec generation, but Swagger UI is a separate component. Spring Boot may bundle an older UI version that doesn’t properly render enums for query parameters.
OpenAPI 2.0 vs 3.0 format - Swagger 2.0 (OpenAPI 2.0) uses a different parameter structure than OpenAPI 3.0:

"name": "status",
"in": "query",
"type": "string",
"enum": ["active", "inactive", "pending"]

"name": "status",
"in": "query",
"schema": {
    "type": "string",
    "enum": ["active", "inactive", "pending"]
}

Newer Swagger UI versions (3.x+) may expect the OpenAPI 3.0 format with the schema wrapper.

Browser caching - The browser might cache an older swagger.json or UI assets.

How to diagnose it?

I recommend checking these things:

Verify Swagger UI version - Open browser dev tools and look for the version in loaded JavaScript or HTML footer.
Check swagger.json loading - Use the Network tab in dev tools to confirm the correct swagger.json is being loaded.
Clear browser cache - Hard refresh with Ctrl+Shift+R (or Cmd+Shift+R on Mac).
Test standalone Swagger UI - Try serving your swagger.json to a standalone swagger-ui-dist instance to compare rendering.
Check framework integration - Spring Boot swagger starters may bundle specific UI versions.

What can you try?

If swagger.json is correct but UI doesn’t render dropdowns:

Upgrade Swagger UI separately - Don’t assume upgrading swagger-core affects the UI.
Consider OpenAPI 3.0 migration - Use springdoc-openapi instead of older swagger libraries for better UI compatibility.
Use standalone Swagger UI - Download swagger-ui-dist and serve your swagger.json directly.

Summary

In this post, I explained why Swagger UI may not display enum dropdowns even with correct swagger.json. The key point is that swagger-core and Swagger UI are separate - upgrading swagger-core doesn’t upgrade the UI. Check your actual Swagger UI version, consider OpenAPI 3.0 migration, and test with standalone UI to isolate the issue.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

👨‍💻 Stack Overflow: Swagger UI doesn't render allowableValues

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!