Ktor 3.2.2 Help

Development mode

Ktor provides a special mode targeted for development. This mode enables the following capabilities:

  • Auto-reload for reloading application classes without restarting the server.

  • Extended information for debugging pipelines (with stack traces).

  • Extended debugging information on a response page in a case of a 5** server error.

Enable development mode

You can enable development mode in different ways: in the application configuration file, using a dedicated system property, or environment variable.

Configuration file

To enable development mode in a configuration file, set the development option to true:

ktor { development = true }
ktor: development: true

The 'io.ktor.development' system property

The io.ktor.development system property allows you to enable development mode when running your application.

To run an application in development mode using IntelliJ IDEA, pass io.ktor.development with the -D flag to VM options:

-Dio.ktor.development=true

If you run your application using a Gradle task, you can enable development mode in one of two ways:

  • Configure the ktor block in your build.gradle.kts file:

    ktor { development = true }
  • Enable development mode for a single run by passing a Gradle CLI flag:

    ./gradlew run -Pio.ktor.development=true

The 'io.ktor.development' environment variable

To enable development mode for a Native client, use the io.ktor.development environment variable.

15 July 2025