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.

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 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

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

15 July 2025