A Comprehensive Guide to Pretty Logging using Ktor in Android

Photo by Fabian Møller on Unsplash

When working with API requests in Android, logging formatted, readable JSON responses makes debugging much easier. In this blog, we’ll explore how you can pretty-print API requests and responses using Ktor.

Steps To Follow

1. Add Dependencies

Ensure your build.gradle.kts has the necessary dependencies:

dependencies {
    implementation("io.ktor:ktor-client-core:2.3.5")
    implementation("io.ktor:ktor-client-okhttp:2.3.5") // OkHttp for better logging
    implementation("io.ktor:ktor-client-logging:2.3.5") // Ktor logging
    implementation("com.squareup.okhttp3:logging-interceptor:5.0.0-alpha.11") // OkHttp logging
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.5.0") // JSON serialization
}

2. Enable Pretty Logging in Ktor

Custom Logger for Pretty JSON

Ktor’s Logging plugin does not format JSON by default. We can intercept logs and format JSON manually:

import android.util.Log
import io.ktor.client.*
import io.ktor.client.engine.okhttp.*
import io.ktor.client.plugins.logging.*
import io.ktor.client.request.*
import org.json.JSONArray
import org.json.JSONObject

// Pretty Print JSON Function
fun prettyJson(json: String): String {
    return try {
        when {
            json.startsWith("{") -> JSONObject(json).toString(4) // Format JSON Object
            json.startsWith("[") -> JSONArray(json).toString(4) // Format JSON Array
            else -> json
        }
    } catch (e: Exception) {
        json // Return as is if formatting fails
    }
}
// Custom Logger
object PrettyLogger : Logger {
    override fun log(message: String) {
        if (message.startsWith("{") || message.startsWith("[")) {
            Log.d("KtorLogger", prettyJson(message)) // Pretty JSON
        } else {
            Log.d("KtorLogger", message) // Regular log
        }
    }
}
// Create Ktor Client with Pretty Logging
val client = HttpClient(OkHttp) {
    install(Logging) {
        logger = PrettyLogger
        level = LogLevel.ALL // Log everything
    }
}
// Make a Request
suspend fun makeApiRequest() {
    val response = client.get("https://jsonplaceholder.typicode.com/posts/1").body<String>()
    Log.d("API_RESPONSE", prettyJson(response)) // Log formatted JSON
}

How This Works

✔ Logs URL, Headers, Body, and Responses ✔ Automatically formats JSON for readability ✔ Uses Logcat (Log.d) for easy debugging in Android Studio

Example Output in Logcat

When making an API request, the Logcat output looks like this:

D/KtorLogger: URL: https://jsonplaceholder.typicode.com/posts/1
D/KtorLogger: METHOD: GET
D/KtorLogger: HEADERS: Accept: application/json
D/KtorLogger: BODY:
{
    "userId": 1,
    "id": 1,
    "title": "Sample Post",
    "body": "This is a sample response body."
}

This is much easier to read than a single-line, unformatted JSON string.

Key Takeaways

✅ Use Ktor’s Logging plugin with a custom PrettyLogger for neat logs ✅ OkHttp’s LoggingInterceptor is powerful for native OkHttp clients ✅ Always log in DEBUG mode and disable logging in production!