JSON Parsing in Android: Kotlinx Serialization vs. Moshi

When an Android app queries a web API, the server transmits payloads formatted as JSON (JavaScript Object Notation). To work with this data in Kotlin, the app must deserialize the raw JSON text into typed Kotlin data classes. In this class, we compare the three primary parsers: Kotlinx Serialization, Moshi, and legacy Gson.

Parser Comparison: Kotlinx Serialization vs. Moshi vs. Gson

Modern Parsing with Kotlinx.Serialization

import kotlinx.serialization.Serializable
import kotlinx.serialization.SerialName
import kotlinx.serialization.json.Json

@Serializable
data class UserDTO(
    @SerialName("user_id")
    val id: Int,

    @SerialName("full_name")
    val name: String,

    @SerialName("email_address")
    val email: String,

    @SerialName("is_vip")
    val isVip: Boolean = false // Default fallback if missing in JSON!
)

fun parseJsonExample() {
    val rawJson = """
        {
            "user_id": 404,
            "full_name": "Jordan Smith",
            "email_address": "jordan@veewom.com"
        }
    """.trimIndent()

    val jsonConfig = Json {
        ignoreUnknownKeys = true // Prevents crashes when backend adds new fields!
        coerceInputValues = true  // Coerces invalid nulls to default values
    }

    val user: UserDTO = jsonConfig.decodeFromString(rawJson)
    Log.d("ParsedUser", "User name: ${user.name}, VIP: ${user.isVip}")
}