Base64 in Kotlin
How to encode and decode Base64 in Kotlin — with copy-paste examples and a live converter to check your output.
On the JVM, Kotlin uses java.util.Base64 directly. Kotlin 1.8+ also ships an experimental kotlin.io.encoding.Base64 for multiplatform code.
Encode to Base64 in Kotlin
import java.util.Base64
val encoded = Base64.getEncoder().encodeToString("Hello, World!".toByteArray(Charsets.UTF_8))Decode Base64 in Kotlin
import java.util.Base64
val decoded = Base64.getDecoder().decode(encoded)
val text = String(decoded, Charsets.UTF_8)Notes & gotchas
Use Base64.getUrlEncoder() for the URL-safe alphabet. For Kotlin Multiplatform (non-JVM targets), use the experimental kotlin.io.encoding.Base64.Default / Base64.UrlSafe objects instead of java.util.Base64.
Try it live
Base64 in Kotlin — FAQ
How do I Base64 encode a string in Kotlin?+
Use the code shown above. Use Base64.getUrlEncoder() for the URL-safe alphabet. For Kotlin Multiplatform (non-JVM targets), use the experimental kotlin.io.encoding.Base64.Default / Base64.UrlSafe objects instead of java.util.Base64.
How do I decode Base64 back to text in Kotlin?+
Use the decode snippet above. Base64 decoding is lossless, so you get the exact original bytes back; decode them with UTF-8 to recover text.
Is Base64 encoding the same across programming languages?+
Yes. Base64 is a standard (RFC 4648), so a string encoded in one language decodes correctly in any other. Only the API differs, not the output.
Does Base64 secure my data?+
No. Base64 is an encoding, not encryption — anyone can decode it. Never use it to protect secrets.