# All About Opt-In Annotations

DevFeed: [All About Opt-In Annotations](<https://devfeed.tech/articles/all-about-opt-in-annotations-27075.md>)

Original publisher: [Read original article](<https://zsmb.co/opt-in-annotations/>)

Author: Márton Braun

Published: 2021-09-28T15:00:00Z

Content type: tutorial

Language: en

Sources: [zsmb.co](<https://devfeed.tech/sources/zsmb-co.md>)

Topics: [Kotlin](<https://devfeed.tech/topics/kotlin.md>), [Library](<https://devfeed.tech/topics/library.md>)

Tags: [android](<https://devfeed.tech/tags/android.md>), [article](<https://devfeed.tech/tags/article.md>), [code](<https://devfeed.tech/tags/code.md>), [compilation](<https://devfeed.tech/tags/compilation.md>), [compilation-error](<https://devfeed.tech/tags/compilation-error.md>), [guide](<https://devfeed.tech/tags/guide.md>), [how-to](<https://devfeed.tech/tags/how-to.md>), [kotlin](<https://devfeed.tech/tags/kotlin.md>), [marton-braun](<https://devfeed.tech/tags/marton-braun.md>), [visibility](<https://devfeed.tech/tags/visibility.md>), [zsmb](<https://devfeed.tech/tags/zsmb.md>), [zsmb-co](<https://devfeed.tech/tags/zsmb-co.md>), [zsmb13](<https://devfeed.tech/tags/zsmb13.md>), [zsmbco](<https://devfeed.tech/tags/zsmbco.md>)

## AI overview

A guide to Kotlin opt-in annotations, explaining how to create opt-in marker annotations, mark APIs as requiring opt-in, and use those APIs correctly. It also discusses severity levels, compilation behavior, and applications in libraries and multi-module projects.

## Source excerpt

Have you ever encountered APIs that show warnings or errors when you use them, saying that they're internal or experimental? In this guide, you'll learn everything you need to know about opt-in APIs in Kotlin: how to create and use them, and all their nuances.