--- title: C# Tip: Mark a class as Sealed to prevent subclasses... description: Explains the sealed keyword in C# and how it prevents a class from being subclassed, contrasting it with abstract classes and method overriding via the new... canonical: https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: C# Tip: Mark a class as Sealed to prevent subclasses creation | daily.dev og:description: Explains the sealed keyword in C# and how it prevents a class from being subclassed, contrasting it with abstract classes and method overriding via the new... og:url: https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx og:image: https://api.daily.dev/og/posts/qYC4cmxHx.png og:image:alt: C# Tip: Mark a class as Sealed to prevent subclasses creation og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # C# Tip: Mark a class as Sealed to prevent subclasses creation **[Code4IT](https://daily.dev/sources/code4it)** · 4 min read · 0 upvotes · 0 comments ## Summary Explains the sealed keyword in C# and how it prevents a class from being subclassed, contrasting it with abstract classes and method overriding via the new keyword. Walks through code examples showing how sealing a class stops subclass creation at compile time, then lists three benefits: security by design (preventing unintended extension), minor performance optimizations from compiler knowledge of no subclasses, and explicit design intent communicated to other developers. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What does the sealed keyword do in C#? It prevents a class from being inherited by any subclass, causing a compile error if another class tries to extend it. This is useful when exposing classes via NuGet packages to stop consumers from altering or extending internal behavior. Benefits include security by design, minor compiler performance optimizations since no subclasses exist, and clearer communication of design intent to other developers. _daily.dev surfaces practical c# design tips like this for developers refining their class architecture._ ## Similar posts on daily.dev - [Kotlin : Sealed Classes and Interface](https://daily.dev/posts/kotlin-sealed-classes-and-interface-dtu0kurmx) · droidcon · 0 upvotes · 0 comments - [Sealed Classes in Dart: Safe, Complete switch by Design](https://daily.dev/posts/sealed-classes-in-dart-safe-complete-switch-by-design-oqklngg2m) · Medium · 0 upvotes · 0 comments - [Closed class hierarchies](https://daily.dev/posts/closed-class-hierarchies-xmmjyy63z) · .NET Escapades · 15 upvotes · 0 comments --- Tags: [#.net](https://daily.dev/tags/.net), [#c#](https://daily.dev/tags/c#) [View this post on daily.dev](https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"C# Tip: Mark a class as Sealed to prevent subclasses creation","url":"https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx"},"datePublished":"2026-10-04T13:06:53.248Z","dateModified":"2026-10-04T13:15:24.685Z","description":"Explains the sealed keyword in C# and how it prevents a class from being subclassed, contrasting it with abstract classes and method overriding via the new...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/656fb0fb0aa20bf1624174deff5a2afe?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/656fb0fb0aa20bf1624174deff5a2afe?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Code4IT","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Code4IT","logo":"https://media.daily.dev/image/upload/s--OaaG4G10--/f_auto,q_auto/v1791119049/logos/code4it?_a=BAMAMicg0","url":"https://daily.dev/sources/code4it"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":".net,c#","timeRequired":"PT4M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Code4IT","item":"https://daily.dev/sources/code4it"},{"@type":"ListItem","position":3,"name":"C# Tip: Mark a class as Sealed to prevent subclasses creation"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/c-tip-mark-a-class-as-sealed-to-prevent-subclasses-creation-qyc4cmxhx#faq","mainEntity":[{"@type":"Question","name":"What does the sealed keyword do in C#?","acceptedAnswer":{"@type":"Answer","text":"It prevents a class from being inherited by any subclass, causing a compile error if another class tries to extend it. 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