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Add NETSDK1242 SDK error documentation #54379

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bd5b455
Add NETSDK1242 SDK error documentation
kotlarmilos Jun 15, 2026
47596ff
Clarify NETSDK1242 applies to .NET 11 and later
kotlarmilos Jun 15, 2026
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1 change: 1 addition & 0 deletions docs/core/tools/sdk-errors/index.md
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Expand Up @@ -382,3 +382,4 @@
|[NETSDK1238](netsdk1238.md)|The current .NET SDK ({0}) has known vulnerabilities ({1}).{2} See <https://dotnet.microsoft.com/download>|
|[NETSDK1239](netsdk1239.md)|The current .NET SDK ({0}) is end of life as of {1}. It will receive no further security updates: <https://dotnet.microsoft.com/download>|
|[NETSDK1240](netsdk1240.md)|The current .NET SDK ({0}) has no newer release in its feature band. Update to version {1}: <https://dotnet.microsoft.com/download>|
|[NETSDK1242](netsdk1242.md)|Building {0} projects with the Mono runtime is not supported in .NET 11.0 and later. Use the .NET 10.0 SDK to build this project.|

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docs/core/tools/sdk-errors/index.md:385:159 MD047/single-trailing-newline Files should end with a single newline character https://github.com/DavidAnson/markdownlint/blob/v0.40.0/doc/md047.md
43 changes: 43 additions & 0 deletions docs/core/tools/sdk-errors/netsdk1242.md
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---
title: "NETSDK1242: Building projects with the Mono runtime is not supported in .NET 11 and later"
description: Learn how to resolve build error NETSDK1242, which reports that the Mono runtime is not supported for the target mobile platform in .NET 11 and later.
ms.topic: error-reference
ms.date: 06/15/2026
ai-usage: ai-assisted
f1_keywords:
- NETSDK1242
---
# NETSDK1242: Building projects with the Mono runtime is not supported in .NET 11 and later

This error indicates that the project selects the Mono runtime (the `UseMonoRuntime` property is set to `true`) for a mobile target platform while targeting .NET 11 or later, where the Mono runtime is no longer supported for that platform. The full error message is similar to the following example:

> NETSDK1242: Building ios projects with the Mono runtime is not supported in .NET 11.0 and later. Use the .NET 10.0 SDK to build this project.

The error applies to the `android`, `ios`, `maccatalyst`, and `tvos` target platforms.

## Resolve the error

Choose one of the following options:

- Build the project with the .NET 11 SDK or later without selecting the Mono runtime. Remove the `UseMonoRuntime` property from the project, or set it to `false`:

```xml
<PropertyGroup>
<UseMonoRuntime>false</UseMonoRuntime>
</PropertyGroup>
```

- If the project requires the Mono runtime, build it with the .NET 10 SDK. Add a `global.json` file at the root of the project to select that SDK version:

```json
{
"sdk": {
"version": "10.0.100"
}
}
```

## See also

- [global.json overview](../global-json.md)
- [.NET SDK error and warning reference](index.md)

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4 changes: 3 additions & 1 deletion docs/navigate/tools-diagnostics/toc.yml
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Expand Up @@ -99,6 +99,8 @@ items:
href: ../../core/tools/sdk-errors/netsdk1239.md
- name: NETSDK1240
href: ../../core/tools/sdk-errors/netsdk1240.md
- name: NETSDK1242
href: ../../core/tools/sdk-errors/netsdk1242.md
- name: BuildCheck rules
items:
- name: Index of rules
Expand Down Expand Up @@ -4241,4 +4243,4 @@ items:
- name: Compatible framework validator
href: ../../fundamentals/apicompat/package-validation/compatible-framework-validator.md
- name: Microsoft.DotNet.ApiCompat.Tool global tool
href: ../../fundamentals/apicompat/global-tool.md
href: ../../fundamentals/apicompat/global-tool.md
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