If an app says api-ms-win-crt-runtime-l1-1-0.dll is missing, do not download that DLL from a third-party site. The file is associated with Windows’ Universal C Runtime (UCRT), a runtime dependency used by applications. On Windows 10 and 11, install available Windows updates and restart; on older Windows versions, check whether Microsoft’s specific UCRT update applies. If the error persists, follow the app publisher’s guidance for its Visual C++ runtime and installation.
What the error means
The Universal C Runtime provides C runtime functions that Windows applications may need. Microsoft says applications built with Visual Studio 2015 using the Windows 10 SDK depend on the UCRT. A missing-file message means the application cannot resolve a runtime dependency; it does not prove that this individual file was deleted. The cause may involve a Windows component that is missing or not serviced, or an app-specific installation or runtime dependency.
Microsoft describes the UCRT as an operating-system component. On Windows 10 and 11, it is serviced through Windows Update. See Microsoft’s Universal CRT deployment documentation.
Fix the error safely
1. Record your Windows and app details
Before changing anything, note your Windows version, whether it is 32-bit or 64-bit, the affected app’s name and version, and the exact error text. If an installer is needed, the runtime package’s architecture must match the application’s target architecture; do not choose solely by whether Windows itself is 32-bit or 64-bit.
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2. Update Windows 10 or 11
- Open Windows Settings and go to Windows Update. In Windows 10, this is under Update & Security; in Windows 11, it is listed in Settings.
- Check for and install available updates.
- Restart Windows, then try launching the affected app again.
Microsoft states that the UCRT is included as an operating-system component in Windows 10 and 11 and is serviced through Windows Update. Updating the operating system is the route to further UCRT servicing; see Microsoft’s UCRT deployment guidance.
3. Check the legacy UCRT update for older Windows
For older systems, Microsoft’s update KB2999226 lists Windows Server 2012 R2, Windows 8.1, Windows RT 8.1, Windows Server 2012, Windows 8, Windows RT, Windows Server 2008 R2 SP1, Windows 7 SP1, Windows Server 2008 SP2, and Windows Vista SP2. These are specific applicability listings, not a recommendation to install a package on a different Windows release.
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Use the Microsoft support page for Update for Universal C Runtime in Windows (KB2999226) to check the correct operating system, package route, and prerequisites before installing. The page describes older operating systems; verify their current support status and the package’s applicability to your system.
4. Follow the app publisher’s runtime instructions
If the app publisher recommends installing or repairing a Microsoft Visual C++ Redistributable, use the package and architecture specified for that app. Microsoft explains that Redistributables provide C and C++ runtime libraries, and an application may require a package at least as recent as the build tools used to create it. The error message alone does not identify the app’s required toolset or package, so consult the publisher’s instructions. Microsoft’s Visual C++ Redistributable download guidance explains supported packages and architecture.
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5. Repair or reinstall the app if the error continues
Use the publisher’s own installer or repair option to repair or reinstall the affected application. If it still will not start, contact the publisher and provide your Windows version, app version, app architecture if known, and the exact error message. Microsoft likewise directs users troubleshooting an application to its vendor for app-specific Redistributable instructions.
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Avoid unsafe DLL fixes
- Do not download a loose DLL from a third-party DLL site or copy it into a Windows system folder. The UCRT is a Windows component, and Microsoft documents centralized operating-system servicing for it.
- Do not assume the newest Visual C++ package is the right one. The required runtime version and architecture depend on the affected app.
- Use only official, signed runtime installers. Microsoft warns against Redistributable installers that were not downloaded from a Microsoft site or are not Microsoft-signed. See Microsoft’s Visual C++ Redistributable installation troubleshooting guidance.
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