Rider.Backend crashes with "Error: the required library hostfxr.dll could not be found"

Problem

Shortly after launching Rider an "A Critical Failure Has Occurred" window appears:

The backend.{TimeStamp}.{pid}.err log file contains this:

C:\Program Files\JetBrains\JetBrains Rider 2026.2.0.1\lib\ReSharperHost\windows-x64\Rider.Backend.exe --runtimeconfig C:\Program Files\JetBrains\JetBrains Rider 2026.2.0.1\lib\ReSharperHost\Rider.Backend.windows.runtimeconfig.json --Port=64600 --enablecpp
Error: the required library hostfxr.dll could not be found in [C:\Program Files\JetBrains\JetBrains Rider 2026.2.0.1\lib\ReSharperHost\windows-x64\dotnet\host\fxr\10.0.9]

Cause

The error says the necessary file is missing in the Rider installation folder. Why it can be missing isn't totally clear. The most likely reason (except for the file was deleted by mistake) is that something went wrong during the update or installation.

Resolution

Reinstall Rider to fix the issue.

If possible prior to reinstalling Rider, we would appreciate it if you could report the issue to us: Collect Rider logs (see How to collect Rider logs) and report the issue to us using one of these methods: [Report a bug], [Contact Support], via Help | Contact Support right from Rider. Attach the collected logs. Ensure to have the idea_updater.log file exist in the log archive.

If the issue happened after a major IDE update (e.g. from 2026.1.* to 2026.2.*), archive and share Rider logs directories from both versions. Example for windows: archive both %LOCALAPPDATA%\JetBrains\Rider2026.1\log and %LOCALAPPDATA%\JetBrains\Rider2026.2\log directories.