IntelliJ IDEA Cannot Run or Compile the Project

How to fix it

Try these in order — the most common fix is first.

1. 1. Open as a build project

   1. Use File | Open and select pom.xml or build.gradle, then choose Open as Project
   Did this fix it? Yes No

2. 2. Check SDK and source roots

   1. See File | Project Structure and mark source roots as needed
   Did this fix it? Yes No

3. 3. Rebuild

   1. Use Build | Rebuild Project
   Did this fix it? Yes No

4. 4. Invalidate caches

   1. File | Invalidate Caches, then Invalidate and Restart
   Did this fix it? Yes No

Symptoms

Run button disabled, 'No main class found', build errors that do not occur in the terminal.

Why it happens

• Project opened as plain folder instead of via pom.xml/build.gradle
• No SDK or output path
• Source root not marked
• Stale build output

This guide also covers

• intellij cannot run project
• intellij run button greyed out
• intellij no main class found

Other JetBrains IntelliJ errors

• IntelliJ IDEA Indexing Takes Forever
• IntelliJ IDEA High Memory Usage
• IntelliJ IDEA Slow or Freezing
• IntelliJ IDEA Cannot Resolve Symbol
• IntelliJ IDEA Maven Import Failed
• IntelliJ IDEA Gradle Sync Failed
• IntelliJ IDEA JDK Not Found or Invalid
• IntelliJ IDEA License or Activation Error