What to gitignore from the .idea folder?
The official support page should answer your question.
So in your .gitignore you might ignore the files ending with .iws, and the workspace.xml and tasks.xml files.
I just want to present a more recent alternative. There is an online tool that generates .gitignore files based on operating systems, IDEs and programming languages that you might be using.
EDIT Disclaimer: Do not copy this file, copy the file generated by the website instead, they do a good job on keeping it updated. This is just an example.
The file generated for IntelliJ contains the following
# Created by https://www.gitignore.io/api/intellij### Intellij #### Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and Webstorm# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839# User-specific stuff:.idea/workspace.xml.idea/tasks.xml.idea/dictionaries.idea/vcs.xml.idea/jsLibraryMappings.xml# Sensitive or high-churn files:.idea/dataSources.ids.idea/dataSources.xml.idea/dataSources.local.xml.idea/sqlDataSources.xml.idea/dynamic.xml.idea/uiDesigner.xml# Gradle:.idea/gradle.xml.idea/libraries# Mongo Explorer plugin:.idea/mongoSettings.xml## File-based project format:*.iws## Plugin-specific files:# IntelliJ/out/# mpeltonen/sbt-idea plugin.idea_modules/# JIRA pluginatlassian-ide-plugin.xml# Crashlytics plugin (for Android Studio and IntelliJ)com_crashlytics_export_strings.xmlcrashlytics.propertiescrashlytics-build.propertiesfabric.properties### Intellij Patch #### Comment Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-215987721# *.iml# modules.xml
https://www.gitignore.io/api/jetbrains
Created by https://www.gitignore.io/api/jetbrains
### JetBrains #### Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and Webstorm# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839# User-specific stuff:.idea/workspace.xml.idea/tasks.xml.idea/dictionaries.idea/vcs.xml.idea/jsLibraryMappings.xml# Sensitive or high-churn files:.idea/dataSources.ids.idea/dataSources.xml.idea/dataSources.local.xml.idea/sqlDataSources.xml.idea/dynamic.xml.idea/uiDesigner.xml# Gradle:.idea/gradle.xml.idea/libraries# Mongo Explorer plugin:.idea/mongoSettings.xml## File-based project format:*.iws## Plugin-specific files:# IntelliJ/out/# mpeltonen/sbt-idea plugin.idea_modules/# JIRA pluginatlassian-ide-plugin.xml# Crashlytics plugin (for Android Studio and IntelliJ)com_crashlytics_export_strings.xmlcrashlytics.propertiescrashlytics-build.propertiesfabric.properties### JetBrains Patch #### Comment Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-215987721# *.iml# modules.xml# .idea/misc.xml # *.ipr