Extensions
Extensions are the most common way for a plugin to extend the IntelliJ Platform's functionality in a way that is not as straightforward as adding an action to a menu or toolbar.
The following are some of the most common tasks achieved using extensions:
The
com.intellij.toolWindowextension point allows plugins to add tool windows (panels displayed at the sides of the IDE user interface);The
com.intellij.applicationConfigurableextension point andcom.intellij.projectConfigurableextension point allow plugins to add pages to the Settings dialog;Custom language plugins use many extension points to extend various language support features in the IDE.
There are more than 1600 extension points available in the platform and the bundled plugins, allowing customizing different parts of the IDE behavior.
IntelliJ Community Plugins Extension Point and Listener List (bundled plugins in IntelliJ IDEA)
Lists for other IDEs are available under Product Specific (for example, PhpStorm).
Browse usages inside existing implementations of open-source IntelliJ Platform plugins via IntelliJ Platform Explorer.
Alternatively (or when using 3rd party extension points), all available extension points for the specified namespace (defaultExtensionNs) can be listed using auto-completion inside the <extensions> block in plugin.xml. Use View | Quick Documentation in the lookup list to access more information about the extension point and implementation (if applicable).
See Explore the IntelliJ Platform API for more information and strategies.
tip
Auto-completion, Quick Documentation, and other code insight features are available on extension point tags and attributes in plugin.xml.
Add an
<extensions>element to plugin.xml if it's not yet present there. Set thedefaultExtensionNsattribute to one of the following values:com.intellijif the plugin extends the IntelliJ Platform core functionality.{ID of a plugin}if the plugin extends the functionality of another plugin (must configure plugin dependencies).
Add a new child element to the
<extensions>element. The child element's name must match the name of the used extension point.Depending on the type of the extension point, do one of the following:
If the extension point was declared using the
interfaceattribute, set theimplementationattribute to the name of the class that implements the specified interface.If the extension point was declared using the
beanClassattribute, set all properties annotated with the@AttributeandTagannotations in the specified bean class.
See the Declaring Extension Point section for details.
In addition to attributes defined by the extension point, the extension element can specify basic attributes (see the attributes list in An Extension section).
Implement the extension API as required (see Implementing Extension).
To clarify this procedure, consider the following sample section of the plugin.xml file that defines two extensions designed to access the com.intellij.appStarter and com.intellij.projectTemplatesFactory extension points in the IntelliJ Platform, and one extension to access the another.plugin.myExtensionPoint extension point in another plugin another.plugin:
<!--
Declare extensions to access extension points in the IntelliJ Platform.
These extension points have been declared using "interface".
-->
<extensions defaultExtensionNs="com.intellij">
<appStarter
implementation="com.example.MyAppStarter"/>
<projectTemplatesFactory
implementation="com.example.MyProjectTemplatesFactory"/>
</extensions>
<!--
Declare extensions to access extension points in a custom plugin "another.plugin".
The "myExtensionPoint" extension point has been declared using "beanClass"
and exposes custom properties "key" and "implementationClass".
-->
<extensions defaultExtensionNs="another.plugin">
<myExtensionPoint
key="keyValue"
implementationClass="com.example.MyExtensionPointImpl"/>
</extensions>Please note the following important points:
Extension implementation must be stateless. Use explicit services for managing (runtime) data.
Avoid any initialization in the constructor, see also notes for services.
Do not perform any static initialization. Use inspection Plugin DevKit | Code | Static initialization in extension point implementations (2023.3).
An extension implementation must not be registered as a service additionally. Use inspection Plugin DevKit | Code | Extension registered as service/component (2023.3).
If an extension instance needs to "opt out" in certain scenarios, it can throw
ExtensionNotApplicableExceptionin its constructor.
When using Kotlin:
Do not use
objectbutclassfor implementation. More detailsDo not use
companion objectto avoid excessive classloading/initialization when the extension class is loaded. Use top-level declarations or objects instead. More details
Several tooling features are available to help configure bean class extension points in plugin.xml.
Properties annotated with RequiredElement are inserted automatically and validated.
If the given property is allowed to have an explicit empty value, set allowEmpty to true (2020.3+).
Property names matching the following list will resolve to a fully qualified class name:
implementationclassNameending with
Class(case-sensitive)serviceInterface/serviceImplementation
A required parent type can be specified in the extension point declaration via <with>:
<extensionPoint name="myExtension" beanClass="MyExtensionBean">
<with
attribute="psiElementClass"
implements="com.intellij.psi.PsiElement"/>
</extensionPoint>Property name language (or ending in *Language, 2020.2+) resolves to all present Language IDs.
Similarly, action and actionId (2024.3+) resolve to all registered <action> IDs.
Properties marked as @Deprecated or annotated with any of ApiStatus @Internal, @Experimental, @ScheduledForRemoval, or @Obsolete will be highlighted accordingly.
Attributes with Enum type support code insight with lowerCamelCased notation. Note: Enum implementation must not override toString().
Annotating with @Nls validates a UI String capitalization according to the text property Capitalization enum value.