Intellij Plugin

IntelliJ Plugin Skill

Develop plugins for any IntelliJ Platform–based IDE with Kotlin, the IntelliJ Platform Gradle Plugin 2.x, and plugin.xml — from scaffolding through publishing to the JetBrains Marketplace.

> Use Kotlin. The IntelliJ Platform itself is written mostly in Kotlin, all new APIs target Kotlin first, and Java-only development is no longer supported. Target JDK 21 on current platform builds.

Core Concepts

The IntelliJ Platform is an application that hosts plugins. Understanding these building blocks prevents the most common mistakes:

• Application — the running IDE process; a singleton accessible via ApplicationManager.getApplication(). Never call read/write operations on it without the right threading model.
• Project — an open workspace; multiple Projects can exist at once. Code that holds project state must be per-project, not global.
• Module — a unit within a Project (a content root, SDK, dependencies).
• Virtual File System (VFS) — the platform's in-memory mirror of the physical file system. Always go through VirtualFile/VfsUtil, never java.io.File, for files the IDE manages.
• PSI (Program Structure Interface) — the syntax-tree layer over source files. PsiFile, PsiElement, PsiClass are how you inspect and modify code. PSI is language-aware (Java, Kotlin, XML, …).
• Action — a user-invoked command (menu item, toolbar button, shortcut) extending AnAction.
• Service — a managed singleton (AppLevel, ProjectLevel, ModuleLevel) obtained via Service.getService(...) / project.getService(...). The lifecycle and threading rules are handled for you — prefer services over hand-rolled singletons.
• Extension Point (EP) — the platform's pluggability mechanism. Plugins contribute extensions to platform-defined EPs (`) or declare their own (`) for other plugins to implement.

Quick Start

Build a plugin in five steps. Detailed keys/tasks live in [projectsetup.md](references/projectsetup.md).

1. Scaffold the project

Generate a project from the JetBrains Platform Plugin Template or the new-project wizard in IntelliJ IDEA (File → New → Project → IDE Plugin). The modern build is the IntelliJ Platform Gradle Plugin 2.x (org.jetbrains.intellij.platform) — not the legacy org.jetbrains.intellij.

2. Configure gradle.properties

# identity
pluginGroup       = com.example.myplugin
pluginName        = MyPlugin
pluginVersion     = 0.1.0

# target platform range (IDE major build numbers)
pluginSinceBuild  = 243
pluginUntilBuild  = 252.*

# platform to build against
platformType      = IC            # IC=IDEA Community, IU=Ultimate, PC=PyCharm, GO=GoLand, ...
platformVersion   = 2024.3

3. Author a minimal plugin.xml

src/main/resources/META-INF/plugin.xml:

  com.example.myplugin
  My Plugin
  Example
  
  

  com.intellij.modules.platform

  
    
  

Full tag reference and how to split config files: [pluginxml.md](references/pluginxml.md).

4. Write your first Action

class HelloAction : AnAction("Say Hello") {
  override fun actionPerformed(e: AnActionEvent) {
    val project = e.project ?: return
    NotificationGroupManager.getInstance()
      .getNotificationGroup("Hello")
      .createNotification("Hello from MyPlugin!", NotificationType.INFORMATION)
      .notify(project)
  }
}

Register it in plugin.xml:

More EPs (Tool Window, Settings, Inspection, Annotator, Line Marker): [extensionsandactions.md](references/extensionsandactions.md).

5. Run it

./gradlew runIde            # launch a sandboxed IDE with the plugin loaded
./gradlew buildPlugin       # produce a distributable .zip in build/distributions
./gradlew verifyPlugin      # run the Plugin Verifier against target IDE builds
./gradlew test              # run unit/integration tests

Project Structure

my-plugin/
├── build.gradle.kts
├── settings.gradle.kts
├── gradle.properties
├── src/
│   ├── main/
│   │   ├── kotlin/
│   │   │   └── com/example/myplugin/
│   │   │       ├── HelloAction.kt
│   │   │       └── MyToolWindowFactory.kt
│   │   └── resources/
│   │       ├── META-INF/
│   │       │   ├── plugin.xml            # main descriptor
│   │       │   └── plugin-[product].xml  # optional product-specific includes
│   │       ├── icons/
│   │       │   └── toolWindow.svg        # 13x13 SVG, current theme colors
│   │       └── inspectionDescriptions/
│   │           └── MyInspection.html
│   └── test/
│       └── kotlin/com/example/myplugin/
└── build/distributions/                  # output .zip from buildPlugin

plugin.xml Essentials

| Tag | Purpose | |-----|---------| | ` | Unique, reverse-DNS plugin id; must match pluginGroup/Gradle coordinates | | | Human-readable display name | | | email, url, plus name text | | | Markdown inside CDATA; shown on Marketplace | | | Per-release notes | | | Required module (e.g. com.intellij.modules.platform, com.intellij.modules.java) or optional dependency with config-file | | | Optional; the Gradle plugin usually controls range via pluginSinceBuild/UntilBuild | | | Extensions contributed to platform/other plugins' EPs | | | EPs this plugin exposes for others | | / | Topic listener registrations | | ` | Action declarations and group placement |

Testing

Use the IntelliJ Test Framework with light fixtures — no need to boot a full IDE.

class HelloActionTest : LightPlatformTestCase() {
  fun testActionShowsNotification() {
    val action = HelloAction()
    val e = TestActionEvent.createTestEvent { null }
    action.actionPerformed(e)
    // assert on notification/PSI/fixture state
  }
}

See [testing.md](references/testing.md) for CodeInsightTestFixture setup and PSI/VFS testing patterns.

Publishing & Signing

Plugins uploaded to the JetBrains Marketplace (since the 2021.2 cycle) must be signed. The Gradle plugin handles signing if a certificate chain is provided.

• Sign a certificate chain, base64-encode it, and expose it (plus the private key) via environment variables read by build.gradle.kts.
• ./gradlew verifyPlugin checks compatibility across your declared IDE build range.
• ./gradlew publishPlugin uploads to Marketplace when publishToken is set.

Full flow and versioning rules: [publishing.md](references/publishing.md).

Best Practices

DO:

• Use Kotlin and target JDK 21 for current builds.
• Use the IntelliJ Platform Gradle Plugin 2.x (org.jetbrains.intellij.platform), not the legacy plugin.
• Keep pluginUntilBuild open-ended (252.*) unless you have tested compatibility boundaries.
• Interact with files through VirtualFile/VFS and code through PSI, never raw java.io.File.
• Use platform services for singletons; respect read/write-access threading rules.
• Register features via extension points rather than patching platform internals.
• Run verifyPlugin against the oldest build in your sinceBuild range before release.
• Provide 13×13 SVG icons using current-theme icon colors (ColorPallete, IconLoader).

DON'T:

• Reference internal/@ApiStatus.Internal APIs from the platform — they break without warning.
• Do heavy work on the EDT (Event Dispatch Thread); offload to background via ProgressManager / coroutines on a BGT.
• Hold long-lived references to Project/PsiElement in app-level state (causes leaks and stale data).
• Ship an unsigned plugin to Marketplace (it will be rejected).
• Hardcode absolute file paths — always resolve via VirtualFile and the project's base dir.
• Pin a single platformVersion older than what your pluginSinceBuild implies.

Common Issues

| Issue | Solution | |-------|----------| | ClassNotFoundException / NoClassDefFoundError at runtime | A referenced class lives in a module you didn't ` on, or you used an @Internal API | | Plugin not loaded in sandbox | Rebuild (./gradlew runIde) and check idea.log in the sandbox instance | | verifyPlugin reports API breakages | Bump pluginSinceBuild or guard the call with com.intellij.openapi.util.SystemInfo/API checks | | Notifications don't show | Register a extension; use NotificationGroupManager | | Threading exception ("Access is allowed from event dispatch thread only") | Wrap PSI/file writes in WriteCommandAction.runWriteCommandAction; reads in a read action | | Stale PSI after edit | Call PsiDocumentManager.getInstance(project).commitDocument(doc)` before reading | | Signing fails on upload | Ensure cert chain + private key env vars are set and base64-encoded |

Knowledge References

• IntelliJ Platform SDK: official documentation at plugins.jetbrains.com/docs/intellij
• IntelliJ Platform Gradle Plugin 2.x: build system (org.jetbrains.intellij.platform)
• Kotlin: primary plugin language (JDK 21 baseline on current builds)
• PSI: program structure inspection and modification
• JetBrains Marketplace: distribution and signing

References

• [projectsetup.md](references/projectsetup.md) — Gradle plugin 2.x setup, full gradle.properties keys, build.gradle.kts template, IDE version matrix, build/run tasks
• [pluginxml.md](references/pluginxml.md) — complete plugin.xml descriptor, depends/config-file, extensions/extensionPoints, listeners, actions, config splitting
• [extensionsandactions.md](references/extensionsandactions.md) — implementing common EPs with Kotlin: Action, Tool Window, Settings, Inspection, Annotator, Line Marker, Notification
• [testing.md](references/testing.md) — IntelliJ Test Framework, CodeInsightTestFixture, light test cases, manual runIde testing
• [publishing.md](references/publishing.md) — JetBrains Marketplace, plugin signing, publishPlugin/verifyPlugin, versioning & compatibility

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: duckyman-ai
• Source: duckyman-ai/agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.