Inlay hints render small pieces of information directly into the editor and give developers additional code insight without disturbing the workflow. A well-known example is parameter hints that usually display the name of the function parameters as given in its declaration. They are closely related to Parameter Info which shows parameter types for all possible overloads of a function but opens as a popup overlaying the code.
Inlay hints are flexible and have a wide range of applications in the IntelliJ Platform. For instance, the following are well-known examples where inlay hints are used:
Java uses inlays to display type annotations in Java chained method calls.
Kotlin uses inlays in range expressions to show, e.g. less-than, or less-than-or-equal signs to let developers know if intervals are inclusive or exclusive.
In version-controlled projects, the author of the code is shown using inlay hints.
The main characteristic of the inlay is the way it is displayed in the editor:
inline - inlays displayed in the code between code tokens
block - inlays displayed above a code block
Depending on the requirements and target IntelliJ Platform version, there are several extension points to choose from, when implementing inlay hints.
This section describes the available APIs and their use cases.
To inspect existing Inlays in the IDE, use UI Inspector. Corresponding entries from are also available from Inspecting Settings.
Inlay Parameter Hints ProviderInlay parameter hints are simple string inline inlays placed before parameter names in method and function calls. It is not possible to provide advanced presentation and behavior of inlay parameter hints.
To provide inlay parameter hints, implement InlayParameterHintsProvider and register it in com.intellij.codeInsight.parameterNameHints extension point (EP). The API documentation of InlayParameterHintsProvider explains in detail the rationale behind all methods.
Examples:
GroovyInlayParameterHintsProvider - shows parameter hints in Groovy code
KotlinInlayParameterHintsProvider - shows parameter hints in Kotlin code
To suppress inlay parameter hints in specific places, implement ParameterNameHintsSuppressor and register it in com.intellij.codeInsight.parameterNameHintsSuppressor extension point.
Declarative inlay hints are inline textual inlays that can hold expandable list of clickable items. Please note this API has limited presentation customization possibilities due to its UI-independent design, which allows utilizing it by different frontend technologies (not only in Swing).
To provide declarative inlay hints implement declarative InlayHintsProvider and register it in com.intellij.codeInsight.declarativeInlayProvider extension point. See the API documentation for the details.
Examples:
JavaImplicitTypeDeclarativeInlayHintsProvider - shows inferred type for variables declared with the var keyword in Java code when the inferred type may not be clear
JavaMethodChainsDeclarativeInlayProvider - shows method return types in call chains in Java code
To provide a custom configuration UI, implement InlayHintsCustomSettingsProvider registered in com.intellij.codeInsight.declarativeInlayProviderCustomSettingsProvider extension point.
Preview texts displayed for inlay hint providers under must be located in plugin resources in inlayProviders/$provider_id$ directory, for example, inlayProviders/java.implicit.types. The $provider_id$ value must match the providerId attribute of com.intellij.codeInsight.declarativeInlayProvider extension point. The preview file name must be preview.$ext$, where $ext$ is a default extension of a supported file type, for example, preview.java. Hints displayed in the preview panel are defined with the dedicated markup:
Examples:
Code Vision ProviderThis API is still in experimental state and may be changed without preserving backward compatibility.
Code vision provider allows for providing block inlay hints for elements like class, method, field, etc. If there are multiple hints provided for a single element, all will be displayed in the same line to save vertical space.
Code vision hints can be displayed over the element, or on the right, at the end of line. It is configurable by users in by choosing a value in Default position for metrics combo box, or by selecting Position in specific provider entries.
There are three extension points for implementing a code vision provider:
DaemonBoundCodeVisionProvider registered in com.intellij.codeInsight.daemonBoundCodeVisionProvider extension point
CodeVisionProvider registered in com.intellij.codeInsight.codeVisionProvider extension point
CodeVisionGroupSettingProvider registered in com.intellij.config.codeVisionGroupSettingProvider extension point
DaemonBoundCodeVisionProvider API should be used in cases when code vision entries are related to PSI, so that calculated values are invalidated and recalculated on PSI changes.
CodeVisionProvider API should be used for cases when presented information doesn't depend on the PSI.
The CodeVisionGroupSettingProvider is necessary for displaying the name and description of the code vision provider in the settings. The groupId must match the value specified in the implementation of the CodeVisionProvider; if not specified, it defaults to the id. The groupName is the name shown in the code vision group, and the description will be visible in the right details panel.
Code vision preview is available under . In case if multiple preview examples in different languages are provided for an existing code vision provider, IDE will choose the most important from its point of view. For example, IntelliJ IDEA will use Java preview, PhpStorm will use PHP preview, etc.
To provide a preview example for a custom code vision provider:
Create a codeVisionProviders/$model_id$/preview.$ext$ file, for example, codeVisionProviders/vcs.code.vision/preview.java. The $modelId$ must match the groupId of CodeVisionGroupSettingProvider and modelId (see 2.).
Register an com.intellij.codeInsight.codeVisionSettingsPreviewLanguage, which specifies the preview language and modelId.
Examples:
JavaInheritorsCodeVisionProvider - shows number of Java class or method inheritors. Clicking the inlay hint opens the list of inheritors. This provider is DaemonBoundCodeVisionProvider.
JavaReferencesCodeVisionProvider - shows number of usages of Java class or member. Clicking the inlay opens the list of usages or navigates to the usage if only one exists. This provider is DaemonBoundCodeVisionProvider.
VcsCodeVisionProvider - shows the author of a given element, e.g., class or method, based on VCS information. This provider is CodeVisionProvider.
Inlay hints provider allows for implementing both inline and block inlay hints with custom presentation and behavior. See the API documentation for the details.
For implementing inline inlay hints in versions 2023.1 and newer, Declarative Inlay Hints Provider is recommended.
For implementing block inlay hints in versions 2022.1 and newer, Code Vision Provider is recommended.
To provide inlay hints, implement InlayHintsProvider and register it in com.intellij.codeInsight.inlayProvider extension point. See the API documentation for the details.
Examples:
GroovyLocalVariableTypeHintsInlayProvider - shows local variable types in Groovy code
MarkdownTableInlayProvider - decorates tables in Markdown files.
For a more complex example, see KotlinLambdasHintsProvider, its parent class and all implementations.
Go to (Product Help) and check out inlays that have already been implemented.
To support multiple languages with a single type of inlay hints, see declarative InlayHintsProviderFactory (2023.1+) or InlayHintsProviderFactory (pre-2023.1).
For testing inlay hints, see InlayHintsProviderTestCase and InlayParameterHintsTest.
16 April 2025
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