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Kotlin Inlay Hints

Kotlin Inlay Hints display computed values of string interpolations and constants directly inline in your code, making it easier to understand what your code does without having to run it.

What are Inlay Hints?

Inlay Hints are small visual annotations that appear directly in the code editor, showing additional information without modifying the source code.

The plugin adds hints for:

  • String Interpolation - Shows the computed value of interpolations
  • Constant Values - Displays resolved constant values

How They Work

String Interpolation Hints

When you have a string with interpolation, the plugin calculates and shows the resulting value:

Without Inlay Hints:

Without Inlay Hints

With Inlay Hints:

With Inlay Hints

Constant Value Hints

For constant values, the plugin resolves and shows the final value:

Inlay Hints Demo

Enabling / Disabling

Enable Hints

By default, inlay hints are enabled after installing the plugin. If you need to enable them manually:

Inlay Hints Settings

  1. Go to Settings/Preferences → Editor → Inlay Hints → Other → Kotlin
  2. Look for Kotlin Toolbox
  3. Check the options:
  4. ☑ String interpolation values
  5. ☑ Constant string values

Temporarily Disable

To temporarily disable hints without uninstalling the plugin:

  1. Access the same settings above
  2. Uncheck the desired options
  3. Hints will disappear immediately

Compatibility

K2 Mode

Fully Compatible

The plugin is fully compatible with the new Kotlin K2 compiler.

Inlay hints work perfectly in both K1 (classic) and K2 modes:

  • ✅ Kotlin K1 (Classic Compiler)
  • ✅ Kotlin K2 (New Compiler)

Kotlin Versions

Hints work with all modern versions of Kotlin:

  • ✅ Kotlin 1.9+
  • ✅ Kotlin 2.0+
  • ✅ Kotlin 2.1+

IntelliJ IDEA

Requires:

  • ✅ IntelliJ IDEA 2025.3.2 or later
  • ✅ Kotlin plugin enabled

Known Limitations

Current Limitations

Inlay hints work best with:

  • ✅ Compile-time constant values
  • ✅ String literals
  • ✅ Simple interpolations
  • ✅ Constant expressions

They do not work with:

  • ❌ Runtime-computed values
  • ❌ Results of non-const functions
  • ❌ Uninitialized mutable variables

Limitation Example

fun getUserName(): String = "Alice"

val greeting = "Hello, ${getUserName()}"
// Hint will not be shown because getUserName() is executed at runtime

Performance

Lightweight and Fast

Inlay hints are calculated asynchronously and do not impact IDE performance:

  • Do not affect typing speed
  • Do not block the interface
  • Update automatically as you edit code
  • Smart caching for optimization

Troubleshooting

Hints not showing

  1. Check that the feature is enabled:
  2. Settings → Editor → Inlay Hints → Other → Kotlin → Kotlin toolbox

  3. Make sure the options are checked

  4. Check that the code is eligible:

  5. Only constant values are supported

  6. Interpolations must be resolvable at compile time

  7. Restart the IDE if necessary

Hints are cluttering the view

  • Adjust opacity in the theme settings
  • Configure to show only on hover
  • Temporarily disable when not needed

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