diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/AbstractHLInspection.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/AbstractHLInspection.kt
index 522eabb46c7..8523de2ce30 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/AbstractHLInspection.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/AbstractHLInspection.kt
@@ -84,6 +84,7 @@ abstract class AbstractHLInspection<PSI : KtElement, INPUT : HLApplicatorInput>(
         }
     }
 
+
     abstract val presentation: HLPresentation<PSI>
     abstract val applicabilityRange: HLApplicabilityRange<PSI>
     abstract val inputProvider: HLApplicatorInputProvider<PSI, INPUT>
@@ -96,7 +97,6 @@ private fun <PSI : PsiElement, INPUT : HLApplicatorInput> HLApplicator<PSI, INPU
 ): LocalQuickFix = object : LocalQuickFix {
     override fun startInWriteAction() = false
 
-    @OptIn(HackToForceAllowRunningAnalyzeOnEDT::class)
     override fun applyFix(project: Project, descriptor: ProblemDescriptor) {
         @Suppress("UNCHECKED_CAST")
         val element = descriptor.psiElement as PSI
diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicator.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicator.kt
index 0aae6c28bce..66b62a51a9d 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicator.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicator.kt
@@ -13,19 +13,45 @@ import org.jetbrains.kotlin.idea.frontend.api.ForbidKtResolve
 import kotlin.experimental.ExperimentalTypeInference
 import kotlin.reflect.KClass
 
+/**
+ * Applies a fix to the PSI, used as intention/inspection/quickfix action
+ * Also, knows if a fix is applicable by [isApplicableByPsi]
+ *
+ * Uses some additional information from [INPUT] to apply the element
+ */
 sealed class HLApplicator<in PSI : PsiElement, in INPUT : HLApplicatorInput> {
+
+    /**
+     * Applies some fix to given [psi], can not use resolve, so all needed data should be precalculated and stored in [input]
+     *
+     * @param psi a [PsiElement] to apply fix to
+     * @param input additional data needed to apply the fix, the [input] can be collected by [HLApplicatorInputProvider
+     */
     fun applyTo(psi: PSI, input: INPUT, project: Project?, editor: Editor?) = ForbidKtResolve.forbidResolveIn("HLApplicator.applyTo") {
         applyToImpl(psi, input, project, editor)
     }
 
+    /**
+     * Checks if applicator is applicable to specific element, can not use resolve inside
+     */
     fun isApplicableByPsi(psi: PSI): Boolean = ForbidKtResolve.forbidResolveIn("HLApplicator.isApplicableByPsi") {
         isApplicableByPsiImpl(psi)
     }
 
+    /**
+     * Action name which will be as text in inspections/intentions
+     *
+     * @see com.intellij.codeInsight.intention.IntentionAction.getText
+     */
     fun getActionName(psi: PSI, input: INPUT): String = ForbidKtResolve.forbidResolveIn("HLApplicator.getActionName") {
         getActionNameImpl(psi, input)
     }
 
+    /**
+     * Family name which will be used in inspections/intentions
+     *
+     * @see com.intellij.codeInsight.intention.IntentionAction.getFamilyName
+     */
     fun getFamilyName(): String = ForbidKtResolve.forbidResolveIn("HLApplicator.getFamilyName") {
         getFamilyNameImpl()
     }
@@ -36,6 +62,9 @@ sealed class HLApplicator<in PSI : PsiElement, in INPUT : HLApplicatorInput> {
     protected abstract fun getFamilyNameImpl(): String
 }
 
+/**
+ * Create a copy of an applicator with some components replaced
+ */
 fun <PSI : PsiElement, NEW_PSI : PSI, INPUT : HLApplicatorInput> HLApplicator<PSI, INPUT>.with(
     init: HLApplicatorBuilder<NEW_PSI, INPUT>.(olApplicator: HLApplicator<PSI, INPUT>) -> Unit
 ): HLApplicator<NEW_PSI, INPUT> = when (this@with) {
@@ -47,8 +76,12 @@ fun <PSI : PsiElement, NEW_PSI : PSI, INPUT : HLApplicatorInput> HLApplicator<PS
     }
 }
 
+/**
+ * Create a copy of an applicator with some components replaced
+ * The PSI type of a new applicator will be a class passed in [newPsiTypeTag]
+ */
 fun <PSI : PsiElement, NEW_PSI : PSI, INPUT : HLApplicatorInput> HLApplicator<PSI, INPUT>.with(
-    newPsiTypeTag: KClass<NEW_PSI>,
+    @Suppress("UNUSED_PARAMETER") newPsiTypeTag: KClass<NEW_PSI>,
     init: HLApplicatorBuilder<NEW_PSI, INPUT>.(olApplicator: HLApplicator<PSI, INPUT>) -> Unit
 ): HLApplicator<NEW_PSI, INPUT> = when (this@with) {
     is HLApplicatorImpl -> {
@@ -128,15 +161,31 @@ class HLApplicatorBuilder<PSI : PsiElement, INPUT : HLApplicatorInput> internal
 
 
     @OptIn(PrivateForInline::class)
-    fun build(): HLApplicator<PSI, INPUT> = HLApplicatorImpl(
-        applyTo = applyTo!!,
-        isApplicableByPsi = isApplicableByPsi ?: { true },
-        getActionName = getActionName ?: getFamilyName?.let { familyName -> { _, _ -> familyName.invoke() } }!!,
-        getFamilyName = getFamilyName!!
-    )
+    fun build(): HLApplicator<PSI, INPUT> {
+        val applyTo = applyTo
+            ?: error("Please, specify applyTo")
+        val getActionName = getActionName
+            ?: error("Please, specify actionName or familyName via either of: actionName,familyAndActionName")
+        val isApplicableByPsi = isApplicableByPsi ?: { true }
+        val getFamilyName = getFamilyName
+            ?: error("Please, specify or familyName via either of: familyName, familyAndActionName")
+        return HLApplicatorImpl(
+            applyTo = applyTo,
+            isApplicableByPsi = isApplicableByPsi,
+            getActionName = getActionName,
+            getFamilyName = getFamilyName
+        )
+    }
 }
 
 
+/**
+ * Builds a new applicator with HLApplicatorBuilder
+ *
+ *  Should specify at least applyTo and familyAndActionName
+ *
+ *  @see HLApplicatorBuilder
+ */
 fun <PSI : PsiElement, INPUT : HLApplicatorInput> applicator(
     init: HLApplicatorBuilder<PSI, INPUT>.() -> Unit,
 ): HLApplicator<PSI, INPUT> =
diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInput.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInput.kt
index aa7e5a954a5..2cf07c91bc7 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInput.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInput.kt
@@ -7,6 +7,20 @@ package org.jetbrains.kotlin.idea.fir.api.applicator
 
 import com.intellij.psi.PsiElement
 
+/**
+ * Data which [HLApplicator] is needed to perform the fix
+ *
+ * Created by [HLApplicatorInputProvider] or via [org.jetbrains.kotlin.idea.fir.api.fixes.HLDiagnosticFixFactory]
+ *
+ * Should not store inside
+ * - Everything that came from [org.jetbrains.kotlin.idea.frontend.api.KtAnalysisSession] like :
+ *      - [org.jetbrains.kotlin.idea.frontend.api.symbols.KtSymbol] consider using [org.jetbrains.kotlin.idea.frontend.api.symbols.pointers.KtSymbolPointer] instead
+ *      - [org.jetbrains.kotlin.idea.frontend.api.types.KtType]
+ *      - [org.jetbrains.kotlin.idea.frontend.api.calls.KtCall]
+ * - [org.jetbrains.kotlin.idea.frontend.api.KtAnalysisSession] instance itself
+ * - [PsiElement] consider using [com.intellij.psi.SmartPsiElementPointer] instead
+ *
+ */
 interface HLApplicatorInput {
     fun isValidFor(psi: PsiElement): Boolean = true
 }
diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInputProvider.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInputProvider.kt
index 199ba4463c7..9cd5cffbf74 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInputProvider.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicatorInputProvider.kt
@@ -8,7 +8,14 @@ package org.jetbrains.kotlin.idea.fir.api.applicator
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.idea.frontend.api.KtAnalysisSession
 
+/**
+ * Resolves the code to provide [HLApplicator] some input
+ */
 abstract class HLApplicatorInputProvider<PSI : PsiElement, out INPUT : HLApplicatorInput> {
+    /**
+     * Provide input to the applicator, if returns `null` then the applicator is not applicable and will not be called
+     * Guaranteed to be executed from read action, should not be called from EDT thread
+     */
     abstract fun KtAnalysisSession.provideInput(element: PSI): INPUT?
 }
 
@@ -18,6 +25,10 @@ private class HLApplicatorInputProviderImpl<PSI : PsiElement, out INPUT : HLAppl
     override fun KtAnalysisSession.provideInput(element: PSI): INPUT? = provideInput.invoke(this, element)
 }
 
+/**
+ * Creates [HLApplicatorInputProvider]
+ * The [provideInput] is guaranteed to be executed from read action, should not be called from EDT thread
+ */
 fun <PSI : PsiElement, INPUT : HLApplicatorInput> inputProvider(
     provideInput: KtAnalysisSession.(PSI) -> INPUT?
 ): HLApplicatorInputProvider<PSI, INPUT> =
diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLPresentation.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLPresentation.kt
index baa316640fd..970298d56d3 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLPresentation.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLPresentation.kt
@@ -9,7 +9,11 @@ import com.intellij.codeInspection.ProblemHighlightType
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.idea.frontend.api.ForbidKtResolve
 
-abstract class HLPresentation<PSI : PsiElement> internal constructor() {
+/**
+ * Provides a presentation to display an message in the editor which may be latter fixed by [HLApplicator]
+ * Used by [org.jetbrains.kotlin.idea.fir.api.AbstractHLInspection] to provide higlighting message and type
+ */
+sealed class HLPresentation<PSI : PsiElement> {
     fun getHighlightType(element: PSI): ProblemHighlightType = ForbidKtResolve.forbidResolveIn("HLPresentation.getHighlightType") {
         getHighlightTypeImpl(element)
     }
@@ -54,9 +58,13 @@ class HLInspectionPresentationProviderBuilder<PSI : PsiElement> internal constru
         getMessage = { text }
     }
 
-
-    internal fun build(): HLPresentation<PSI> =
-        HLPresentationImpl(getHighlightType!!, getMessage!!)
+    internal fun build(): HLPresentation<PSI> {
+        val getHighlightType = getHighlightType
+            ?: error("Please, provide highlightType")
+        val getMessage = getMessage
+            ?: error("Please, provide getMessage")
+        return HLPresentationImpl(getHighlightType, getMessage)
+    }
 }
 
 fun <PSI : PsiElement> presentation(
diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/applicators/CallableReturnTypeUpdaterApplicator.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/applicators/CallableReturnTypeUpdaterApplicator.kt
index ad447fde7af..43029164383 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/applicators/CallableReturnTypeUpdaterApplicator.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/applicators/CallableReturnTypeUpdaterApplicator.kt
@@ -20,11 +20,11 @@ import org.jetbrains.kotlin.psi.KtPsiFactory
 
 object CallableReturnTypeUpdaterApplicator {
     val applicator = applicator<KtCallableDeclaration, Type> {
-        familyName(KotlinBundle.message("fix.change.return.type.family"))
+        familyAndActionName(KotlinBundle.lazyMessage("fix.change.return.type.family"))
 
         applyTo { declaration, type, project ->
             val newTypeRef = if (!declaration.isProcedure(type)) {
-                // TODO use longTypeRepresentation and the shorten
+                // TODO use longTypeRepresentation and then shorten
                 KtPsiFactory(project ?: declaration.project).createType(type.shortTypeRepresentation)
             } else null
             runWriteAction {