diff --git a/buildSrc/src/main/kotlin/me/alllex/tbot/apigen/BotApiGenerator.kt b/buildSrc/src/main/kotlin/me/alllex/tbot/apigen/BotApiGenerator.kt
index 7159a01..549826f 100644
--- a/buildSrc/src/main/kotlin/me/alllex/tbot/apigen/BotApiGenerator.kt
+++ b/buildSrc/src/main/kotlin/me/alllex/tbot/apigen/BotApiGenerator.kt
@@ -105,55 +105,65 @@ val methodVariations = listOf(
 data class ValueType(
     val name: String,
     val backingType: String,
+    val docString: String? = null,
     val fieldPredicate: (type: BotApiElementName, field: BotApiElement.Field) -> Boolean
 )
 
 val valueTypes = listOf(
-    ValueType("ChatId", "Long") { type, field ->
+    ValueType("ChatId", "Long", "Chat identifier.") { type, field ->
         (type.value == "Chat" && field.serialName == "id") || field.serialName.endsWith("chat_id")
     },
-    ValueType("UserId", "Long") { type, field ->
+    ValueType("UserId", "Long", "User identifier.") { type, field ->
         (type.value == "User" && field.serialName == "id") || field.serialName.endsWith("user_id")
     },
-    ValueType("MessageId", "Long") { _, field ->
+    ValueType("MessageId", "Long", "Opaque message identifier.") { _, field ->
         !field.serialName.endsWith("inline_message_id") && field.serialName.endsWith("message_id")
     },
-    ValueType("InlineMessageId", "String") { _, field ->
+    ValueType("InlineMessageId", "String", "Opaque inline message identifier.") { _, field ->
         field.serialName.endsWith("inline_message_id")
     },
-    ValueType("MessageThreadId", "Long") { _, field ->
+    ValueType("MessageThreadId", "Long", "Opaque message thread identifier.") { _, field ->
         field.serialName.endsWith("message_thread_id")
     },
-    ValueType("CallbackQueryId", "String") { type, field ->
+    ValueType("CallbackQueryId", "String", "Opaque [CallbackQuery] identifier.") { type, field ->
         (type.value == "CallbackQuery" && field.serialName == "id") || field.serialName.endsWith("callback_query_id")
     },
-    ValueType("InlineQueryId", "String") { type, field ->
+    ValueType("InlineQueryId", "String", "Opaque [InlineQuery] identifier.") { type, field ->
         (type.value == "InlineQuery" && field.serialName == "id") || field.serialName.endsWith("inline_query_id")
     },
-    ValueType("InlineQueryResultId", "String") { type, field ->
+    ValueType("InlineQueryResultId", "String", "Opaque [InlineQueryResult] identifier.") { type, field ->
         (type.value.startsWith("InlineQuery") && field.serialName == "id") ||
             (type.value == "ChosenInlineResult" && field.serialName == "result_id")
     },
-    ValueType("FileId", "String") { _, field ->
+    ValueType("FileId", "String", "Identifier for a file, which can be used to download or reuse the file.") { _, field ->
         field.serialName.endsWith("file_id")
     },
-    ValueType("FileUniqueId", "String") { _, field ->
+    ValueType(
+        "FileUniqueId",
+        "String",
+        "Unique identifier for a file, which is supposed to be the same over time and for different bots.\n\nIt can't be used to download or reuse the file."
+    ) { _, field ->
         field.serialName.endsWith("file_unique_id")
     },
-    ValueType("ShippingQueryId", "String") { type, field ->
+    ValueType("ShippingQueryId", "String", "Opaque [ShippingQuery] identifier.") { type, field ->
         (type.value == "ShippingQuery" && field.serialName == "id") || field.serialName.endsWith("shipping_query_id")
     },
-    ValueType("WebAppQueryId", "String") { _, field ->
+    ValueType("WebAppQueryId", "String", "Opaque web-app query identifier.") { _, field ->
         field.serialName.endsWith("web_app_query_id")
     },
-    ValueType("CustomEmojiId", "String") { _, field ->
+    ValueType("CustomEmojiId", "String", "Opaque custom emoji identifier.") { _, field ->
         field.serialName.endsWith("custom_emoji_id")
     },
-    ValueType("Seconds", "Long") { _, field ->
+    ValueType("Seconds", "Long", "Duration in seconds.") { _, field ->
         field.serialName in setOf("cache_time", "duration", "life_period", "open_period", "timeout", "retry_after")
     },
-    ValueType("UnixTimestamp", "Long") { _, field ->
+    ValueType(
+        "UnixTimestamp",
+        "Long",
+        "Unix time - **number of seconds** that have elapsed since 00:00:00 UTC on 1 January 1970.",
+    ) { _, field ->
         field.serialName in setOf(
+            "date",
             "last_error_date",
             "last_synchronization_error_date",
             "emoji_status_expiration_date",
@@ -698,6 +708,13 @@ class BotApiGenerator {
     }
 
     private fun generateValueTypeSourceCode(valueType: ValueType): String = buildString {
+        valueType.docString?.let {
+            appendLine("/**")
+            it.lines().forEach { line ->
+                appendLine(" * $line")
+            }
+            appendLine(" */")
+        }
         appendLine("@Serializable")
         appendLine("@JvmInline")
         appendLine("value class ${valueType.name}(val value: ${valueType.backingType}) {")
diff --git a/src/main/generated-kotlin/me/alllex/tbot/api/model/Types.kt b/src/main/generated-kotlin/me/alllex/tbot/api/model/Types.kt
index 3727382..c45c68d 100644
--- a/src/main/generated-kotlin/me/alllex/tbot/api/model/Types.kt
+++ b/src/main/generated-kotlin/me/alllex/tbot/api/model/Types.kt
@@ -433,7 +433,7 @@ data class Chat(
 @Serializable
 data class Message(
     val messageId: MessageId,
-    val date: Long,
+    val date: UnixTimestamp,
     val chat: Chat,
     val messageThreadId: MessageThreadId? = null,
     val from: User? = null,
@@ -1546,7 +1546,7 @@ data class ChatMemberBanned(
 data class ChatMemberUpdated(
     val chat: Chat,
     val from: User,
-    val date: Long,
+    val date: UnixTimestamp,
     val oldChatMember: ChatMember,
     val newChatMember: ChatMember,
     val inviteLink: ChatInviteLink? = null,
@@ -1569,7 +1569,7 @@ data class ChatJoinRequest(
     val chat: Chat,
     val from: User,
     val userChatId: ChatId,
-    val date: Long,
+    val date: UnixTimestamp,
     val bio: String? = null,
     val inviteLink: ChatInviteLink? = null,
 ) {
@@ -3353,90 +3353,137 @@ object ReplyMarkupSerializer : JsonContentPolymorphicSerializer<ReplyMarkup>(Rep
     }
 }
 
+/**
+ * Chat identifier.
+ */
 @Serializable
 @JvmInline
 value class ChatId(val value: Long) {
     override fun toString(): String = "ChatId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * User identifier.
+ */
 @Serializable
 @JvmInline
 value class UserId(val value: Long) {
     override fun toString(): String = "UserId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque message identifier.
+ */
 @Serializable
 @JvmInline
 value class MessageId(val value: Long) {
     override fun toString(): String = "MessageId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque inline message identifier.
+ */
 @Serializable
 @JvmInline
 value class InlineMessageId(val value: String) {
     override fun toString(): String = "InlineMessageId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque message thread identifier.
+ */
 @Serializable
 @JvmInline
 value class MessageThreadId(val value: Long) {
     override fun toString(): String = "MessageThreadId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque [CallbackQuery] identifier.
+ */
 @Serializable
 @JvmInline
 value class CallbackQueryId(val value: String) {
     override fun toString(): String = "CallbackQueryId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque [InlineQuery] identifier.
+ */
 @Serializable
 @JvmInline
 value class InlineQueryId(val value: String) {
     override fun toString(): String = "InlineQueryId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque [InlineQueryResult] identifier.
+ */
 @Serializable
 @JvmInline
 value class InlineQueryResultId(val value: String) {
     override fun toString(): String = "InlineQueryResultId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Identifier for a file, which can be used to download or reuse the file.
+ */
 @Serializable
 @JvmInline
 value class FileId(val value: String) {
     override fun toString(): String = "FileId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Unique identifier for a file, which is supposed to be the same over time and for different bots.
+ * 
+ * It can't be used to download or reuse the file.
+ */
 @Serializable
 @JvmInline
 value class FileUniqueId(val value: String) {
     override fun toString(): String = "FileUniqueId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque [ShippingQuery] identifier.
+ */
 @Serializable
 @JvmInline
 value class ShippingQueryId(val value: String) {
     override fun toString(): String = "ShippingQueryId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque web-app query identifier.
+ */
 @Serializable
 @JvmInline
 value class WebAppQueryId(val value: String) {
     override fun toString(): String = "WebAppQueryId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Opaque custom emoji identifier.
+ */
 @Serializable
 @JvmInline
 value class CustomEmojiId(val value: String) {
     override fun toString(): String = "CustomEmojiId(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Duration in seconds.
+ */
 @Serializable
 @JvmInline
 value class Seconds(val value: Long) {
     override fun toString(): String = "Seconds(${quoteWhenWhitespace(value)})"
 }
 
+/**
+ * Unix time - **number of seconds** that have elapsed since 00:00:00 UTC on 1 January 1970.
+ */
 @Serializable
 @JvmInline
 value class UnixTimestamp(val value: Long) {
diff --git a/src/main/kotlin/me/alllex/tbot/api/model/Helpers.kt b/src/main/kotlin/me/alllex/tbot/api/model/Helpers.kt
index c5b3c7c..6ac97b1 100644
--- a/src/main/kotlin/me/alllex/tbot/api/model/Helpers.kt
+++ b/src/main/kotlin/me/alllex/tbot/api/model/Helpers.kt
@@ -1,6 +1,7 @@
 package me.alllex.tbot.api.model
 
 import me.alllex.tbot.api.client.TelegramBotApiClient
+import java.time.Instant
 import kotlin.time.Duration
 
 
@@ -12,6 +13,8 @@ val Duration.asSeconds get() = Seconds(this.inWholeSeconds)
 
 val User.usernameOrId: String get() = "@" + (username ?: id.value.toString())
 
+fun UnixTimestamp.toInstant(): Instant = Instant.ofEpochMilli(value * 1000)
+
 val MessageEntity.isBotCommand get(): Boolean = type == "bot_command"
 
 fun Message.findLeadCommand(): MessageEntity? {
diff --git a/version.txt b/version.txt
index 9e11b32..10145c2 100644
--- a/version.txt
+++ b/version.txt
@@ -1 +1 @@
-0.3.1
+0.4.0-SNAPSHOT