diff --git a/kotlinpoet/src/commonMain/kotlin/com/squareup/kotlinpoet/CodePoint.kt b/kotlinpoet/src/commonMain/kotlin/com/squareup/kotlinpoet/CodePoint.kt
new file mode 100644
index 000000000..0479320f9
--- /dev/null
+++ b/kotlinpoet/src/commonMain/kotlin/com/squareup/kotlinpoet/CodePoint.kt
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.kotlinpoet
+
+import kotlin.jvm.JvmInline
+
+@JvmInline
+internal value class CodePoint(val code: Int)
+
+internal expect fun String.codePointAt(index: Int): CodePoint
+
+internal expect fun CodePoint.isLowerCase(): Boolean
+internal expect fun CodePoint.isUpperCase(): Boolean
+
+internal expect fun CodePoint.isJavaIdentifierStart(): Boolean
+internal expect fun CodePoint.isJavaIdentifierPart(): Boolean
+
+internal expect fun CodePoint.charCount(): Int
+
+internal expect fun StringBuilder.appendCodePoint(codePoint: CodePoint): StringBuilder
diff --git a/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/NameAllocator.kt b/kotlinpoet/src/commonMain/kotlin/com/squareup/kotlinpoet/NameAllocator.kt
similarity index 92%
rename from kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/NameAllocator.kt
rename to kotlinpoet/src/commonMain/kotlin/com/squareup/kotlinpoet/NameAllocator.kt
index a6c570b9e..73f6dd317 100644
--- a/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/NameAllocator.kt
+++ b/kotlinpoet/src/commonMain/kotlin/com/squareup/kotlinpoet/NameAllocator.kt
@@ -15,7 +15,9 @@
  */
 package com.squareup.kotlinpoet
 
-import java.util.UUID
+import kotlin.jvm.JvmOverloads
+import kotlin.random.Random
+import kotlin.random.nextULong
 
 /**
  * Assigns Kotlin identifier names to avoid collisions, keywords, and invalid characters. To use,
@@ -118,7 +120,8 @@ public class NameAllocator private constructor(
    */
   @JvmOverloads public fun newName(
     suggestion: String,
-    tag: Any = UUID.randomUUID().toString(),
+    // TODO It's possible to use `kotlin.uuid.Uuid` when it's stable
+    tag: Any = Random.nextULong().toString(16).padStart(16, '0'),
   ): String {
     var result = toJavaIdentifier(suggestion)
     while (!allocatedNames.add(result)) {
@@ -154,18 +157,18 @@ private fun toJavaIdentifier(suggestion: String) = buildString {
   while (i < suggestion.length) {
     val codePoint = suggestion.codePointAt(i)
     if (i == 0 &&
-      !Character.isJavaIdentifierStart(codePoint) &&
-      Character.isJavaIdentifierPart(codePoint)
+      !codePoint.isJavaIdentifierStart() &&
+      codePoint.isJavaIdentifierPart()
     ) {
       append("_")
     }
 
-    val validCodePoint: Int = if (Character.isJavaIdentifierPart(codePoint)) {
+    val validCodePoint: CodePoint = if (codePoint.isJavaIdentifierPart()) {
       codePoint
     } else {
-      '_'.code
+      CodePoint('_'.code)
     }
     appendCodePoint(validCodePoint)
-    i += Character.charCount(codePoint)
+    i += codePoint.charCount()
   }
 }
diff --git a/kotlinpoet/src/jsMain/kotlin/com/squareup/kotlinpoet/CodePoint.js.kt b/kotlinpoet/src/jsMain/kotlin/com/squareup/kotlinpoet/CodePoint.js.kt
new file mode 100644
index 000000000..6789369ca
--- /dev/null
+++ b/kotlinpoet/src/jsMain/kotlin/com/squareup/kotlinpoet/CodePoint.js.kt
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.kotlinpoet
+
+internal actual fun String.codePointAt(index: Int): CodePoint {
+  val code = jsCodePointAt(this, index)
+  return CodePoint(code)
+}
+
+internal actual fun CodePoint.isLowerCase(): Boolean {
+  // TODO Will there be a problem? Is there a better way?
+  val str = jsFromCodePoint(this.code)
+
+  if (str.length != 1) {
+    return false
+  }
+
+  return str.first().isLowerCase()
+}
+
+internal actual fun CodePoint.isUpperCase(): Boolean {
+  // TODO Will there be a problem? Is there a better way?
+  val str = jsFromCodePoint(this.code)
+
+  if (str.length != 1) {
+    return false
+  }
+
+  return str.first().isUpperCase()
+}
+
+@Suppress("unused")
+private fun jsCodePointAt(str: String, index: Int): Int =
+  js("str.codePointAt(index)").unsafeCast<Int>()
+
+@Suppress("unused")
+private fun jsFromCodePoint(code: Int): String =
+  js("String.fromCodePoint(code)").toString()
diff --git a/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/ClassName.kt b/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/ClassName.kt
index 5eeb21b0a..59ce4bf8e 100644
--- a/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/ClassName.kt
+++ b/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/ClassName.kt
@@ -220,7 +220,7 @@ public class ClassName internal constructor(
 
       // Add the package name, like "java.util.concurrent", or "" for no package.
       var p = 0
-      while (p < classNameString.length && Character.isLowerCase(classNameString.codePointAt(p))) {
+      while (p < classNameString.length && classNameString.codePointAt(p).isLowerCase()) {
         p = classNameString.indexOf('.', p) + 1
         require(p != 0) { "couldn't make a guess for $classNameString" }
       }
@@ -228,7 +228,7 @@ public class ClassName internal constructor(
 
       // Add the class names, like "Map" and "Entry".
       for (part in classNameString.substring(p).split('.')) {
-        require(part.isNotEmpty() && Character.isUpperCase(part.codePointAt(0))) {
+        require(part.isNotEmpty() && part.codePointAt(0).isUpperCase()) {
           "couldn't make a guess for $classNameString"
         }
 
diff --git a/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/CodePoint.jvm.kt b/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/CodePoint.jvm.kt
new file mode 100644
index 000000000..ff02a2c6e
--- /dev/null
+++ b/kotlinpoet/src/jvmMain/kotlin/com/squareup/kotlinpoet/CodePoint.jvm.kt
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.kotlinpoet
+
+import kotlin.text.codePointAt as codePointAtKt
+
+internal actual fun String.codePointAt(index: Int): CodePoint =
+  CodePoint(codePointAtKt(index))
+
+internal actual fun CodePoint.isLowerCase(): Boolean =
+  Character.isLowerCase(code)
+
+internal actual fun CodePoint.isUpperCase(): Boolean =
+  Character.isUpperCase(code)
+
+internal actual fun CodePoint.isJavaIdentifierStart(): Boolean =
+  Character.isJavaIdentifierStart(code)
+
+internal actual fun CodePoint.isJavaIdentifierPart(): Boolean =
+  Character.isJavaIdentifierPart(code)
+
+internal actual fun CodePoint.charCount(): Int {
+  return Character.charCount(code)
+}
+
+internal actual fun StringBuilder.appendCodePoint(codePoint: CodePoint): StringBuilder {
+  return appendCodePoint(codePoint.code)
+}
diff --git a/kotlinpoet/src/nonJvmMain/kotlin/com/squareup/kotlinpoet/CodePoint.nonJvm.kt b/kotlinpoet/src/nonJvmMain/kotlin/com/squareup/kotlinpoet/CodePoint.nonJvm.kt
new file mode 100644
index 000000000..302f42034
--- /dev/null
+++ b/kotlinpoet/src/nonJvmMain/kotlin/com/squareup/kotlinpoet/CodePoint.nonJvm.kt
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.kotlinpoet
+
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+internal actual fun StringBuilder.appendCodePoint(codePoint: CodePoint): StringBuilder {
+  // Copied from StringBuilder.kt,
+  // TODO Is this correct?
+  val code = codePoint.code
+  if (code <= Char.MAX_VALUE.code) {
+    append(code.toChar())
+  } else {
+    append(Char.MIN_HIGH_SURROGATE + ((code - 0x10000) ushr 10))
+    append(Char.MIN_LOW_SURROGATE + (code and 0x3ff))
+  }
+  return this
+}
+
+internal actual fun CodePoint.isJavaIdentifierStart(): Boolean {
+  // TODO How check Java identifier start use code point?
+  if (charCount() == 1) {
+    return Char(code).isJavaIdentifierStart()
+  }
+
+  return true
+}
+
+internal actual fun CodePoint.isJavaIdentifierPart(): Boolean {
+  // TODO How check Java identifier part use code point?
+  if (charCount() == 1) {
+    return Char(code).isJavaIdentifierPart()
+  }
+
+  return true
+}
+
+internal actual fun CodePoint.charCount(): Int {
+  return if (code >= 0x10000) 2 else 1
+}
diff --git a/kotlinpoet/src/wasmJsMain/kotlin/com/squareup/kotlinpoet/CodePoint.wasmJs.kt b/kotlinpoet/src/wasmJsMain/kotlin/com/squareup/kotlinpoet/CodePoint.wasmJs.kt
new file mode 100644
index 000000000..22bd4d1ed
--- /dev/null
+++ b/kotlinpoet/src/wasmJsMain/kotlin/com/squareup/kotlinpoet/CodePoint.wasmJs.kt
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.kotlinpoet
+
+internal actual fun String.codePointAt(index: Int): CodePoint {
+  val str = this
+  val code = jsCodePointAt(str, index)
+  return CodePoint(code)
+}
+
+internal actual fun CodePoint.isLowerCase(): Boolean {
+  // TODO Will there be a problem? Is there a better way?
+  val code = this.code
+  val str = jsFromCodePoint(code)
+
+  if (str.length != 1) {
+    return false
+  }
+
+  return str.first().isLowerCase()
+}
+
+internal actual fun CodePoint.isUpperCase(): Boolean {
+  // TODO Will there be a problem? Is there a better way?
+  val code = this.code
+  val str = jsFromCodePoint(code)
+
+  if (str.length != 1) {
+    return false
+  }
+
+  return str.first().isUpperCase()
+}
+
+@Suppress("UNUSED_PARAMETER")
+private fun jsCodePointAt(str: String, index: Int): Int =
+  js("str.codePointAt(index)")
+
+@Suppress("UNUSED_PARAMETER")
+private fun jsFromCodePoint(code: Int): String =
+  js("String.fromCodePoint(code)")