diff --git a/core/api/kotlinx-io-core.api b/core/api/kotlinx-io-core.api
index e28bc59cd..25b6fa3a0 100644
--- a/core/api/kotlinx-io-core.api
+++ b/core/api/kotlinx-io-core.api
@@ -91,6 +91,7 @@ public abstract interface annotation class kotlinx/io/InternalIoApi : java/lang/
 public final class kotlinx/io/JvmCoreKt {
 	public static final fun asSink (Ljava/io/OutputStream;)Lkotlinx/io/RawSink;
 	public static final fun asSource (Ljava/io/InputStream;)Lkotlinx/io/RawSource;
+	public static final fun getSystemLineSeparator ()Ljava/lang/String;
 }
 
 public abstract interface class kotlinx/io/RawSink : java/io/Flushable, java/lang/AutoCloseable {
diff --git a/core/api/kotlinx-io-core.klib.api b/core/api/kotlinx-io-core.klib.api
index 02d9050a7..c3e48dc9c 100644
--- a/core/api/kotlinx-io-core.klib.api
+++ b/core/api/kotlinx-io-core.klib.api
@@ -233,6 +233,8 @@ final val kotlinx.io.unsafe/SegmentReadContextImpl // kotlinx.io.unsafe/SegmentR
     final fun <get-SegmentReadContextImpl>(): kotlinx.io.unsafe/SegmentReadContext // kotlinx.io.unsafe/SegmentReadContextImpl.<get-SegmentReadContextImpl>|<get-SegmentReadContextImpl>(){}[0]
 final val kotlinx.io.unsafe/SegmentWriteContextImpl // kotlinx.io.unsafe/SegmentWriteContextImpl|{}SegmentWriteContextImpl[0]
     final fun <get-SegmentWriteContextImpl>(): kotlinx.io.unsafe/SegmentWriteContext // kotlinx.io.unsafe/SegmentWriteContextImpl.<get-SegmentWriteContextImpl>|<get-SegmentWriteContextImpl>(){}[0]
+final val kotlinx.io/SystemLineSeparator // kotlinx.io/SystemLineSeparator|{}SystemLineSeparator[0]
+    final fun <get-SystemLineSeparator>(): kotlin/String // kotlinx.io/SystemLineSeparator.<get-SystemLineSeparator>|<get-SystemLineSeparator>(){}[0]
 
 final fun (kotlinx.io.files/Path).kotlinx.io.files/sink(): kotlinx.io/Sink // kotlinx.io.files/sink|sink@kotlinx.io.files.Path(){}[0]
 final fun (kotlinx.io.files/Path).kotlinx.io.files/source(): kotlinx.io/Source // kotlinx.io.files/source|source@kotlinx.io.files.Path(){}[0]
diff --git a/core/apple/src/-PlatformApple.kt b/core/apple/src/-PlatformApple.kt
new file mode 100644
index 000000000..1686fb31d
--- /dev/null
+++ b/core/apple/src/-PlatformApple.kt
@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2025 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
+ */
+
+package kotlinx.io
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * The value of this property is always `"\n"`.
+ */
+public actual val SystemLineSeparator: String = "\n"
diff --git a/core/build.gradle.kts b/core/build.gradle.kts
index 2799ec449..b47ed2b8e 100644
--- a/core/build.gradle.kts
+++ b/core/build.gradle.kts
@@ -3,6 +3,8 @@
  * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
  */
 
+@file:OptIn(ExperimentalWasmDsl::class)
+
 import org.gradle.internal.os.OperatingSystem
 import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 
@@ -29,10 +31,23 @@ kotlin {
                 useMocha {
                     timeout = "300s"
                 }
+                filter.setExcludePatterns("kotlinx.io.files.*")
+            }
+        }
+    }
+    wasmJs {
+        nodejs()
+        /*
+        browser {
+            testTask {
+                useKarma {
+                    // how to configure browsers available in CI?
+                }
+                filter.setExcludePatterns("kotlinx.io.files.*")
             }
         }
+         */
     }
-    @OptIn(ExperimentalWasmDsl::class)
     wasmWasi {
         nodejs {
             testTask {
diff --git a/core/common/src/-CommonPlatform.kt b/core/common/src/-CommonPlatform.kt
index a0c1e75d9..21db552a7 100644
--- a/core/common/src/-CommonPlatform.kt
+++ b/core/common/src/-CommonPlatform.kt
@@ -38,3 +38,8 @@ public expect open class EOFException : IOException {
     public constructor()
     public constructor(message: String?)
 }
+
+/**
+ * True if the underlying platform is Windows (assuming that it's possible to get this info).
+ */
+internal expect val isWindows: Boolean
diff --git a/core/common/src/Core.kt b/core/common/src/Core.kt
index be72be491..05977a5c9 100644
--- a/core/common/src/Core.kt
+++ b/core/common/src/Core.kt
@@ -43,3 +43,12 @@ private class DiscardingSink : RawSink {
   override fun flush() {}
   override fun close() {}
 }
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * The value of this property is platform-specific, but usually it is either `"\n"` or `"\r\n"`.
+ *
+ * See the documentation for a particular platform to get more information about the value of this property.
+ */
+public expect val SystemLineSeparator: String
diff --git a/core/common/src/files/FileSystem.kt b/core/common/src/files/FileSystem.kt
index 46c40af65..2a2ff704b 100644
--- a/core/common/src/files/FileSystem.kt
+++ b/core/common/src/files/FileSystem.kt
@@ -214,5 +214,3 @@ public expect class FileNotFoundException(message: String?) : IOException
 
 internal const val WindowsPathSeparator: Char = '\\'
 internal const val UnixPathSeparator: Char = '/'
-
-internal expect val isWindows: Boolean
diff --git a/core/common/test/LineSeparatorTest.kt b/core/common/test/LineSeparatorTest.kt
new file mode 100644
index 000000000..ca03a9874
--- /dev/null
+++ b/core/common/test/LineSeparatorTest.kt
@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2025 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
+ */
+
+package kotlinx.io
+
+import kotlinx.io.isWindows
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class LineSeparatorTest {
+    @Test
+    public fun testLineSeparator() {
+        if (isWindows) {
+            assertEquals("\r\n", SystemLineSeparator)
+        } else {
+            assertEquals("\n", SystemLineSeparator)
+        }
+    }
+}
diff --git a/core/common/test/files/SmokeFileTestWindows.kt b/core/common/test/files/SmokeFileTestWindows.kt
index 23994807e..5c1178419 100644
--- a/core/common/test/files/SmokeFileTestWindows.kt
+++ b/core/common/test/files/SmokeFileTestWindows.kt
@@ -5,6 +5,7 @@
 
 package kotlinx.io.files
 
+import kotlinx.io.isWindows
 import kotlin.test.*
 
 class SmokeFileTestWindows {
diff --git a/core/js/src/-PlatformJs.kt b/core/js/src/-PlatformJs.kt
index 7e198e25c..5f868d230 100644
--- a/core/js/src/-PlatformJs.kt
+++ b/core/js/src/-PlatformJs.kt
@@ -31,3 +31,27 @@ internal actual fun withCaughtException(block: () -> Unit): Throwable? {
         return t
     }
 }
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * Value of this property depends on [Navigator.platform](https://developer.mozilla.org/en-US/docs/Web/API/Navigator/platform):
+ * it is `"\r\n"` on Windows, and `"\n"` on all other platforms.
+ */
+public actual val SystemLineSeparator: String by lazy {
+    if (isWindows) {
+        "\r\n"
+    } else {
+        "\n"
+    }
+}
+
+internal actual val isWindows: Boolean by lazy {
+    getPlatformName().startsWith("Win", ignoreCase = true)
+}
+
+private fun getPlatformName(): String = js(
+    """
+        (typeof navigator !== "undefined" && navigator.platform) || "unknown"
+    """
+)
diff --git a/core/jvm/src/-JvmPlatform.kt b/core/jvm/src/-JvmPlatform.kt
index 92e17424a..0d65280ef 100644
--- a/core/jvm/src/-JvmPlatform.kt
+++ b/core/jvm/src/-JvmPlatform.kt
@@ -24,3 +24,5 @@ package kotlinx.io
 public actual typealias IOException = java.io.IOException
 
 public actual typealias EOFException = java.io.EOFException
+
+internal actual val isWindows: Boolean = System.getProperty("os.name")?.startsWith("Windows") ?: false
diff --git a/core/jvm/src/JvmCore.kt b/core/jvm/src/JvmCore.kt
index e714f7740..a556c8916 100644
--- a/core/jvm/src/JvmCore.kt
+++ b/core/jvm/src/JvmCore.kt
@@ -109,3 +109,10 @@ internal val AssertionError.isAndroidGetsocknameError: Boolean
     get() {
         return cause != null && message?.contains("getsockname failed") ?: false
     }
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * Returns the same value as [System.lineSeparator].
+ */
+public actual val SystemLineSeparator: String = System.lineSeparator()
diff --git a/core/jvm/src/files/FileSystemJvm.kt b/core/jvm/src/files/FileSystemJvm.kt
index b85ebdb7e..d19e75216 100644
--- a/core/jvm/src/files/FileSystemJvm.kt
+++ b/core/jvm/src/files/FileSystemJvm.kt
@@ -113,5 +113,3 @@ public actual val SystemFileSystem: FileSystem = object : SystemFileSystemImpl()
 public actual val SystemTemporaryDirectory: Path = Path(System.getProperty("java.io.tmpdir"))
 
 public actual typealias FileNotFoundException = java.io.FileNotFoundException
-
-internal actual val isWindows: Boolean = System.getProperty("os.name")?.startsWith("Windows") ?: false
diff --git a/core/jvm/test/files/SmokeFileTestWindowsJVM.kt b/core/jvm/test/files/SmokeFileTestWindowsJVM.kt
index 76d6ec4bc..d873a68b8 100644
--- a/core/jvm/test/files/SmokeFileTestWindowsJVM.kt
+++ b/core/jvm/test/files/SmokeFileTestWindowsJVM.kt
@@ -5,6 +5,7 @@
 
 package kotlinx.io.files
 
+import kotlinx.io.isWindows
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
diff --git a/core/mingw/src/-PlatformMingw.kt b/core/mingw/src/-PlatformMingw.kt
new file mode 100644
index 000000000..c1ab9e3c7
--- /dev/null
+++ b/core/mingw/src/-PlatformMingw.kt
@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2025 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
+ */
+
+package kotlinx.io
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * The value of this property is always `"\r\n"`.
+ */
+public actual val SystemLineSeparator: String = "\r\n"
diff --git a/core/native/src/-NonJvmPlatform.kt b/core/native/src/-NonJvmPlatform.kt
index 9294c3190..e25daf3c7 100644
--- a/core/native/src/-NonJvmPlatform.kt
+++ b/core/native/src/-NonJvmPlatform.kt
@@ -20,6 +20,8 @@
  */
 package kotlinx.io
 
+import kotlin.experimental.ExperimentalNativeApi
+
 public actual open class IOException : Exception {
     public actual constructor() : super()
 
@@ -37,3 +39,6 @@ public actual open class EOFException : IOException {
 
     public constructor(message: String?, cause: Throwable?) : super(message, cause)
 }
+
+@OptIn(ExperimentalNativeApi::class)
+internal actual val isWindows: Boolean = Platform.osFamily == OsFamily.WINDOWS
diff --git a/core/native/src/files/FileSystemNative.kt b/core/native/src/files/FileSystemNative.kt
index 1fa719b15..9a1ce9385 100644
--- a/core/native/src/files/FileSystemNative.kt
+++ b/core/native/src/files/FileSystemNative.kt
@@ -121,9 +121,6 @@ public actual open class FileNotFoundException actual constructor(
 // 777 in octal, rwx for all (owner, group and others).
 internal const val PermissionAllowAll: UShort = 511u
 
-@OptIn(ExperimentalNativeApi::class)
-internal actual val isWindows: Boolean = Platform.osFamily == OsFamily.WINDOWS
-
 internal expect class OpaqueDirEntry : AutoCloseable {
     fun readdir(): String?
     override fun close()
diff --git a/core/nodeFilesystemShared/src/files/FileSystemNodeJs.kt b/core/nodeFilesystemShared/src/files/FileSystemNodeJs.kt
index 810b5ba02..ba36e42b0 100644
--- a/core/nodeFilesystemShared/src/files/FileSystemNodeJs.kt
+++ b/core/nodeFilesystemShared/src/files/FileSystemNodeJs.kt
@@ -128,4 +128,3 @@ public actual open class FileNotFoundException actual constructor(
     message: String?,
 ) : IOException(message)
 
-internal actual val isWindows = os.platform() == "win32"
diff --git a/core/nodeFilesystemShared/src/node/os.kt b/core/nodeFilesystemShared/src/node/os.kt
index 431d60a8f..6a55a0691 100644
--- a/core/nodeFilesystemShared/src/node/os.kt
+++ b/core/nodeFilesystemShared/src/node/os.kt
@@ -16,6 +16,11 @@ internal external interface Os {
      * See https://nodejs.org/api/os.html#osplatform
      */
     fun platform(): String
+
+    /**
+     * See https://nodejs.org/api/os.html#oseol
+     */
+    val EOL: String
 }
 
 internal expect val os: Os
diff --git a/core/nodeFilesystemShared/test/files/SmokeFileTestWindowsNodeJs.kt b/core/nodeFilesystemShared/test/files/SmokeFileTestWindowsNodeJs.kt
index bb84a4d03..d85fdaa0d 100644
--- a/core/nodeFilesystemShared/test/files/SmokeFileTestWindowsNodeJs.kt
+++ b/core/nodeFilesystemShared/test/files/SmokeFileTestWindowsNodeJs.kt
@@ -5,6 +5,7 @@
 
 package kotlinx.io.files
 
+import kotlinx.io.isWindows
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertNull
diff --git a/core/unix/src/-PlatformUnix.kt b/core/unix/src/-PlatformUnix.kt
new file mode 100644
index 000000000..1686fb31d
--- /dev/null
+++ b/core/unix/src/-PlatformUnix.kt
@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2025 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
+ */
+
+package kotlinx.io
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * The value of this property is always `"\n"`.
+ */
+public actual val SystemLineSeparator: String = "\n"
diff --git a/core/wasmJs/src/-PlatformWasmJs.kt b/core/wasmJs/src/-PlatformWasmJs.kt
index d93280360..b3fabfc3b 100644
--- a/core/wasmJs/src/-PlatformWasmJs.kt
+++ b/core/wasmJs/src/-PlatformWasmJs.kt
@@ -23,3 +23,25 @@ private fun catchJsThrowable(block: () -> Unit): JsAny? = js("""{
     }
 }""")
 
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * Value of this property depends on [Navigator.platform](https://developer.mozilla.org/en-US/docs/Web/API/Navigator/platform):
+ * it is `"\r\n"` on Windows, and `"\n"` on all other platforms.
+ */
+public actual val SystemLineSeparator: String by lazy {
+    if (isWindows) {
+        "\r\n"
+    } else {
+        "\n"
+    }
+}
+
+@JsFun("""
+    () => (typeof navigator !== "undefined" && navigator.platform) || "unknown"
+""")
+private external fun getPlatformName(): String
+
+internal actual val isWindows by lazy {
+    getPlatformName().startsWith("Win", ignoreCase = true)
+}
diff --git a/core/wasmWasi/src/-PlatformWasmWasi.kt b/core/wasmWasi/src/-PlatformWasmWasi.kt
new file mode 100644
index 000000000..4087fa4ad
--- /dev/null
+++ b/core/wasmWasi/src/-PlatformWasmWasi.kt
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2025 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
+ */
+
+package kotlinx.io
+
+/**
+ * Sequence of characters used as a line separator by the underlying platform.
+ *
+ * The value of this property is always `"\n"`.
+ */
+public actual val SystemLineSeparator: String = "\n"
+
+/**
+ * The property affects paths processing and [SystemLineSeparator].
+ * In Wasi, paths are always '/'-delimited, so it does not really affect paths processing.
+ * As of [SystemLineSeparator], it seems like there's not so much we can do right now.
+ */
+internal actual val isWindows: Boolean get() = false
diff --git a/core/wasmWasi/src/files/FileSystemWasm.kt b/core/wasmWasi/src/files/FileSystemWasm.kt
index 252fbe30b..8ab0860c2 100644
--- a/core/wasmWasi/src/files/FileSystemWasm.kt
+++ b/core/wasmWasi/src/files/FileSystemWasm.kt
@@ -372,9 +372,6 @@ public actual open class FileNotFoundException actual constructor(
     message: String?,
 ) : IOException(message)
 
-// The property affects only paths processing and in Wasi paths are always '/'-delimited.
-internal actual val isWindows: Boolean get() = false
-
 internal object PreOpens {
     data class PreOpen(val path: Path, val fd: Int)
 
diff --git a/core/wasmWasi/test/WasiFsTest.kt b/core/wasmWasi/test/WasiFsTest.kt
index 40a835be5..9296f666a 100644
--- a/core/wasmWasi/test/WasiFsTest.kt
+++ b/core/wasmWasi/test/WasiFsTest.kt
@@ -7,6 +7,7 @@ package kotlinx.io.files
 
 import kotlinx.io.IOException
 import kotlinx.io.buffered
+import kotlinx.io.isWindows
 import kotlinx.io.readLine
 import kotlinx.io.writeString
 import kotlin.test.*