diff --git a/java/ql/lib/semmle/code/java/StringCheck.qll b/java/ql/lib/semmle/code/java/StringCheck.qll
new file mode 100644
index 0000000000000..eaf15fdfa2907
--- /dev/null
+++ b/java/ql/lib/semmle/code/java/StringCheck.qll
@@ -0,0 +1,14 @@
+/**
+ * Provides classes and predicates for reasoning about checking characterizations about strings.
+ */
+
+import java
+
+/**
+ * Holds if `ma` is a call to a method that checks a partial string match.
+ */
+predicate isStringPartialMatch(MethodAccess ma) {
+    ma.getMethod().getDeclaringType() instanceof TypeString and
+    ma.getMethod().getName() =
+      ["contains", "startsWith", "matches", "regionMatches", "indexOf", "lastIndexOf"]
+  }
diff --git a/java/ql/lib/semmle/code/java/frameworks/apache/Lang.qll b/java/ql/lib/semmle/code/java/frameworks/apache/Lang.qll
index b536539670eeb..f691952ac1fe7 100644
--- a/java/ql/lib/semmle/code/java/frameworks/apache/Lang.qll
+++ b/java/ql/lib/semmle/code/java/frameworks/apache/Lang.qll
@@ -37,3 +37,12 @@ private class ApacheStrBuilderFluentMethod extends FluentMethod {
     this.getReturnType().(RefType).hasQualifiedName("org.apache.commons.lang3.text", "StrBuilder")
   }
 }
+
+/**
+ * The class ``org.apache.commons.lang.SystemUtils` or `org.apache.commons.lang3.SystemUtils`.
+ */
+class ApacheSystemUtilis extends Class {
+  ApacheSystemUtilis() {
+    this.hasQualifiedName(["org.apache.commons.lang", "org.apache.commons.lang3"], "SystemUtils")
+  }
+}
diff --git a/java/ql/lib/semmle/code/java/os/OSCheck.qll b/java/ql/lib/semmle/code/java/os/OSCheck.qll
new file mode 100644
index 0000000000000..e6d384b7c84db
--- /dev/null
+++ b/java/ql/lib/semmle/code/java/os/OSCheck.qll
@@ -0,0 +1,93 @@
+/**
+ * Provides classes and predicates for guards that check for the current OS.
+ */
+
+import java
+import semmle.code.java.controlflow.Guards
+private import semmle.code.java.frameworks.apache.Lang
+private import semmle.code.java.dataflow.DataFlow
+private import semmle.code.java.StringCheck
+
+/**
+ * A complimentatry guard that checks if the current platform is Windows.
+ */
+abstract class IsWindowsGuard extends Guard { }
+
+/**
+ * A complimentatry guard that checks if the current platform is unix or unix-like.
+ */
+abstract class IsUnixGuard extends Guard { }
+
+/**
+ * Holds when the MethodAccess is a call to check the current OS using either the upper case `osUpperCase` or lower case `osLowerCase` string constants.
+ */
+bindingset[osUpperCase, osLowerCase]
+private predicate isOsFromSystemProp(MethodAccess ma, string osUpperCase, string osLowerCase) {
+  exists(MethodAccessSystemGetProperty sgpMa |
+    sgpMa.hasCompileTimeConstantGetPropertyName("os.name")
+  |
+    DataFlow::localExprFlow(sgpMa, ma.getQualifier()) and // Call from System.getProperty to some partial match method
+    ma.getAnArgument().(CompileTimeConstantExpr).getStringValue().matches(osUpperCase)
+    or
+    exists(MethodAccess toLowerCaseMa |
+      toLowerCaseMa.getMethod() =
+        any(Method m | m.getDeclaringType() instanceof TypeString and m.hasName("toLowerCase"))
+    |
+      DataFlow::localExprFlow(sgpMa, toLowerCaseMa.getQualifier()) and // Call from System.getProperty to toLowerCase
+      DataFlow::localExprFlow(toLowerCaseMa, ma.getQualifier()) and // Call from toLowerCase to some partial match method
+      ma.getAnArgument().(CompileTimeConstantExpr).getStringValue().matches(osLowerCase)
+    )
+  ) and
+  isStringPartialMatch(ma)
+}
+
+private class IsWindowsFromSystemProp extends IsWindowsGuard instanceof MethodAccess {
+  IsWindowsFromSystemProp() { isOsFromSystemProp(this, "Window%", "window%") }
+}
+
+private class IsUnixFromSystemProp extends IsUnixGuard instanceof MethodAccess {
+  IsUnixFromSystemProp() {
+    isOsFromSystemProp(this, ["Mac%", "Linux%", "LINUX%"], ["mac%", "linux%"])
+  }
+}
+
+private predicate isOsFromApacheCommons(FieldAccess fa, string fieldName) {
+  exists(Field f | f = fa.getField() |
+    f.getDeclaringType() instanceof ApacheSystemUtilis and
+    f.hasName(fieldName)
+  )
+}
+
+private class IsWindowsFromApacheCommons extends IsWindowsGuard instanceof FieldAccess {
+  IsWindowsFromApacheCommons() { isOsFromApacheCommons(this, "IS_OS_WINDOWS%") }
+}
+
+private class IsUnixFromApacheCommons extends IsUnixGuard instanceof FieldAccess {
+  IsUnixFromApacheCommons() { isOsFromApacheCommons(this, ["IS_OS_UNIX"]) }
+}
+
+/**
+ * A guard that checks if the `java.nio.file.FileSystem` supports posix file permissions.
+ * This is often used to infer if the OS is unix-based.
+ * Looks for calls to `contains("poxix")` on the `supportedFileAttributeViews` method returned by `FileSystem`.
+ */
+private class IsUnixFromPosixFromFileSystem extends IsUnixGuard instanceof MethodAccess {
+  IsUnixFromPosixFromFileSystem() {
+    exists(Method m | m = this.getMethod() |
+      m.getDeclaringType()
+          .getASupertype*()
+          .getSourceDeclaration()
+          .hasQualifiedName("java.util", "Set") and
+      m.hasName("contains")
+    ) and
+    this.getArgument(0).(CompileTimeConstantExpr).getStringValue() = "posix" and
+    exists(Method supportedFileAttribtueViewsMethod |
+      supportedFileAttribtueViewsMethod.hasName("supportedFileAttributeViews") and
+      supportedFileAttribtueViewsMethod.getDeclaringType() instanceof TypeFileSystem
+    |
+      DataFlow::localExprFlow(any(MethodAccess ma |
+          ma.getMethod() = supportedFileAttribtueViewsMethod
+        ), super.getQualifier())
+    )
+  }
+}
diff --git a/java/ql/src/experimental/Security/CWE/CWE-552/UnsafeUrlForward.qll b/java/ql/src/experimental/Security/CWE/CWE-552/UnsafeUrlForward.qll
index 5c07b67f43d97..9ca5f3af0a4e7 100644
--- a/java/ql/src/experimental/Security/CWE/CWE-552/UnsafeUrlForward.qll
+++ b/java/ql/src/experimental/Security/CWE/CWE-552/UnsafeUrlForward.qll
@@ -5,6 +5,7 @@ import semmle.code.java.dataflow.FlowSources
 import semmle.code.java.frameworks.Servlets
 import semmle.code.java.frameworks.spring.SpringWeb
 import semmle.code.java.security.RequestForgery
+private import semmle.code.java.StringCheck
 private import semmle.code.java.dataflow.StringPrefixes
 
 /** A sink for unsafe URL forward vulnerabilities. */
@@ -167,15 +168,6 @@ private class URLEncodingBarrierGuard extends UnsafeUrlForwardBarrierGuard insta
   }
 }
 
-/**
- * Holds if `ma` is a call to a method that checks a partial string match.
- */
-private predicate isStringPartialMatch(MethodAccess ma) {
-  ma.getMethod().getDeclaringType() instanceof TypeString and
-  ma.getMethod().getName() =
-    ["contains", "startsWith", "matches", "regionMatches", "indexOf", "lastIndexOf"]
-}
-
 /**
  * Holds if `ma` is a call to a method of `java.nio.file.Path` that checks a partial path match.
  */
diff --git a/java/ql/test/library-tests/os/Test.java b/java/ql/test/library-tests/os/Test.java
new file mode 100644
index 0000000000000..ce78bbe63785d
--- /dev/null
+++ b/java/ql/test/library-tests/os/Test.java
@@ -0,0 +1,34 @@
+import java.nio.file.FileSystems;
+import java.nio.file.Path;
+
+public class Test {
+    void test() {
+        if (System.getProperty("os.name").contains("Windows")) {
+            
+        }
+
+        if (System.getProperty("os.name").toLowerCase().contains("windows")) {
+            
+        }
+
+        if (System.getProperty("os.name").contains("Linux")) {
+            
+        }
+
+        if (System.getProperty("os.name").contains("Mac OS X")) {
+            
+        }
+
+        if (System.getProperty("os.name").toLowerCase().contains("mac")) {
+            
+        }
+
+        if (Path.of("whatever").getFileSystem().supportedFileAttributeViews().contains("posix")) {
+
+        }
+
+        if (FileSystems.getDefault().supportedFileAttributeViews().contains("posix")) {
+
+        }
+    }
+}
diff --git a/java/ql/test/library-tests/os/unix-test.expected b/java/ql/test/library-tests/os/unix-test.expected
new file mode 100644
index 0000000000000..8fa5944143d8c
--- /dev/null
+++ b/java/ql/test/library-tests/os/unix-test.expected
@@ -0,0 +1,5 @@
+| Test.java:14:13:14:59 | contains(...) |
+| Test.java:18:13:18:62 | contains(...) |
+| Test.java:22:13:22:71 | contains(...) |
+| Test.java:26:13:26:95 | contains(...) |
+| Test.java:30:13:30:84 | contains(...) |
diff --git a/java/ql/test/library-tests/os/unix-test.ql b/java/ql/test/library-tests/os/unix-test.ql
new file mode 100644
index 0000000000000..b2b48d2df7e6f
--- /dev/null
+++ b/java/ql/test/library-tests/os/unix-test.ql
@@ -0,0 +1,5 @@
+import default
+import semmle.code.java.os.OSCheck
+
+from IsUnixGuard isUnix
+select isUnix
\ No newline at end of file
diff --git a/java/ql/test/library-tests/os/windows-test.expected b/java/ql/test/library-tests/os/windows-test.expected
new file mode 100644
index 0000000000000..38fa6b7a17930
--- /dev/null
+++ b/java/ql/test/library-tests/os/windows-test.expected
@@ -0,0 +1,2 @@
+| Test.java:6:13:6:61 | contains(...) |
+| Test.java:10:13:10:75 | contains(...) |
diff --git a/java/ql/test/library-tests/os/windows-test.ql b/java/ql/test/library-tests/os/windows-test.ql
new file mode 100644
index 0000000000000..4027d6da8a1e1
--- /dev/null
+++ b/java/ql/test/library-tests/os/windows-test.ql
@@ -0,0 +1,5 @@
+import default
+import semmle.code.java.os.OSCheck
+
+from IsWindowsGuard isWindows
+select isWindows
\ No newline at end of file