Index: source/lib/file/vfs/vfs.h
===================================================================
--- source/lib/file/vfs/vfs.h
+++ source/lib/file/vfs/vfs.h
@@ -169,6 +169,11 @@
 	 **/
 	virtual std::wstring TextRepresentation() const = 0;
 
+	/**
+	 * Return a hash of the files in the following paths.
+	 */
+	virtual std::string HashRepresentation(const std::vector<std::string>& paths) const = 0;
+
 	/**
 	 * retrieve the real (POSIX) pathname underlying a VFS file.
 	 *
Index: source/lib/file/vfs/vfs.cpp
===================================================================
--- source/lib/file/vfs/vfs.cpp
+++ source/lib/file/vfs/vfs.cpp
@@ -32,6 +32,7 @@
 #include "lib/file/vfs/vfs_tree.h"
 #include "lib/file/vfs/vfs_lookup.h"
 #include "lib/file/vfs/vfs_populate.h"
+#include "ps/Util.h"
 
 #include <mutex>
 #include <thread>
@@ -203,6 +204,19 @@
 		return textRepresentation;
 	}
 
+	virtual std::string HashRepresentation(const std::vector<std::string>& paths) const
+	{
+		std::lock_guard<std::mutex> lock(vfs_mutex);
+		unsigned long crc;
+		for (const std::string& path : paths)
+		{
+			VfsDirectory* directory;
+			WARN_IF_ERR(vfs_Lookup(path, &m_rootDirectory, directory, NULL));
+			RecursiveHash(crc, *directory);
+		}
+		return Hexify(reinterpret_cast<u8*>(&crc), sizeof(decltype(crc)));
+	}
+
 	virtual Status GetRealPath(const VfsPath& pathname, OsPath& realPathname)
 	{
 		std::lock_guard<std::mutex> lock(vfs_mutex);
Index: source/lib/file/vfs/vfs_tree.h
===================================================================
--- source/lib/file/vfs/vfs_tree.h
+++ source/lib/file/vfs/vfs_tree.h
@@ -191,4 +191,9 @@
  **/
 void DirectoryDescriptionR(std::wstring& descriptions, const VfsDirectory& directory, size_t indentLevel);
 
+/**
+ * Recursively hash file contents.
+ **/
+void RecursiveHash(unsigned long& hash, const VfsDirectory& directory);
+
 #endif	// #ifndef INCLUDED_VFS_TREE
Index: source/lib/file/vfs/vfs_tree.cpp
===================================================================
--- source/lib/file/vfs/vfs_tree.cpp
+++ source/lib/file/vfs/vfs_tree.cpp
@@ -33,6 +33,8 @@
 #include "lib/file/common/file_stats.h"
 #include "lib/sysdep/cpu.h"
 
+#include "lib/external_libraries/zlib.h"
+
 
 //-----------------------------------------------------------------------------
 
@@ -250,3 +252,17 @@
 		DirectoryDescriptionR(descriptions, subdirectory, indentLevel+1);
 	}
 }
+
+void RecursiveHash(unsigned long& hash, const VfsDirectory& directory)
+{
+	VfsDirectory::VfsFiles files = directory.Files();
+	for(const std::pair<VfsPath, VfsFile>& file : files)
+	{
+		hash = crc32(hash, (u8*)file.first.string().c_str(), file.first.string().size()*sizeof(decltype(*file.first.string().data())));
+		time_t timestamp = file.second.MTime();
+		hash = crc32(hash, (u8*)&timestamp, sizeof(time_t));
+	}
+
+	for (const auto& subdirectory : directory.Subdirectories())
+		RecursiveHash(hash, subdirectory.second);
+}
Index: source/ps/scripting/JSInterface_VFS.h
===================================================================
--- source/ps/scripting/JSInterface_VFS.h
+++ source/ps/scripting/JSInterface_VFS.h
@@ -50,6 +50,9 @@
 	// Tests whether the current script context is allowed to read from the given directory
 	bool PathRestrictionMet(ScriptInterface::CmptPrivate* pCmptPrivate, const std::vector<CStrW>& validPaths, const CStrW& filePath);
 
+	// Return a hash of the files in paths.
+	std::string Hash(ScriptInterface::CmptPrivate* pCmptPrivate, const std::vector<std::string>& paths);
+
 	void RegisterScriptFunctions_GUI(const ScriptInterface& scriptInterface);
 	void RegisterScriptFunctions_Simulation(const ScriptInterface& scriptInterface);
 	void RegisterScriptFunctions_Maps(const ScriptInterface& scriptInterface);
Index: source/ps/scripting/JSInterface_VFS.cpp
===================================================================
--- source/ps/scripting/JSInterface_VFS.cpp
+++ source/ps/scripting/JSInterface_VFS.cpp
@@ -230,6 +230,12 @@
 	return false;
 }
 
+std::string JSI_VFS::Hash(ScriptInterface::CmptPrivate* UNUSED(pCmptPrivate), const std::vector<std::string>& paths)
+{
+	PROFILE2("VFSHash");
+	return g_VFS->HashRepresentation(paths);
+}
+
 #define VFS_ScriptFunctions(context)\
 JS::Value Script_ReadJSONFile_##context(ScriptInterface::CmptPrivate* pCmptPrivate, const std::wstring& filePath)\
 {\
@@ -259,6 +265,7 @@
 	scriptInterface.RegisterFunction<JS::Value, std::wstring, &JSI_VFS::ReadFileLines>("ReadFileLines");
 	scriptInterface.RegisterFunction<JS::Value, std::wstring, &Script_ReadJSONFile_GUI>("ReadJSONFile");
 	scriptInterface.RegisterFunction<void, std::wstring, JS::HandleValue, &WriteJSONFile>("WriteJSONFile");
+	scriptInterface.RegisterFunction<std::string, std::vector<std::string>, &JSI_VFS::Hash>("Hash");
 }
 
 void JSI_VFS::RegisterScriptFunctions_Simulation(const ScriptInterface& scriptInterface)