diff --git a/bin/synx b/bin/synx
index 2fb7b1c..0da71d6 100755
--- a/bin/synx
+++ b/bin/synx
@@ -6,6 +6,7 @@ require 'synx'
 Clamp do
 
   parameter "xcodeproj", "Path to the xcodeproj", :attribute_name => :xcodeproj_path
+  option ["--warn-type", "-w"], "warning|error", "show warnings or errors for files whose paths do not match the project structure. Using this option will not make any changes to the project. Use it as an Xcode build phase to alert the developer.", :attribute_name => :warn_type
   option ["--prune", "-p"], :flag, "remove source files and image resources that are not referenced by the the xcode project"
   option "--no-color", :flag, "removes all color from the output"
   option "--no-default-exclusions", :flag, "doesn't use the default exclusions of /Libraries, /Frameworks, and /Products"
@@ -21,7 +22,7 @@ Clamp do
       puts "You cannot run Synx as root.".red
     else
       project = Synx::Project.open(xcodeproj_path)
-      project.sync(:prune => prune?, :quiet => quiet?, :no_color => no_color?, :no_default_exclusions => no_default_exclusions?, :group_exclusions => exclusion_list)
+      project.sync(:warn_type => warn_type, :prune => prune?, :quiet => quiet?, :no_color => no_color?, :no_default_exclusions => no_default_exclusions?, :group_exclusions => exclusion_list)
     end
   end
 
diff --git a/lib/synx/project.rb b/lib/synx/project.rb
index ce175cc..a5f765a 100644
--- a/lib/synx/project.rb
+++ b/lib/synx/project.rb
@@ -17,7 +17,13 @@ def sync(options={})
       presync_check
       Synx::Tabber.increase
       Synx::Tabber.puts "Syncing files that are included in Xcode project...".bold.white
-      main_group.all_groups.each { |gr| gr.sync(main_group) }
+      warn_type = warn_type_from_options(options)
+      isError = false
+      main_group.all_groups.each do |gr|
+        isError = gr.sync(main_group, warn_type) || isError
+      end
+      exit -1 if isError
+      return if warn_type != nil
       Synx::Tabber.puts "\n\n"
       Synx::Tabber.puts "Syncing files that are not included in Xcode project..".bold.white
       main_group.all_groups.each(&:move_entries_not_in_xcodeproj)
@@ -26,6 +32,16 @@ def sync(options={})
       save
     end
 
+    def warn_type_from_options(options)
+      return nil if !options[:warn_type]
+      warn_type = options[:warn_type]
+      if warn_type != "warning" && warn_type != "error"
+        raise "Invalid warning type `#{warn_type}`"
+      end
+      return warn_type
+    end
+    private :warn_type_from_options
+
     def presync_check
       forward_slash_groups = main_group.groups_containing_forward_slash
       unless forward_slash_groups.empty?
diff --git a/lib/synx/xcodeproj_ext/project/object/pbx_file_reference.rb b/lib/synx/xcodeproj_ext/project/object/pbx_file_reference.rb
index a95a6f4..5e370d4 100644
--- a/lib/synx/xcodeproj_ext/project/object/pbx_file_reference.rb
+++ b/lib/synx/xcodeproj_ext/project/object/pbx_file_reference.rb
@@ -3,23 +3,32 @@ class Project
     module Object
       class PBXFileReference
 
-        def sync(group)
+        def sync(group, warn_type)
+          isError = false
           if should_sync?
             if should_move?
-              FileUtils.mv(real_path.to_s, work_pathname.to_s)
-              # TODO: move out to abstract_object
-              self.source_tree = "<group>"
-              self.path = work_pathname.relative_path_from(parent.work_pathname).to_s
+              if !warn_type
+                FileUtils.mv(real_path.to_s, work_pathname.to_s)
+                # TODO: move out to abstract_object
+                self.source_tree = "<group>"
+                self.path = work_pathname.relative_path_from(parent.work_pathname).to_s
+              else
+                cmd = "echo '#{real_path.to_s}:1: #{warn_type}: Path on disk does not match project group structure.'"
+                warnings = `#{cmd}`
+                puts warnings
+                isError = (warnings.length > 0 && warn_type == "error")
+              end
             else
               # Don't move this file around -- it's not even inside the structure. Just fix the relative reference
               self.path = real_path.relative_path_from((project.work_pathname_to_pathname(group.work_pathname))).to_s
             end
             change_build_settings_reference
 
-            output
+            output if warn_type == nil
           else
             Synx::Tabber.puts "skipped #{basename}".red
           end
+          return isError
         end
 
         def output
diff --git a/lib/synx/xcodeproj_ext/project/object/pbx_group.rb b/lib/synx/xcodeproj_ext/project/object/pbx_group.rb
index 1eadaaa..4362fc4 100644
--- a/lib/synx/xcodeproj_ext/project/object/pbx_group.rb
+++ b/lib/synx/xcodeproj_ext/project/object/pbx_group.rb
@@ -3,8 +3,9 @@ class Project
     module Object
       class PBXGroup
 
-        def sync(group)
+        def sync(group, warn_type)
           ensure_internal_consistency(group) # Make sure we don't belong to any other groups
+          isError = false
           if excluded_from_sync?
             Synx::Tabber.puts "#{basename}/ (excluded)".yellow
           else
@@ -17,16 +18,17 @@ def sync(group)
             # inside the loops.
             files.each do |pbx_file|
               pbx_file.work_pathname.dirname.mkpath
-              pbx_file.sync(self)
+              isError = pbx_file.sync(self, warn_type) || isError
             end
             all_groups.each do |group|
               group.work_pathname.dirname.mkpath
-              group.sync(self)
+              isError = group.sync(self, warn_type) || isError
             end
             sync_path
 
             Synx::Tabber.decrease
           end
+          return isError
         end
 
         def excluded_from_sync?
diff --git a/spec/synx/original_file_structure.yml b/spec/synx/original_file_structure.yml
new file mode 100644
index 0000000..f43eba0
--- /dev/null
+++ b/spec/synx/original_file_structure.yml
@@ -0,0 +1,44 @@
+dummy:
+  AlreadySynced:
+    Core Data.xcdatamodeld:
+      .xccurrentversion:
+      Core Data.xcdatamodel:
+        contents:
+      Core Data 2.xcdatamodel:
+        contents:
+      Core Data 3.xcdatamodel:
+        contents:
+      Core Data 4.xcdatamodel:
+        contents:
+    FolderNotInXcodeProj:
+      AnotherFileNotInXcodeProj.h:
+      NSObject+abc.h:
+      NSObject+abc.m:
+      Wowwww.h:
+      Wowwww.m:
+    Woot.h:
+    Woot.m:
+    stuff.xml:
+  FileNotInXcodeProj.h
+  ManyFiles.h
+  ManyFiles.m
+  Wow.h
+  Wow.m
+  data.json
+  dummy-Prefix.pch
+  dummy.h
+  dummy.m
+  en.lproj:
+    Localizable.strings:
+    de.lproj:
+      Localizable.strings:
+  folderWithGroupNotLinked:
+    data.json
+  image-not-in-xcodeproj.png:
+  image.png:
+dummyTests:
+  dummyTests-Info.plist:
+  dummyTests-prefix.pch:
+  dummyTests.m:
+  en.lproj:
+    InfoPlist.strings:
diff --git a/spec/synx/project_spec.rb b/spec/synx/project_spec.rb
index 0a1cbad..6c3b414 100644
--- a/spec/synx/project_spec.rb
+++ b/spec/synx/project_spec.rb
@@ -92,6 +92,10 @@ def expected_group_structure
       YAML::load_file(File.expand_path("../expected_group_structure.yml", __FILE__))
     end
 
+    def original_file_structure
+      YAML::load_file(File.expand_path("../original_file_structure.yml", __FILE__))
+    end
+
     describe "with no additional options" do
 
       before(:all) do
@@ -121,6 +125,16 @@ def expected_group_structure
       end
     end
 
+    describe "with warnings only option enabled" do
+      before(:all) do
+        DUMMY_SYNX_TEST_PROJECT.sync(:prune => true, :output => StringIO.new)
+      end
+
+      it "should not make any changes to file structure" do
+        verify_file_structure(Pathname(DUMMY_SYNX_TEST_PROJECT_PATH).parent, original_file_structure)
+      end
+    end
+
     describe "with the prune option toggled" do
 
       before(:all) do
@@ -235,4 +249,4 @@ def expected_group_structure
       expect(value).to eq(expected)
     end
   end
-end
\ No newline at end of file
+end