diff --git a/src/backend/fileheader.h b/src/backend/fileheader.h
index 4918281f5..03058181c 100644
--- a/src/backend/fileheader.h
+++ b/src/backend/fileheader.h
@@ -26,7 +26,11 @@
 
 LUMIERA_ERROR_DECLARE (FILEHEADER_NOWRITE);
 LUMIERA_ERROR_DECLARE (FILEHEADER_HEADER);
+LUMIERA_ERROR_DECLARE (FILEHEADER_FLAGS);
+LUMIERA_ERROR_DECLARE (FILEHEADER_FLAGSPACE);
+LUMIERA_ERROR_DECLARE (FILEHEADER_ENDIANESS);
 
+#define LUMIERA_FILEHEADER_ENDIANMAGIC 0x0123456789ABCDEFULL
 
 typedef struct lumiera_fileheader_struct lumiera_fileheader;
 typedef lumiera_fileheader* LumieraFileheader;
@@ -34,12 +38,6 @@ typedef lumiera_fileheader* LumieraFileheader;
 typedef struct lumiera_fileheader_raw_struct lumiera_fileheader_raw;
 typedef lumiera_fileheader_raw* LumieraFileheaderRaw;
 
-typedef struct lumiera_fileheaderext_struct lumiera_fileheaderext;
-typedef lumiera_fileheaderext* LumieraFileheaderext;
-
-typedef struct lumiera_fileheaderext_raw_struct lumiera_fileheaderext_raw;
-typedef lumiera_fileheaderext_raw* LumieraFileheaderextRaw;
-
 
 #include "backend/file.h"
 
@@ -79,13 +77,35 @@ struct LUMIERA_PACKED lumiera_fileheader_raw_struct
   /** always '\n' */
   char newline1;
   /** freeform string, comment or so on, initialized to spaces */
-  char meta[22];
+  char meta[15];
   /** always '\n' */
   char newline2;
+
+  /** initialized to spaces, flags are single chars, unsorted */
+  char flags[6];
+  /** always '\n' */
+  char newline3;
   /** always '\0' */
   char null;
+
+  /* natively written 0x0123456789ABCDEFULL by the host created this */
+  uint64_t endianess_mark;
 };
 
+/**
+ * Fileheader flags are chars to make this easily inspectable, these add another human readable line to the header
+ */
+
+/** file is clean */
+#define LUMIERA_FILEHEADER_FLAG_CLEAN "c"
+
+/** check for host order endianess */
+#define LUMIERA_FILEHEADER_FLAG_ENDIANESS "e"
+
+
+
+
+
 /**
  * A fileheader object encapsulates the underlying mmap object which keeps the
  * raw header data in memory and and the dereferenced thereof.
@@ -106,10 +126,11 @@ struct lumiera_fileheader_struct
  * @param version version number for the header (should be incremented after changes)
  *                the value '0' is reserved for experimental versions.
  * @param size The actual size of all header data, including following format specific data.
+ * @param flags initial flags which should be set (dont include CLEAN here, should be set on close)
  * @return A lumiera_fileheader object by value, .header and .map are set to NULL on error.
  */
 lumiera_fileheader
-lumiera_fileheader_create (LumieraFile file, char* fourcc, int version, size_t size);
+lumiera_fileheader_create (LumieraFile file, char* fourcc, int version, size_t size, const char* flags);
 
 
 /**
@@ -118,20 +139,23 @@ lumiera_fileheader_create (LumieraFile file, char* fourcc, int version, size_t s
  * and must be closed after use. The File should be locked for operations on the fileheader.
  * @param file The file on which to open the header.
  * @param fourcc pointer to a string of length 4 with the expected identifier for the file
- * @param size The actual size of all header data, including following format specific data.
+ * @param size The actual size of all header data, including following format specific data
+ * @param flags_expected expect this flags being set
+ * @param flags_remov remove this flags when opening
  * @return A lumiera_fileheader object by value, .header and .map are set to NULL on error.
  */
 lumiera_fileheader
-lumiera_fileheader_open (LumieraFile file, char* fourcc, size_t size);
+lumiera_fileheader_open (LumieraFile file, char* fourcc, size_t size, const char* flags_expected, const char* flags_remove);
 
 
 /**
  * Closes a previously created or opened fileheader.
  * @param self the fileheader to close.
- * no errors, no nothing returned
+ * @param flags_add set this flags if not already set
+ * no errors, no nothing returned (yet)
  */
 void
-lumiera_fileheader_close (LumieraFileheader self);
+lumiera_fileheader_close (LumieraFileheader self, const char* flags_add);
 
 
 /**
@@ -143,8 +167,25 @@ int
 lumiera_fileheader_version (LumieraFileheader self);
 
 
+/**
+ * check if all flags given from some sets are either set or not.
+ */
+int
+lumiera_fileheader_flags_validate (LumieraFileheader self, const char* expected, const char* unexpected);
 
 
+/**
+ * Sets flags if not already set
+ */
+LumieraFileheader
+lumiera_fileheader_flags_set (LumieraFileheader self, const char* flags);
+
+/**
+ * Clear flags if present
+ */
+LumieraFileheader
+lumiera_fileheader_flags_clear (LumieraFileheader self, const char* flags);
+
 
 #endif
 /*
diff --git a/tests/31fileheader.tests b/tests/31fileheader.tests
index d8eb8c832..8f89e2f0f 100644
--- a/tests/31fileheader.tests
+++ b/tests/31fileheader.tests
@@ -3,6 +3,7 @@ TESTING "fileheader access" ./test-fileheader
 TEST "fileheader, basic creation" create_basic <<END
 err: ECHO: .*: fileheader: TEST  0
 err: ECHO: .*: .*          $
+err: ECHO: .*: main: e
 err: ECHO: .*: :
 END
 
@@ -20,6 +21,15 @@ END
 TEST "fileheader, reopen" acquire_basic <<END
 err: ECHO: .*: fileheader: TEST  0
 err: ECHO: .*: .*          $
+err: ECHO: .*: main: e
+err: ECHO: .*: :
+END
+
+
+TEST "fileheader, reopen" acquire_basic_readonly <<END
+err: ECHO: .*: fileheader: TEST  0
+err: ECHO: .*: .*          $
+err: ECHO: .*: main: e
 err: ECHO: .*: :
 END
 
diff --git a/tests/backend/test-fileheader.c b/tests/backend/test-fileheader.c
index b5f4a099d..5b206c7da 100644
--- a/tests/backend/test-fileheader.c
+++ b/tests/backend/test-fileheader.c
@@ -37,13 +37,13 @@ TEST (create_basic)
 
   LUMIERA_FILE_WRLOCK_SECTION (NOBUG_ON, file)
     {
-      lumiera_fileheader header = lumiera_fileheader_create (file, "TEST", 0, sizeof (lumiera_fileheader_raw));
+      lumiera_fileheader header = lumiera_fileheader_create (file, "TEST", 0, sizeof (lumiera_fileheader_raw), LUMIERA_FILEHEADER_FLAG_ENDIANESS);
 
       CHECK (lumiera_error_peek() == NULL);
 
       ECHO ("fileheader: %s:", (char*)header.header);
 
-      lumiera_fileheader_close (&header);
+      lumiera_fileheader_close (&header, LUMIERA_FILEHEADER_FLAG_CLEAN);
     }
 
   lumiera_file_delete (file);
@@ -60,11 +60,11 @@ TEST (create_nowrite)
 
   LUMIERA_FILE_RDLOCK_SECTION (NOBUG_ON, file)
     {
-      lumiera_fileheader header = lumiera_fileheader_create (file, "TEST", 0, sizeof (lumiera_fileheader));
+      lumiera_fileheader header = lumiera_fileheader_create (file, "TEST", 0, sizeof (lumiera_fileheader), NULL);
 
       CHECK(lumiera_error() == LUMIERA_ERROR_FILEHEADER_NOWRITE);
 
-      lumiera_fileheader_close (&header);
+      lumiera_fileheader_close (&header, LUMIERA_FILEHEADER_FLAG_CLEAN);
     }
 
   lumiera_file_delete (file);
@@ -80,12 +80,14 @@ TEST (acquire_wrongheader)
 
   LUMIERA_FILE_RDLOCK_SECTION (NOBUG_ON, file)
     {
-      lumiera_fileheader header = lumiera_fileheader_open (file, "BADH", sizeof (lumiera_fileheader));
+      lumiera_fileheader header = lumiera_fileheader_open (file, "BADH",
+                                                           sizeof (lumiera_fileheader),
+                                                           LUMIERA_FILEHEADER_FLAG_CLEAN, LUMIERA_FILEHEADER_FLAG_CLEAN);
 
       CHECK(!header.header);
       CHECK(lumiera_error() == LUMIERA_ERROR_FILEHEADER_HEADER);
 
-      lumiera_fileheader_close (&header);
+      lumiera_fileheader_close (&header, LUMIERA_FILEHEADER_FLAG_CLEAN);
     }
 
   lumiera_file_delete (file);
@@ -97,11 +99,13 @@ TEST (acquire_wrongheader)
 TEST (acquire_basic)
 {
   lumiera_backend_init ();
-  LumieraFile file = lumiera_file_new (",tmp-fileheader", LUMIERA_FILE_READONLY);
+  LumieraFile file = lumiera_file_new (",tmp-fileheader", LUMIERA_FILE_READWRITE);
 
   LUMIERA_FILE_RDLOCK_SECTION (NOBUG_ON, file)
     {
-      lumiera_fileheader header = lumiera_fileheader_open (file, "TEST", sizeof (lumiera_fileheader));
+      lumiera_fileheader header = lumiera_fileheader_open (file, "TEST",
+                                                           sizeof (lumiera_fileheader),
+                                                           LUMIERA_FILEHEADER_FLAG_CLEAN, LUMIERA_FILEHEADER_FLAG_CLEAN);
 
       CHECK(header.header);
       CHECK(!lumiera_error());
@@ -110,7 +114,34 @@ TEST (acquire_basic)
 
       ECHO ("fileheader: %s:", (char*)header.header);
 
-      lumiera_fileheader_close (&header);
+      lumiera_fileheader_close (&header, LUMIERA_FILEHEADER_FLAG_CLEAN);
+    }
+
+  lumiera_file_delete (file);
+  lumiera_backend_destroy ();
+
+}
+
+
+TEST (acquire_basic_readonly)
+{
+  lumiera_backend_init ();
+  LumieraFile file = lumiera_file_new (",tmp-fileheader", LUMIERA_FILE_READONLY);
+
+  LUMIERA_FILE_RDLOCK_SECTION (NOBUG_ON, file)
+    {
+      lumiera_fileheader header = lumiera_fileheader_open (file, "TEST",
+                                                           sizeof (lumiera_fileheader),
+                                                           LUMIERA_FILEHEADER_FLAG_CLEAN, NULL);
+
+      CHECK(header.header);
+      CHECK(!lumiera_error());
+
+      CHECK (lumiera_fileheader_version (&header) == 0);
+
+      ECHO ("fileheader: %s:", (char*)header.header);
+
+      lumiera_fileheader_close (&header, LUMIERA_FILEHEADER_FLAG_CLEAN);
     }
 
   lumiera_file_delete (file);