diff --git a/CHANGED b/CHANGED
index 65adca5e0..831e5ecbd 100644
--- a/CHANGED
+++ b/CHANGED
@@ -1,5 +1,6 @@
 # Add changes at the top of the list. Keep it in ASCII, and 80-char wide.
 # Do not insert empty lines here, update check depends on it.
+  - feature: limit reading/attr name length in featurelevel 6.0+ (Forum #97493)
   - feature: 49_SSCam: send recordings by telegram is integrated as well as 
                        sending snapshots
   - bugfix:  74_XiaomiBTLESens: fix Undefined subroutine
diff --git a/FHEM/01_FHEMWEB.pm b/FHEM/01_FHEMWEB.pm
index b29313e19..3eaba5cfb 100644
--- a/FHEM/01_FHEMWEB.pm
+++ b/FHEM/01_FHEMWEB.pm
@@ -4123,6 +4123,16 @@ FW_show($$)
         <br>
     </ul>
   </ul>
+
+  <a name="cmdshow"></a>
+  <h3>show</h3>
+  <ul>
+    <code>show [devspec]</code><br>
+    <br><br>
+    Show a temporary room with devices from &lt;devspec&gt;<br>
+    Note: this command is only available through the FHEMWEB interface
+  </ul>
+
 =end html
 
 =begin html_DE
@@ -4844,6 +4854,16 @@ FW_show($$)
         </ul></li>
 
     </ul>
+
+    <a name="cmdshow"></a>
+    <h3>show</h3>
+    <ul>
+      <code>show [devspec]</code><br>
+      <br><br>
+      Zeigt einen tempor&auml;ren Raum mit dem Inhalt der &lt;devspec&gt;<br>
+      Achtung: dieser Befehl steht nur &uuml;ber das FHEMWEB Interface zur
+      Verf&uuml;gung.
+    </ul>
   </ul>
 
 =end html_DE
diff --git a/FHEM/10_MQTT2_DEVICE.pm b/FHEM/10_MQTT2_DEVICE.pm
index e4c567107..7f104a6ae 100644
--- a/FHEM/10_MQTT2_DEVICE.pm
+++ b/FHEM/10_MQTT2_DEVICE.pm
@@ -391,7 +391,8 @@ MQTT2_DEVICE_Attr($$)
                  "%JSONMAP"=>""));
           return $ret if($ret);
         } else {
-          return "unsupported character in readingname $par2"
+          return "bad reading name $par2 ".
+                        "(contains not A-Za-z/\\d_\\.- or is too long)"
               if(!goodReadingName($par2));
         }
 
diff --git a/UPGRADE b/UPGRADE
index 37f201bb9..42858cba5 100644
--- a/UPGRADE
+++ b/UPGRADE
@@ -32,3 +32,7 @@ enable the old feature.
     fhemSVG:openautomation:default. NOTE: the old version may be needed for
     FLORRPLAN users
   - the default fhem.cfg does not contain a telnet definition
+
+- XXXX-XX-XX (6.0)
+  - attribute names can only consist of the character A-Za-z/\d_\.-
+  - the length of attribute and reading names must be 64 or less
diff --git a/fhem.pl b/fhem.pl
index ce764040f..6de9a13f8 100755
--- a/fhem.pl
+++ b/fhem.pl
@@ -2392,9 +2392,10 @@ CommandSetReading($$)
       ($err, @b) = ReplaceSetMagic($hash, 3, @a);
       delete $hash->{CL};
     }
-    return "WARNING: unsupported character in reading $b[1] ".
-           "(not A-Za-z/\\d_\\.-)" if(!goodReadingName($b[1]));
-    readingsSingleUpdate($defs{$sdev}, $b[1], $b[2], 1);
+    my $b1 = $b[1];
+    return "bad reading name $b1 (contains not A-Za-z/\\d_\\.- or is too long)"
+      if(!goodReadingName($b1));
+    readingsSingleUpdate($defs{$sdev}, $b1, $b[2], 1);
   }
   return join("\n", @rets);
 }
@@ -2830,12 +2831,15 @@ CommandAttr($$)
 
   return "Usage: attr [-a|-r] <name> <attrname> [<attrvalue>]\n$namedef"
            if(@a && @a < 2);
+  my $a1 = $a[1];
+  return "bad attribute name $a1 (contains not A-Za-z/\\d_\\.- or is too long)"
+           if($featurelevel > 5.9 && !goodReadingName($a1));
 
   my @rets;
-  foreach my $sdev (devspec2array($a[0], $a[1] && $a[1] eq "?" ? undef : $cl)) {
+  foreach my $sdev (devspec2array($a[0], $a1 && $a1 eq "?" ? undef : $cl)) {
 
     my $hash = $defs{$sdev};
-    my $attrName = $a[1];
+    my $attrName = $a1;
     my $attrVal = (defined($a[2]) ? $a[2] : 1);
     if(!defined($hash)) {
       push @rets, "Please define $sdev first" if($init_done);#define -ignoreErr
@@ -3045,8 +3049,8 @@ CommandSetstate($$)
         next;
       }
 
-      Log3 $d, 3, "WARNING: unsupported character in reading $sname ".
-             "(not A-Za-z/\\d_\\.-), notify the $d->{TYPE} module maintainer."
+      Log3 $d, 3,
+         "bad reading name $sname (contains not A-Za-z/\\d_\\.- or is too long)"
         if(!goodReadingName($sname));
 
       if(!defined($d->{READINGS}{$sname}) ||
@@ -5700,7 +5704,9 @@ sub
 goodReadingName($)
 {
   my ($name) = @_;
-  return ($name && ($name =~ m/^[a-z0-9._\-\/]+$/i || $name =~ m/^\./));
+  return undef if(!$name);
+  return undef if($featurelevel > 5.9 && length($name) > 64);
+  return ($name =~ m/^[a-z0-9._\-\/]+$/i || $name =~ m/^\./);
 }
 
 sub
@@ -5710,6 +5716,7 @@ makeReadingName($) # Convert non-valid characters to _
   $name = "UNDEFINED" if(!defined($name));
   return $name if($name =~ m/^\./);
   $name =~ s/[^a-z0-9._\-\/]/_/gi;
+  $name = substr($name, 0, 64) if($featurelevel > 5.9 && length($name) > 64);
   return $name;
 }