--- a/CHANGES.txt	Wed Jan 01 01:02:09 2025 -0500
+++ b/CHANGES.txt	Wed Jan 01 02:06:00 2025 -0500
@@ -59,9 +59,7 @@
 - fixed a crash with roundup-admin perftest password when rounds not set
   on command line. (John Rouillard)
 - issue2551374 - Add error handling for filter expressions. Filter
-  expression errors are now reported. The UI needs some work but
-  even the current code is helpful when debugging filter
-  expressions. (John Rouillard)
+  expression errors are now reported. (John Rouillard)
 
 Features:
 

--- a/doc/user_guide.txt	Wed Jan 01 01:02:09 2025 -0500
+++ b/doc/user_guide.txt	Wed Jan 01 02:06:00 2025 -0500
@@ -491,12 +491,45 @@
 clicking on the ``(expr)`` link, which makes creating these
 expressions a bit easier.
 
-Note that errors in your expression (e.g. a missing operand) are
-silently ignored and a fallback search is conducted. This is
-`considered a bug <https://issues.roundup-tracker.org/issue2551374>`_
-and will hopefully be fixed in the future. But at least you can use
-this info to understand the search syntax in the URL if you see
-something strange.
+If your expression has an error, you will be returned to the search
+page and an error will be reported. For example using the expression
+``1, -3`` to search the nosy property of an issue generates the
+following error::
+
+   There was an error searching issue by nosy using: [1, -3]. The
+   operator -3 (and) at position 2 has too few arguments.
+
+The error message gives you the problem element (``-3``), it's meaning
+(``and``) and its position: the second element. The problem was caused
+because ``and`` requires two arguments, but only one argument (``1``)
+was given.
+
+Another error message::
+
+  There was an error searching issue by status using: [1, 2, -3,
+  -3]. The operator -3 (and) at position 4 has too few arguments.
+
+reports that the second ``-3`` in the 4th position is the problem
+operator. Note that this search expression will never return any
+values. This is because ``status`` is a single value (link) type
+property. It can't have the values ``1`` and ``2``, so the expression
+``1,2,-3`` will never return an issue.
+
+In the examples above, the error was caused by not having enough
+arguments. However you can also have too many arguments. An example of
+this type of message is::
+
+  There was an error searching issue by nosy using: [4, 5, 1, 2, -3,
+  -3]. There are too many arguments for the existing operators. The
+  values on the stack are: [Value 4, (Value 5 AND (Value 1 AND Value
+  2))]
+
+This message gives you the expression as far as it was able to compose
+it, but value 1 is not combined with the rest of the expression. So
+another binary operator is needed to complete the expression.
+
+If you have multiple incorrect expressions in your search, only one
+expression will be reported each time you submit the search.
 
 Using the Classhelper
 ---------------------

--- a/roundup/cgi/client.py	Wed Jan 01 01:02:09 2025 -0500
+++ b/roundup/cgi/client.py	Wed Jan 01 02:06:00 2025 -0500
@@ -2232,7 +2232,8 @@
                 result = self.renderError(e.args[0])
             except ExpressionError as e:
                 self.add_error_message(str(e))
-                result = self.renderError(str(e))
+                self.template = "search"
+                self.write_html(self.renderContext())
 
             if 'Content-Type' not in self.additional_headers:
                 self.additional_headers['Content-Type'] = pt.content_type

--- a/test/test_liveserver.py	Wed Jan 01 01:02:09 2025 -0500
+++ b/test/test_liveserver.py	Wed Jan 01 02:06:00 2025 -0500
@@ -380,7 +380,7 @@
                       '[-2]. The operator -2 (not) at position 1 has '
                       'too few arguments.',
                       f.text)
-        self.assertEqual(f.status_code, 400)
+        self.assertEqual(f.status_code, 200)
 
     def test_broken_multiink_query(self):
         # query multilink item
@@ -398,7 +398,7 @@
                       '[-3]. The operator -3 (and) at position 1 has '
                       'too few arguments.',
                       f.text)
-        self.assertEqual(f.status_code, 400)
+        self.assertEqual(f.status_code, 200)
 
     def test_start_page(self):
         """ simple test that verifies that the server can serve a start page.