diff --git a/src/calibre/ebooks/metadata/tag_mapper.py b/src/calibre/ebooks/metadata/tag_mapper.py
new file mode 100644
index 0000000000..237848bb0f
--- /dev/null
+++ b/src/calibre/ebooks/metadata/tag_mapper.py
@@ -0,0 +1,53 @@
+#!/usr/bin/env python2
+# vim:fileencoding=utf-8
+# License: GPLv3 Copyright: 2015, Kovid Goyal <kovid at kovidgoyal.net>
+
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+import regex
+REGEX_FLAGS = regex.VERSION1 | regex.WORD | regex.FULLCASE | regex.IGNORECASE | regex.UNICODE
+
+
+def matcher(rule):
+    mt = rule['match_type']
+    if mt == 'one_of':
+        tags = {icu_lower(x.strip()) for x in rule['query'].split(',')}
+        return lambda x: x in tags
+
+    if mt == 'not_one_of':
+        tags = {icu_lower(x.strip()) for x in rule['query'].split(',')}
+        return lambda x: x not in tags
+
+    if mt == 'matches':
+        pat = regex.compile(rule['query'], flags=REGEX_FLAGS)
+        return lambda x: pat.match(x) is not None
+
+    if mt == 'not_matches':
+        pat = regex.compile(rule['query'], flags=REGEX_FLAGS)
+        return lambda x: pat.match(x) is None
+
+    return lambda x: False
+
+
+def apply_rules(tag, rules):
+    for rule, matches in rules:
+        ltag = icu_lower(tag)
+        if matches(ltag):
+            ac = rule['action']
+            if ac == 'remove':
+                return None
+            if ac == 'keep':
+                return tag
+            if ac == 'replace':
+                tag = regex.sub(rule['query'], rule['replace'], flags=REGEX_FLAGS)
+    return tag
+
+
+def map_tags(tags, rules=()):
+    if not tags:
+        return []
+    if not rules:
+        return list(tags)
+    rules = [(r, matcher(r)) for r in rules]
+    return [x for x in (apply_rules(t, rules) for t in tags) if x]
diff --git a/src/calibre/gui2/tag_mapper.py b/src/calibre/gui2/tag_mapper.py
index cdb8cfe0c2..3e010ce63d 100644
--- a/src/calibre/gui2/tag_mapper.py
+++ b/src/calibre/gui2/tag_mapper.py
@@ -14,6 +14,7 @@ from PyQt5.Qt import (
     QStaticText, Qt, QStyle, QToolButton, QInputDialog, QMenu
 )
 
+from calibre.ebooks.metadata.tag_mapper import map_tags
 from calibre.gui2 import error_dialog, elided_text, Application, question_dialog
 from calibre.gui2.widgets2 import Dialog
 from calibre.utils.config import JSONConfig
@@ -272,11 +273,43 @@ class Rules(QWidget):
             if 'action' in rule and 'match_type' in rule and 'query' in rule:
                 RuleItem(rule, self.rule_list)
 
+class Tester(Dialog):
+
+    def __init__(self, rules, parent=None):
+        self.rules = rules
+        Dialog.__init__(self, _('Test tag mapper rules'), 'test-tag-mapper-rules', parent=parent)
+
+    def setup_ui(self):
+        self.l = l = QVBoxLayout(self)
+        self.bb.setStandardButtons(self.bb.Close)
+        self.la = la = QLabel(_(
+            'Enter a comma separated list of &tags to test:'))
+        l.addWidget(la)
+        self.tags = t = QLineEdit(self)
+        la.setBuddy(t)
+        t.setPlaceholderText(_('Enter tags and click the Test button'))
+        self.h = h = QHBoxLayout()
+        l.addLayout(h)
+        h.addWidget(t)
+        self.test_button = b = QPushButton(_('&Test'), self)
+        b.clicked.connect(self.do_test)
+        h.addWidget(b)
+        self.result = la = QLabel(self)
+        la.setWordWrap(True)
+        l.addWidget(la)
+        l.addWidget(self.bb)
+
+    def do_test(self):
+        tags = [x.strip() for x in self.tags.text().split(',')]
+        tags = map_tags(tags, self.rules)
+        self.result.setText(_('<b>Resulting tags:</b> %s') % ', '.join(tags))
+
+
 class RulesDialog(Dialog):
 
     def __init__(self, parent=None):
         self.loaded_ruleset = None
-        Dialog.__init__(self, _('Edit tag mapper rules'), 'edit-tag-mapper-rules', parent=None)
+        Dialog.__init__(self, _('Edit tag mapper rules'), 'edit-tag-mapper-rules', parent=parent)
 
     def setup_ui(self):
         self.l = l = QVBoxLayout(self)
@@ -291,6 +324,8 @@ class RulesDialog(Dialog):
         self.load_menu = QMenu(self)
         b.setMenu(self.load_menu)
         self.build_load_menu()
+        self.test_button = b = self.bb.addButton(_('&Test rules'), self.bb.ActionRole)
+        b.clicked.connect(self.test_rules)
 
     @property
     def rules(self):
@@ -336,6 +371,9 @@ class RulesDialog(Dialog):
         del tag_maps[name]
         self.build_load_menu()
 
+    def test_rules(self):
+        Tester(self.rules, self).exec_()
+
 if __name__ == '__main__':
     app = Application([])
     d = RulesDialog()