diff --git a/tests/rules/common.py b/tests/rules/common.py
index cf5ff07..ade842e 100644
--- a/tests/rules/common.py
+++ b/tests/rules/common.py
@@ -18,7 +18,7 @@ import unittest
 
 import yaml
 
-from yamllint.config import parse_config
+from yamllint.config import YamlLintConfig
 from yamllint.errors import LintProblem
 from yamllint import lint
 
@@ -31,7 +31,7 @@ class RuleTestCase(unittest.TestCase):
             conf = yaml.safe_load(conf)
         conf = {'extends': 'default',
                 'rules': conf}
-        return parse_config(yaml.safe_dump(conf))
+        return YamlLintConfig(yaml.safe_dump(conf))
 
     def check(self, source, conf, **kwargs):
         expected_problems = []
diff --git a/tests/test_config.py b/tests/test_config.py
index 050530f..21d533d 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -14,56 +14,164 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-import os
 import unittest
 
 from yamllint import config
 
 
-class ConfigTestCase(unittest.TestCase):
-    def setUp(self):
-        self.base = config.parse_config_from_file(os.path.join(
-            os.path.dirname(os.path.dirname(os.path.realpath(__file__))),
-            'yamllint', 'conf', 'default.yml'))
+class SimpleConfigTestCase(unittest.TestCase):
+    def test_parse_config(self):
+        new = config.YamlLintConfig('rules:\n'
+                                    '  colons:\n'
+                                    '    max-spaces-before: 0\n'
+                                    '    max-spaces-after: 1\n')
 
+        self.assertEqual(list(new.rules.keys()), ['colons'])
+        self.assertEqual(new.rules['colons']['max-spaces-before'], 0)
+        self.assertEqual(new.rules['colons']['max-spaces-after'], 1)
+
+        self.assertEqual(len(new.enabled_rules()), 1)
+
+    def test_unknown_rule(self):
+        with self.assertRaisesRegexp(
+                config.YamlLintConfigError,
+                'invalid config: no such rule: "this-one-does-not-exist"'):
+            config.YamlLintConfig('rules:\n'
+                                  '  this-one-does-not-exist: {}\n')
+
+    def test_missing_option(self):
+        with self.assertRaisesRegexp(
+                config.YamlLintConfigError,
+                'invalid config: missing option "max-spaces-before" '
+                'for rule "colons"'):
+            config.YamlLintConfig('rules:\n'
+                                  '  colons:\n'
+                                  '    max-spaces-after: 1\n')
+
+    def test_unknown_option(self):
+        with self.assertRaisesRegexp(
+                config.YamlLintConfigError,
+                'invalid config: unknown option "abcdef" for rule "colons"'):
+            config.YamlLintConfig('rules:\n'
+                                  '  colons:\n'
+                                  '    max-spaces-before: 0\n'
+                                  '    max-spaces-after: 1\n'
+                                  '    abcdef: yes\n')
+
+
+class ExtendedConfigTestCase(unittest.TestCase):
+    def test_extend_add_rule(self):
+        old = config.YamlLintConfig('rules:\n'
+                                    '  colons:\n'
+                                    '    max-spaces-before: 0\n'
+                                    '    max-spaces-after: 1\n')
+        new = config.YamlLintConfig('rules:\n'
+                                    '  hyphens:\n'
+                                    '    max-spaces-after: 2\n')
+        new.extend(old)
+
+        self.assertEqual(sorted(new.rules.keys()), ['colons', 'hyphens'])
+        self.assertEqual(new.rules['colons']['max-spaces-before'], 0)
+        self.assertEqual(new.rules['colons']['max-spaces-after'], 1)
+        self.assertEqual(new.rules['hyphens']['max-spaces-after'], 2)
+
+        self.assertEqual(len(new.enabled_rules()), 2)
+
+    def test_extend_remove_rule(self):
+        old = config.YamlLintConfig('rules:\n'
+                                    '  colons:\n'
+                                    '    max-spaces-before: 0\n'
+                                    '    max-spaces-after: 1\n'
+                                    '  hyphens:\n'
+                                    '    max-spaces-after: 2\n')
+        new = config.YamlLintConfig('rules:\n'
+                                    '  colons: disable\n')
+        new.extend(old)
+
+        self.assertEqual(sorted(new.rules.keys()), ['colons', 'hyphens'])
+        self.assertEqual(new.rules['colons'], False)
+        self.assertEqual(new.rules['hyphens']['max-spaces-after'], 2)
+
+        self.assertEqual(len(new.enabled_rules()), 1)
+
+    def test_extend_edit_rule(self):
+        old = config.YamlLintConfig('rules:\n'
+                                    '  colons:\n'
+                                    '    max-spaces-before: 0\n'
+                                    '    max-spaces-after: 1\n'
+                                    '  hyphens:\n'
+                                    '    max-spaces-after: 2\n')
+        new = config.YamlLintConfig('rules:\n'
+                                    '  colons:\n'
+                                    '    max-spaces-before: 3\n'
+                                    '    max-spaces-after: 4\n')
+        new.extend(old)
+
+        self.assertEqual(sorted(new.rules.keys()), ['colons', 'hyphens'])
+        self.assertEqual(new.rules['colons']['max-spaces-before'], 3)
+        self.assertEqual(new.rules['colons']['max-spaces-after'], 4)
+        self.assertEqual(new.rules['hyphens']['max-spaces-after'], 2)
+
+        self.assertEqual(len(new.enabled_rules()), 2)
+
+    def test_extend_reenable_rule(self):
+        old = config.YamlLintConfig('rules:\n'
+                                    '  colons:\n'
+                                    '    max-spaces-before: 0\n'
+                                    '    max-spaces-after: 1\n'
+                                    '  hyphens: disable\n')
+        new = config.YamlLintConfig('rules:\n'
+                                    '  hyphens:\n'
+                                    '    max-spaces-after: 2\n')
+        new.extend(old)
+
+        self.assertEqual(sorted(new.rules.keys()), ['colons', 'hyphens'])
+        self.assertEqual(new.rules['colons']['max-spaces-before'], 0)
+        self.assertEqual(new.rules['colons']['max-spaces-after'], 1)
+        self.assertEqual(new.rules['hyphens']['max-spaces-after'], 2)
+
+        self.assertEqual(len(new.enabled_rules()), 2)
+
+
+class ExtendedLibraryConfigTestCase(unittest.TestCase):
     def test_extend_config_disable_rule(self):
-        new = config.parse_config('extends: default\n'
-                                  'rules:\n'
-                                  '  trailing-spaces: disable\n')
+        old = config.YamlLintConfig('extends: default')
+        new = config.YamlLintConfig('extends: default\n'
+                                    'rules:\n'
+                                    '  trailing-spaces: disable\n')
 
-        base = self.base.copy()
-        del base['trailing-spaces']
+        old.rules['trailing-spaces'] = False
 
-        self.assertEqual(sorted(new.keys()), sorted(base.keys()))
-        for rule in new:
-            self.assertEqual(new[rule], base[rule])
+        self.assertEqual(sorted(new.rules.keys()), sorted(old.rules.keys()))
+        for rule in new.rules:
+            self.assertEqual(new.rules[rule], old.rules[rule])
 
     def test_extend_config_override_whole_rule(self):
-        new = config.parse_config('extends: default\n'
-                                  'rules:\n'
-                                  '  empty-lines:\n'
-                                  '    max: 42\n'
-                                  '    max-start: 43\n'
-                                  '    max-end: 44\n')
-
-        base = self.base.copy()
-        base['empty-lines']['max'] = 42
-        base['empty-lines']['max-start'] = 43
-        base['empty-lines']['max-end'] = 44
-
-        self.assertEqual(sorted(new.keys()), sorted(base.keys()))
-        for rule in new:
-            self.assertEqual(new[rule], base[rule])
+        old = config.YamlLintConfig('extends: default')
+        new = config.YamlLintConfig('extends: default\n'
+                                    'rules:\n'
+                                    '  empty-lines:\n'
+                                    '    max: 42\n'
+                                    '    max-start: 43\n'
+                                    '    max-end: 44\n')
+
+        old.rules['empty-lines']['max'] = 42
+        old.rules['empty-lines']['max-start'] = 43
+        old.rules['empty-lines']['max-end'] = 44
+
+        self.assertEqual(sorted(new.rules.keys()), sorted(old.rules.keys()))
+        for rule in new.rules:
+            self.assertEqual(new.rules[rule], old.rules[rule])
 
     def test_extend_config_override_rule_partly(self):
-        new = config.parse_config('extends: default\n'
-                                  'rules:\n'
-                                  '  empty-lines:\n'
-                                  '    max-start: 42\n')
+        old = config.YamlLintConfig('extends: default')
+        new = config.YamlLintConfig('extends: default\n'
+                                    'rules:\n'
+                                    '  empty-lines:\n'
+                                    '    max-start: 42\n')
 
-        base = self.base.copy()
-        base['empty-lines']['max-start'] = 42
+        old.rules['empty-lines']['max-start'] = 42
 
-        self.assertEqual(sorted(new.keys()), sorted(base.keys()))
-        for rule in new:
-            self.assertEqual(new[rule], base[rule])
+        self.assertEqual(sorted(new.rules.keys()), sorted(old.rules.keys()))
+        for rule in new.rules:
+            self.assertEqual(new.rules[rule], old.rules[rule])
diff --git a/yamllint/__init__.py b/yamllint/__init__.py
index a8d2d2b..fbc3675 100644
--- a/yamllint/__init__.py
+++ b/yamllint/__init__.py
@@ -16,7 +16,6 @@
 
 import yaml
 
-from yamllint import config
 from yamllint.errors import LintProblem
 from yamllint import parser
 
@@ -32,7 +31,7 @@ __version__ = APP_VERSION
 
 
 def get_costemic_problems(buffer, conf):
-    rules = config.get_enabled_rules(conf)
+    rules = conf.enabled_rules()
 
     # Split token rules from line rules
     token_rules = [r for r in rules if r.TYPE == 'token']
@@ -45,7 +44,7 @@ def get_costemic_problems(buffer, conf):
     for elem in parser.token_or_line_generator(buffer):
         if isinstance(elem, parser.Token):
             for rule in token_rules:
-                rule_conf = conf[rule.ID]
+                rule_conf = conf.rules[rule.ID]
                 for problem in rule.check(rule_conf,
                                           elem.curr, elem.prev, elem.next,
                                           context[rule.ID]):
@@ -54,7 +53,7 @@ def get_costemic_problems(buffer, conf):
                     yield problem
         elif isinstance(elem, parser.Line):
             for rule in line_rules:
-                rule_conf = conf[rule.ID]
+                rule_conf = conf.rules[rule.ID]
                 for problem in rule.check(rule_conf, elem):
                     problem.rule = rule.ID
                     problem.level = rule_conf['level']
diff --git a/yamllint/cli.py b/yamllint/cli.py
index cbe3b8d..0dc8511 100644
--- a/yamllint/cli.py
+++ b/yamllint/cli.py
@@ -22,8 +22,7 @@ import sys
 import argparse
 
 from yamllint import APP_DESCRIPTION, APP_NAME, APP_VERSION
-from yamllint import config
-from yamllint.errors import YamlLintConfigError
+from yamllint.config import YamlLintConfig, YamlLintConfigError
 from yamllint import lint
 
 
@@ -82,11 +81,11 @@ def run(argv):
 
     try:
         if args.config_file is not None:
-            conf = config.parse_config_from_file(args.config_file)
+            conf = YamlLintConfig(file=args.config_file)
         elif os.path.isfile('.yamllint'):
-            conf = config.parse_config_from_file('.yamllint')
+            conf = YamlLintConfig(file='.yamllint')
         else:
-            conf = config.parse_config('extends: default')
+            conf = YamlLintConfig('extends: default')
     except YamlLintConfigError as e:
         print(e, file=sys.stderr)
         sys.exit(-1)
diff --git a/yamllint/config.py b/yamllint/config.py
index fc9d4fb..0814dfd 100644
--- a/yamllint/config.py
+++ b/yamllint/config.py
@@ -19,95 +19,116 @@ import os.path
 import yaml
 
 import yamllint.rules
-from yamllint.errors import YamlLintConfigError
 
 
-def get_extended_conf(name):
-    # Is it a standard conf shipped with yamllint...
-    if '/' not in name:
-        std_conf = os.path.join(os.path.dirname(os.path.realpath(__file__)),
-                                'conf', name + '.yml')
-
-        if os.path.isfile(std_conf):
-            return std_conf
+class YamlLintConfigError(Exception):
+    pass
 
-    # or a custom conf on filesystem?
-    return name
 
+class YamlLintConfig(object):
+    def __init__(self, content=None, file=None):
+        assert (content is None) ^ (file is None)
 
-def extend_config(content):
-    try:
-        conf = yaml.safe_load(content)
+        if file is not None:
+            with open(file) as f:
+                content = f.read()
 
-        if 'rules' not in conf:
-            conf['rules'] = {}
+        self.parse(content)
+        self.validate()
 
-        # Does this conf override another conf that we need to load?
-        if 'extends' in conf:
-            base = parse_config_from_file(get_extended_conf(conf['extends']))
+    def enabled_rules(self):
+        return [yamllint.rules.get(id) for id, val in self.rules.items()
+                if val is not False]
 
-            for rule in conf['rules']:
-                if type(conf['rules'][rule]) == dict and rule in base:
-                    base[rule].update(conf['rules'][rule])
-                else:
-                    base[rule] = conf['rules'][rule]
-            conf['rules'] = base
+    def extend(self, base_config):
+        assert isinstance(base_config, YamlLintConfig)
 
-        return conf
-    except Exception as e:
-        raise YamlLintConfigError('invalid config: %s' % e)
+        for rule in self.rules:
+            if (type(self.rules[rule]) == dict and
+                    rule in base_config.rules and
+                    base_config.rules[rule] is not False):
+                base_config.rules[rule].update(self.rules[rule])
+            else:
+                base_config.rules[rule] = self.rules[rule]
 
+        self.rules = base_config.rules
 
-def parse_config(content):
-    conf = extend_config(content)
-    rules = {}
-
-    for id in conf['rules']:
+    def parse(self, raw_content):
         try:
-            rule = yamllint.rules.get(id)
+            conf = yaml.safe_load(raw_content)
         except Exception as e:
             raise YamlLintConfigError('invalid config: %s' % e)
 
-        if conf['rules'][id] == 'disable':
-            continue
+        self.rules = conf.get('rules', {})
 
-        rules[id] = {'level': 'error'}
-        if type(conf['rules'][id]) == dict:
-            if 'level' in conf['rules'][id]:
-                if conf['rules'][id]['level'] not in ('error', 'warning'):
+        # Does this conf override another conf that we need to load?
+        if 'extends' in conf:
+            path = get_extended_config_file(conf['extends'])
+            base = YamlLintConfig(file=path)
+            try:
+                self.extend(base)
+            except Exception as e:
+                raise YamlLintConfigError('invalid config: %s' % e)
+
+    def validate(self):
+        for id in self.rules:
+            try:
+                rule = yamllint.rules.get(id)
+            except Exception as e:
+                raise YamlLintConfigError('invalid config: %s' % e)
+
+            self.rules[id] = validate_rule_conf(rule, self.rules[id])
+
+
+def validate_rule_conf(rule, conf):
+    if conf is False or conf == 'disable':
+        return False
+
+    if type(conf) == dict:
+        if 'level' not in conf:
+            conf['level'] = 'error'
+        elif conf['level'] not in ('error', 'warning'):
+            raise YamlLintConfigError(
+                'invalid config: level should be "error" or "warning"')
+
+        options = getattr(rule, 'CONF', {})
+        for optkey in conf:
+            if optkey == 'level':
+                continue
+            if optkey not in options:
+                raise YamlLintConfigError(
+                    'invalid config: unknown option "%s" for rule "%s"' %
+                    (optkey, rule.ID))
+            if type(options[optkey]) == tuple:
+                if conf[optkey] not in options[optkey]:
                     raise YamlLintConfigError(
-                        'invalid config: level should be "error" or "warning"')
-                rules[id]['level'] = conf['rules'][id]['level']
-
-            options = getattr(rule, 'CONF', {})
-            for optkey in conf['rules'][id]:
-                if optkey == 'level':
-                    continue
-                if optkey not in options:
+                        'invalid config: option "%s" of "%s" should be in %s'
+                        % (optkey, rule.ID, options[optkey]))
+            else:
+                if type(conf[optkey]) != options[optkey]:
                     raise YamlLintConfigError(
-                        'invalid config: unknown option "%s" for rule "%s"' %
-                        (optkey, id))
-                if type(options[optkey]) == tuple:
-                    if conf['rules'][id][optkey] not in options[optkey]:
-                        raise YamlLintConfigError(
-                            ('invalid config: option "%s" of "%s" should be '
-                             'in %s') % (optkey, id, options[optkey]))
-                else:
-                    if type(conf['rules'][id][optkey]) != options[optkey]:
-                        raise YamlLintConfigError(
-                            ('invalid config: option "%s" of "%s" should be '
-                             '%s' % (optkey, id, options[optkey].__name__)))
-                rules[id][optkey] = conf['rules'][id][optkey]
-        else:
-            raise YamlLintConfigError(('invalid config: rule "%s": should be '
-                                       'either "disable" or a dict') % id)
-    return rules
-
-
-def parse_config_from_file(path):
-    with open(path) as f:
-        return parse_config(f.read())
-
-
-def get_enabled_rules(conf):
-    return [yamllint.rules.get(r) for r in conf.keys() if conf[r] is not False]
+                        'invalid config: option "%s" of "%s" should be %s'
+                        % (optkey, rule.ID, options[optkey].__name__))
+        for optkey in options:
+            if optkey not in conf:
+                raise YamlLintConfigError(
+                    'invalid config: missing option "%s" for rule "%s"' %
+                    (optkey, rule.ID))
+    else:
+        raise YamlLintConfigError(('invalid config: rule "%s": should be '
+                                   'either "disable" or a dict') % rule.ID)
+
+    return conf
+
+
+def get_extended_config_file(name):
+    # Is it a standard conf shipped with yamllint...
+    if '/' not in name:
+        std_conf = os.path.join(os.path.dirname(os.path.realpath(__file__)),
+                                'conf', name + '.yml')
+
+        if os.path.isfile(std_conf):
+            return std_conf
+
+    # or a custom conf on filesystem?
+    return name