diff --git a/.flake8 b/.flake8
index 7163b1e..4af900b 100644
--- a/.flake8
+++ b/.flake8
@@ -68,6 +68,7 @@ ignore =
     WPS336, # WPS336 Found explicit string concatenation
     WPS338, # WPS338 Found incorrect order of methods in a class
     WPS360, # WPS360 Found an unnecessary use of a raw string
+    WPS402, # WPS402 Found `noqa` comments overuse: 12
     WPS420, # WPS420 Found wrong keyword: pass
     WPS442, # WPS442 Found outer scope names shadowing:
     WPS600, # WPS600 Found subclassing a builtin: list
@@ -82,6 +83,9 @@ per-file-ignores =
     transtool/report/error.py: WPS420, WPS604,
     transtool/report/warn.py: WPS420, WPS604,
 
+	# WPS437 Found protected attribute usage
+	transtool/report/group.py: WPS437,
+
     # WPS230 Found too many public instance attributes
     transtool/config/config.py: WPS230,
 
@@ -130,12 +134,12 @@ per-file-ignores =
     # WPS214 Found too many methods
     # WPS323 Found `%` string formatting
     # WPS432 Found magic number
+    # WPS437 Found protected attribute usage
     # WPS609 Found direct magic attribute usage: __abstractmethods__
-    tests/*: S311, WPS323, WPS214, WPS432, WPS609, WPS118,
+    tests/*: S311, WPS323, WPS214, WPS432, WPS609, WPS118, WPS437,
 
     # WPS431 Found nested class: FakeArgs
-    # WPS437 Found protected attribute usage: _set_on_off_option
-    tests/report/test_config_builder.py: WPS431, WPS437,
+    tests/report/test_config_builder.py: WPS431,
 
     # WPS430 Found nested function: log_abort_side_effect
     # S311 Standard pseudo-random generators are not suitable for security/cryptographic purposes.
diff --git a/docs/CHANGES.md b/docs/CHANGES.md
index c497a84..f398363 100644
--- a/docs/CHANGES.md
+++ b/docs/CHANGES.md
@@ -6,6 +6,10 @@
 
 # Changelog #
 
+* v2.2.0 (2021-08-11)
+  * Added ability to specify checks to run with `--checks` option.
+  * Added more unit tests.
+
 * v2.1.0 (2021-08-06)
   * Rebranded and renamed project to `trans-tool`.
   * Fixed config loader not handling Checks' sections properly.
diff --git a/docs/config.md b/docs/config.md
index 2737913..8cf1e19 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -10,7 +10,7 @@
 * [« Documentation table of contents](README.md)
 * **Configuration**
   * [Config file](#config-file)
-  * [Syntax file](#syntax)
+  * [Syntax](#syntax)
   * [Structure](#structure)
     * [The [trans-tool] section](#trans-tool-section)
 
@@ -27,7 +27,7 @@ any text editor. Please see commented [config.ini](../config.ini) for example co
 
 You should be using standard `UTF-8` encoding for your configuration file.
 
-## Syntax ##
+# Syntax #
 
 Configuration file is separated into sections. Each section starts with section header put in separate line between square brackets,
 followed by section related configuration items. Items are usually in `key = value` form. All keys are always lower-cased, and for
@@ -99,6 +99,7 @@ The following elements are supported in `[trans-tool]` section
 
 | Key       | CLI switch    | Argument type | Default | Description |
 |-----------|---------------|---------------|---------|-------------|
+| checks    | `--checks`    | List of strings | `[ Brackets, ... ]` | List of Checks IDs to be used for content validation. |
 | comment   | `--comment`   | String        | `#`     | TODO |
 | separator | `--separator` | String        | `=`     | TODO |
 | quiet     | `--quiet`     | Boolean       | `false` | Quiet mode. If enabled, all but fatal errors are muted. |
diff --git a/requirements3.txt b/requirements3.txt
new file mode 100644
index 0000000..745be45
--- /dev/null
+++ b/requirements3.txt
@@ -0,0 +1,6 @@
+argparse
+wemake-python-styleguide
+pytest
+wheel
+setuptools
+twine
diff --git a/setup.py b/setup.py
index baea613..696d0c5 100755
--- a/setup.py
+++ b/setup.py
@@ -23,6 +23,8 @@
 
 with open('README.md', 'r') as fh:
     readme = fh.read()
+    readme.replace('![trans-tool logo](artwork/trans-tool-logo.png)',
+                   'https://raw.githubusercontent.com/MarcinOrlowski/trans-tool/master/artwork/trans-tool-logo.png', 1)
 
 setup(
     name = Const.APP_NAME,
diff --git a/tests/checks/checks_test_case.py b/tests/checks/checks_test_case.py
index 74a02c6..0247b42 100644
--- a/tests/checks/checks_test_case.py
+++ b/tests/checks/checks_test_case.py
@@ -104,7 +104,7 @@ def check_skipping_of_dangling_keys(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        trans_keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        trans_keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         # have less keys for reference file
         upper_bound = 10
diff --git a/tests/checks/test_dangling_keys.py b/tests/checks/test_dangling_keys.py
index a4995d6..1256a7e 100644
--- a/tests/checks/test_dangling_keys.py
+++ b/tests/checks/test_dangling_keys.py
@@ -27,7 +27,7 @@ def test_translation_no_faults(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
         ref_file = self.build_prepfile(keys)
         trans_file = self.build_prepfile(keys)
         self.check(trans_file, ref_file)
@@ -36,7 +36,7 @@ def test_translation_with_faults(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        trans_keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        trans_keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         # have less keys for reference file
         upper_bound = 10
diff --git a/tests/checks/test_empty_translations.py b/tests/checks/test_empty_translations.py
index 48e6a65..686c8bd 100644
--- a/tests/checks/test_empty_translations.py
+++ b/tests/checks/test_empty_translations.py
@@ -28,7 +28,7 @@ def test_no_faults(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
         ref_file = self.build_prepfile(keys)
         trans_file = self.build_prepfile(keys)
         self.check(trans_file, ref_file)
@@ -40,7 +40,7 @@ def test_if_both_are_empty(self) -> None:
         cnt_min = 10
         cnt_max = 20
         key_cnt = random.randint(cnt_min, cnt_max)
-        keys = [self.get_random_string('key_') for _ in range(key_cnt)]
+        keys = [self.get_random_string('key') for _ in range(key_cnt)]
         ref_file = self.build_prepfile(keys)
         trans_file = self.build_prepfile(keys)
 
@@ -72,7 +72,7 @@ def test_translation_with_dangling_keys(self) -> None:
         cnt_min = 10
         cnt_max = 20
         key_cnt = random.randint(cnt_min, cnt_max)
-        keys = [self.get_random_string('key_') for _ in range(key_cnt)]
+        keys = [self.get_random_string('key') for _ in range(key_cnt)]
         ref_file = self.build_prepfile(keys)
         trans_file = self.build_prepfile(keys)
 
@@ -100,7 +100,7 @@ def test_translation_with_faults(self) -> None:
         cnt_min = 10
         cnt_max = 20
         key_cnt = random.randint(cnt_min, cnt_max)
-        keys = [self.get_random_string('key_') for _ in range(key_cnt)]
+        keys = [self.get_random_string('key') for _ in range(key_cnt)]
 
         ref_file = self.build_prepfile(keys)
         trans_file = self.build_prepfile(keys)
diff --git a/tests/checks/test_missing_translations.py b/tests/checks/test_missing_translations.py
index 94e467c..3ec5c78 100644
--- a/tests/checks/test_missing_translations.py
+++ b/tests/checks/test_missing_translations.py
@@ -28,7 +28,7 @@ def test_no_faults(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
         ref_file = self.build_prepfile(keys)
         trans_file = self.build_prepfile(keys)
         self.check(trans_file, ref_file)
@@ -42,7 +42,7 @@ def test_translation_with_keys_in_comments(self) -> None:
         # Generate some keys for reference file.
         cnt_min = 10
         cnt_max = 15
-        ref_keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        ref_keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         # have less keys for translation file
         how_many_less = random.randint(1, cnt_min - 1)
@@ -58,7 +58,7 @@ def test_translation_with_keys_in_comments(self) -> None:
             if random.randint(0, 1) == 0:
                 comment = Comment.get_commented_out_key_comment(self.config, key)
             else:
-                val = self.get_random_string('translation_')
+                val = self.get_random_string('translation')
                 comment = Comment.get_commented_out_key_comment(self.config, key, val)
             trans_file.append(comment)
 
@@ -74,7 +74,7 @@ def test_translation_with_faults(self) -> None:
         # generate some keys for reference file
         cnt_min = 20
         cnt_max = 40
-        ref_keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        ref_keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         # have less keys for translation file
         how_many_less = random.randint(1, cnt_min - 1)
diff --git a/tests/checks/test_punctuation.py b/tests/checks/test_punctuation.py
index befbd5f..3dbe6b1 100644
--- a/tests/checks/test_punctuation.py
+++ b/tests/checks/test_punctuation.py
@@ -29,7 +29,7 @@ def test_no_faults(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         marks = self.checker.config['chars']
         punct_idx = 0
@@ -48,7 +48,7 @@ def test_with_faults(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         marks = self.checker.config['chars']
         punct_idx = 0
diff --git a/tests/checks/test_starts_with_the_same_case.py b/tests/checks/test_starts_with_the_same_case.py
index 8c51d62..91904f8 100644
--- a/tests/checks/test_starts_with_the_same_case.py
+++ b/tests/checks/test_starts_with_the_same_case.py
@@ -29,7 +29,7 @@ def get_checker(self, config: Union[Dict, None] = None) -> Check:
     def test_no_faults(self) -> None:
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         ref_file = PropFile(self.config)
         trans_file = PropFile(self.config)
@@ -43,7 +43,7 @@ def test_no_faults(self) -> None:
     def test_with_faults(self) -> None:
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         expected_faults = 0
 
@@ -68,7 +68,7 @@ def _do_scan_test(self, tests: List[Tuple[str, str]], exp_warnings = 0):
         for ref_value, trans_value in tests:
             ref_file = PropFile(self.config)
             trans_file = PropFile(self.config)
-            key = self.get_random_string('key_')
+            key = self.get_random_string('key')
             ref_file.append(Translation(key, ref_value))
             trans_file.append(Translation(key, trans_value))
             self.check(trans_file, ref_file, exp_warnings = exp_warnings)
@@ -144,7 +144,7 @@ def test_skipping_of_entry_items(self) -> None:
         # generate some keys for translation file
         cnt_min = 20
         cnt_max = 40
-        keys = [self.get_random_string('key_') for _ in range(random.randint(cnt_min, cnt_max))]
+        keys = [self.get_random_string('key') for _ in range(random.randint(cnt_min, cnt_max))]
 
         ref_file = self.build_prepfile(keys, lower = True)
         trans_file = self.build_prepfile(keys, lower = True)
diff --git a/tests/checks/test_substitutions.py b/tests/checks/test_substitutions.py
new file mode 100644
index 0000000..bb95cfc
--- /dev/null
+++ b/tests/checks/test_substitutions.py
@@ -0,0 +1,80 @@
+"""
+# trans-tool
+# The translation files checker and syncing tool.
+#
+# Copyright ©2021 Marcin Orlowski <mail [@] MarcinOrlowski.com>
+# https://github.com/MarcinOrlowski/trans-tool/
+#
+"""
+from typing import Dict, Union, List
+
+from transtool.checks.substitutions import Substitutions
+from transtool.decorators.overrides import overrides
+from transtool.prop.file import PropFile
+from transtool.prop.items import Comment, Translation
+from tests.checks.checks_test_case import ChecksTestCase
+
+
+class SubstitutionsTests(ChecksTestCase):
+
+    @overrides(ChecksTestCase)
+    def get_checker(self, config: Union[Dict, None] = None) -> Substitutions:
+        return Substitutions(config)
+
+    # #################################################################################################
+
+    def _get_valid_strings(self) -> List[str]:
+        return [
+            'Foo. Bar. All is fin5e!',
+            'Foo!',
+        ]
+
+    def _get_faulty_strings(self) -> List[str]:
+        return [
+            'Triple dots...',
+            'Ough!!!',
+        ]
+
+    def test_translation_no_faults(self) -> None:
+        for test in self._get_valid_strings():
+            self.check_single_file(Translation('key', test))
+
+    def test_empty_translation(self) -> None:
+        self.check(PropFile(self.config))
+
+    # #################################################################################################
+
+    def test_comment_no_faults(self) -> None:
+        for test in self._get_valid_strings():
+            self.check_single_file(Comment(test))
+
+    def test_comment_with_faults(self) -> None:
+        faults = self._get_faulty_strings()
+
+        for fault in faults:
+            # We should see no issues if comment scanning is disabled.
+            self.checker.config['comments'] = False
+            self.check_single_file(Comment(fault))
+
+            # And some warnings when comment scanning in enabled.
+            self.checker.config['comments'] = True
+            self.check_single_file(Comment(fault), exp_warnings = 1)
+
+    # #################################################################################################
+
+    def test_fail_with_error_flag(self) -> None:
+        """
+        Ensures FLAG_FAIL_WITH_ERROR flag aborts scanning and returns error while
+        FLAG_DEFAULT yields warning.
+        """
+        cfg = {
+            'regexp': r'([\.]{3})',
+            'replace': '…',
+        }
+        self.checker.config['map'] = [cfg]
+
+        cfg['flag'] = Substitutions.FLAG_DEFAULT
+        self.check_single_file(Translation('key', 'Triple dots...'), exp_warnings = 1)
+
+        cfg['flag'] = Substitutions.FLAG_FAIL_WITH_ERROR
+        self.check_single_file(Translation('key', 'Triple dots...'), exp_errors = 1)
diff --git a/tests/checks/test_white_chars_before_linefeed.py b/tests/checks/test_white_chars_before_linefeed.py
index fc3cddd..93f64a3 100644
--- a/tests/checks/test_white_chars_before_linefeed.py
+++ b/tests/checks/test_white_chars_before_linefeed.py
@@ -28,7 +28,7 @@ def test_translation_no_faults(self) -> None:
         self.check_single_file(Translation('key', r'This is\nall\nOK'))
 
     def test_translation_string_too_short(self) -> None:
-        # Checks behavior when the string is too short to fit space and litera,
+        # Checks behavior when the string is too short to fit space and literals,
         self.check_single_file(Translation('key', r' X'))
         self.check_single_file(Translation('key', r'\n'))
 
diff --git a/tests/config/test_config.py b/tests/config/test_config.py
new file mode 100644
index 0000000..8cdd993
--- /dev/null
+++ b/tests/config/test_config.py
@@ -0,0 +1,59 @@
+"""
+# trans-tool
+# The translation files checker and syncing tool.
+#
+# Copyright ©2021 Marcin Orlowski <mail [@] MarcinOrlowski.com>
+# https://github.com/MarcinOrlowski/trans-tool/
+#
+"""
+
+import random
+
+from tests.test_case import TestCase
+from transtool.config.config import Config
+
+
+class TestConfig(TestCase):
+
+    def test_set_checker_config(self) -> None:
+        config = Config()
+        checker_id = self.get_random_string('checker_id')
+        checker_config = {}
+        max_items = 10
+        for idx in range(random.randint(1, max_items)):
+            checker_config[self.get_random_string(f'key{idx}')] = self.get_random_string(f'val{idx}')
+        config.set_checker_config(checker_id, checker_config)
+
+        self.assertIn(checker_id, config.checks)
+        self.assertEqual(len(checker_config), len(config.checks[checker_id]))
+        for key, val in checker_config.items():
+            self.assertIn(key, config.checks[checker_id])
+            self.assertEqual(val, config.checks[checker_id][key])
+
+    def test_set_checker_config_invalid_type(self) -> None:
+        config = Config()
+        checker_id = self.get_random_string('checker_id')
+        with self.assertRaises(TypeError):
+            # noinspection PyTypeChecker
+            config.set_checker_config(checker_id, False)  # noqa: WPS425
+
+    def test_get_checker_config(self) -> None:
+        config = Config()
+        checker_id = self.get_random_string('checker_id')
+        checker_config = {}
+        max_items = 10
+        for idx in range(random.randint(1, max_items)):
+            checker_config[self.get_random_string(f'key{idx}')] = self.get_random_string(f'val{idx}')
+        config.set_checker_config(checker_id, checker_config)
+
+        read_config = config.get_checker_config(checker_id)
+        self.assertEqual(len(checker_config), len(read_config))
+        for key, val in checker_config.items():
+            self.assertIn(key, read_config)
+            self.assertEqual(val, read_config[key])
+
+    def test_get_checker_config_no_entry(self) -> None:
+        config = Config()
+        checker_id = self.get_random_string('checker_id')
+        with self.assertRaises(KeyError):
+            config.get_checker_config(checker_id)
diff --git a/tests/config/test_config_builder.py b/tests/config/test_config_builder.py
index c34cb08..a12c109 100644
--- a/tests/config/test_config_builder.py
+++ b/tests/config/test_config_builder.py
@@ -44,6 +44,9 @@ def __init__(self):
             self.__setattr__(option_name, False)
             self.__setattr__(f'no_{option_name}', False)
 
+        self.checkers = []
+        self.checks = {}
+
 
 class TestConfigBuilder(TestCase):
 
@@ -53,12 +56,10 @@ def test_fake_args_matches_config(self) -> None:
         """
         fake_args = FakeArgs()
         config = Config()
-        for key, val in config.__dict__.items():
+        for key in config.__dict__:
             # Let's skip Checks' info.
-            if isinstance(val, dict):
-                continue
-
-            self.assertIn(key, fake_args.__dict__, f'FakeArgs lacks "{key}" key."')
+            if key not in {'checks'}:  # noqa: WPS525
+                self.assertIn(key, fake_args.__dict__, f'FakeArgs lacks "{key}" key."')
 
     def test_fake_args_matches_argparse(self) -> None:
         """
@@ -70,7 +71,8 @@ def test_fake_args_matches_argparse(self) -> None:
         sys.argv[1:] = []  # noqa: WPS362
         args = ConfigBuilder._parse_args()
         for key in fake_args.__dict__:
-            self.assertIn(key, args)
+            if key not in {'checks'}:  # noqa: WPS525
+                self.assertIn(key, args)
 
     # #################################################################################################
 
@@ -265,7 +267,7 @@ def test_add_file_suffix_missing_suffix(self) -> None:
         dests = copy.copy(srcs)
         # WHEN we process it
         ConfigBuilder._add_file_suffix(config, dests)
-        # THEN all file names should have file suffix appened.
+        # THEN all file names should have file suffix appended.
         for idx, src in enumerate(srcs):
             self.assertEqual(f'{str(src)}{config.file_suffix}', str(dests[idx]))
 
@@ -378,6 +380,18 @@ def test_validate_args_invalid_comment_marker(self, log_e_mock: Mock) -> None:
 
     # #################################################################################################
 
+    def test_get_checkers_from_args(self) -> None:
+        config = Config()
+
+        # Pass no args for parsing (this is legit as we have config file that can provide what's needed).
+        sys.argv[1:] = []  # noqa: WPS362
+        args = ConfigBuilder._parse_args()
+        for key in config.__dict__:
+            if key not in {'checks'}:  # noqa: WPS525
+                self.assertIn(key, args)
+
+    # #################################################################################################
+
     def test_parse_args_returns_all_keys(self) -> None:
         """
         Checks if argparse returned dict contains all the keys we expect to be present while building
@@ -389,7 +403,8 @@ def test_parse_args_returns_all_keys(self) -> None:
         sys.argv[1:] = []  # noqa: WPS362
         args = ConfigBuilder._parse_args()
         for key in config.__dict__:
-            self.assertIn(key, args)
+            if key not in {'checks'}:  # noqa: WPS525
+                self.assertIn(key, args)
 
     def test_parse_args_returns_no_more_keys(self) -> None:
         """
@@ -410,6 +425,7 @@ def test_parse_args_returns_no_more_keys(self) -> None:
         # FIXME: this should not be hardcoded here!
         del args['show_version']
         del args['config_dump']
+        del args['checkers']
 
         for key in args:
             # Ensure key args returns is what is present in Config as well.
@@ -423,7 +439,7 @@ def test_build(self) -> None:
         args = self._generate_fake_args(languages)
 
         config = Config()
-        file = self.get_random_string('file_')
+        file = self.get_random_string('file')
         config.files.append(file)
 
         # Pass no args for parsing (this is legit as we have config file that can provide what's needed).
@@ -433,7 +449,7 @@ def test_build(self) -> None:
 
             ConfigBuilder.build(config)
 
-            # TODO: make comparision more detailed; add test for langs as well
+            # TODO: make comparison more detailed; add test for langs as well
             self.assertEqual(len(config.files), len(config.files))
             for idx, def_file in enumerate(config.files):
                 self.assertEqual(def_file, config.files[idx])
diff --git a/tests/prop/test_comment.py b/tests/prop/test_comment.py
index 685a265..891b894 100644
--- a/tests/prop/test_comment.py
+++ b/tests/prop/test_comment.py
@@ -33,7 +33,7 @@ def test_without_marker(self) -> None:
         Checks if constructing Comment without valid marker in passed value
         would automatically add such marker.
         """
-        val = self.get_random_string('no_maker_')
+        val = self.get_random_string('no_maker')
         # No valid comment marker
         comment = Comment(val)
         self.assertEqual(f'{Config.ALLOWED_COMMENT_MARKERS[0]} {val}', comment.to_string())
diff --git a/tests/prop/test_file.py b/tests/prop/test_file.py
index 62045ac..f50de5c 100644
--- a/tests/prop/test_file.py
+++ b/tests/prop/test_file.py
@@ -11,6 +11,7 @@
 from pathlib import Path
 from unittest.mock import Mock, mock_open, patch
 
+from transtool.config.builder import ConfigBuilder
 from transtool.config.config import Config
 from transtool.prop.file import PropFile
 from transtool.prop.items import Blank, Comment, PropItem, Translation
@@ -31,11 +32,11 @@ def _generate_propfile_with_content(self, config: Config) -> PropFile:
         new_items = 50
         for new_item_cls in random.choices(item_types, item_weights, k = new_items):
             if issubclass(new_item_cls, Translation):
-                key = self.get_random_string('key_')
-                val = self.get_random_string('ref_val_')
+                key = self.get_random_string('key')
+                val = self.get_random_string('ref_val')
                 propfile.append(Translation(key, val))
             elif issubclass(new_item_cls, Comment):
-                propfile.append(Comment(self.get_random_string('comment_')))
+                propfile.append(Comment(self.get_random_string('comment')))
             elif issubclass(new_item_cls, Blank):
                 propfile.append(Blank())
             else:
@@ -57,6 +58,18 @@ def test_append_wrong_arg_type(self) -> None:
             # noinspection PyTypeChecker
             propfile.append(obj)
 
+    def test_append_list_of_wrong_arg_type(self) -> None:
+        # GIVEN normal instance of PropFile
+        propfile = PropFile(Config())
+
+        # WHEN we try to append list of object of unsupported type
+        obj = ['INVALID']
+
+        # THEN Exception should be thrown.
+        with self.assertRaises(TypeError):
+            # noinspection PyTypeChecker
+            propfile.append(obj)
+
     # #################################################################################################
 
     def test_load_non_existing_file(self) -> None:
@@ -224,18 +237,18 @@ def assertBlank(blank):
             self.assertIsNone(blank.value)
 
         comment1_marker = '#'
-        comment1_value = self.get_random_string('comment_')
+        comment1_value = self.get_random_string('comment')
 
-        key1 = self.get_random_string('key1_')
+        key1 = self.get_random_string('key1')
         sep1 = '='
-        val1 = self.get_random_string('val1_')
+        val1 = self.get_random_string('val1')
 
         comment2_marker = '!'
-        comment2_value = self.get_random_string('comment_')
+        comment2_value = self.get_random_string('comment')
 
-        key2 = self.get_random_string('key2_')
+        key2 = self.get_random_string('key2')
         sep2 = '='
-        val2 = self.get_random_string('val2_')
+        val2 = self.get_random_string('val2')
 
         fake_data_src = [
             '',
@@ -339,9 +352,10 @@ def test_save_no_target_file(self) -> None:
     # #################################################################################################
 
     @patch('pathlib.Path.exists')
-    def test_is_valid_on_empty_files(self, path_exists_mock: Mock) -> None:
-
+    def test_validate_on_empty_files(self, path_exists_mock: Mock) -> None:
         config = Config()
+        ConfigBuilder._setup_checkers(config)  # noqa: WPS437
+
         fake_file = Path(f'/does/not/matter/{self.get_random_string()}')
         with patch('builtins.open', mock_open(read_data = '')):
             # Lie our fake file exists
@@ -357,10 +371,29 @@ def test_is_valid_on_empty_files(self, path_exists_mock: Mock) -> None:
             propfile.report.dump()
             self.assertTrue(propfile.validate(ref_file))
 
+    @patch('pathlib.Path.exists')
+    def test_validate_no_checkers_configured(self, path_exists_mock: Mock) -> None:
+        # GIVEN empty config without checkers set up
+        config = Config()
+
+        # and GIVEN fake file
+        fake_file = Path(f'/does/not/matter/{self.get_random_string()}')
+        with patch('builtins.open', mock_open(read_data = '')):
+            # Lie our fake file exists
+            path_exists_mock.return_value = True
+            propfile = PropFile(config)
+            propfile.load(fake_file)
+
+            # THEN we expect error raised
+            with self.assertRaises(RuntimeError):
+                # attempting to validate the file
+                propfile.validate(propfile)
+
     # #################################################################################################
 
     def test_update(self) -> None:
         config = Config()
+        ConfigBuilder._setup_checkers(config)  # noqa: WPS437
 
         # Generate reference file and its contents
         reference = self._generate_propfile_with_content(config)
@@ -397,7 +430,7 @@ def test_update(self) -> None:
         for _ in range(max_items):
             translation.append([
                 Blank(),
-                Comment(self.get_random_string('comment_')),
+                Comment(self.get_random_string('comment')),
             ])
 
         # THEN after update
@@ -427,3 +460,20 @@ def test_update(self) -> None:
                     continue
 
             self.fail(f'Unknown item type: {type(trans_item)}')
+
+    def test_update_fail_on_unknown_type(self) -> None:
+        """
+        Ensures unexpected and unsupported content will be caught and raise TypeError.
+        """
+        config = Config()
+
+        # GIVEN Translation and Reference objects
+        reference = PropFile(config)
+        trans = PropFile(config)
+
+        # When reference contents contain invalid item
+        reference.items.append(False)
+
+        # THEN attempt to update() should fail with error raised.
+        with self.assertRaises(TypeError):
+            trans.update(reference)
diff --git a/tests/prop/test_translation.py b/tests/prop/test_translation.py
index 563ce62..f93b06d 100644
--- a/tests/prop/test_translation.py
+++ b/tests/prop/test_translation.py
@@ -20,7 +20,7 @@ class SplitTest(TestCase):
     """
 
     def __init__(self, fmt: str, mid_val_sep = True):
-        key = self.get_random_string('key_', length = 10)
+        key = self.get_random_string('key', length = 10)
         sep = random.choice(Config.ALLOWED_SEPARATORS)
         val_sep = random.choice(Config.ALLOWED_SEPARATORS) if mid_val_sep else ''
         val = self.get_random_string(length = 10) + val_sep + self.get_random_string(length = 10)
@@ -142,7 +142,7 @@ def test_parse_translation_line_invalid_entries(self) -> None:
     def test_parse_translation_line_escaped_chars(self) -> None:
         key = r'this\=is\:\key'
         sep = random.choice(Config.ALLOWED_SEPARATORS)
-        val = self.get_random_string('value_')
+        val = self.get_random_string('value')
         line = f'{key}{sep}{val}'
 
         res = Translation.parse_translation_line(line)
diff --git a/tests/report/test_report_group.py b/tests/report/test_report_group.py
index aef8cdc..730bfa7 100644
--- a/tests/report/test_report_group.py
+++ b/tests/report/test_report_group.py
@@ -62,3 +62,23 @@ def test_error(self) -> None:
         self.assertIsInstance(item, Error)
         self.assertEqual(0, self.rg.warnings)
         self.assertEqual(1, self.rg.errors)
+
+    def test_add_with_list(self) -> None:
+        """
+        Ensures add() deals with all the cases properly.
+        :return:
+        """
+
+        reports = [
+            Warn(None, msg = self.get_random_string()),
+            Error(None, msg = self.get_random_string()),
+        ]
+        nones = [
+            None,
+            None,
+        ]
+
+        rg = ReportGroup(self.get_random_string('label'))
+        rg.add(reports + nones)
+        # None's should be silently skipped
+        self.assertEqual(len(reports), rg.errors + rg.warnings)
diff --git a/tests/test_case.py b/tests/test_case.py
index bff05ab..66a49c2 100644
--- a/tests/test_case.py
+++ b/tests/test_case.py
@@ -17,7 +17,10 @@ class TestCase(unittest.TestCase):
     def get_random_string_list(self, count, str_prefix: str = '', str_length: int = 16) -> List[str]:
         return [self.get_random_string(str_prefix, str_length) for _ in range(count)]
 
-    def get_random_string(self, prefix: str = '', length: int = 16) -> str:
+    def get_random_string(self, prefix: str = '', length: int = 16, prefix_end = '_') -> str:
+        if prefix:
+            if prefix[-1] != prefix_end:
+                prefix += prefix_end
         for _ in range(length):
             single_char = chr(random.randint(ord('A'), ord('Z')))
             if random.randint(0, 1):
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 5d6eecd..bdb4072 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -82,7 +82,7 @@ def test_add_if_not_in_dict(self) -> None:
 
         # Try adding new elements
         for _ in range(count):
-            key = self.get_random_string('key_')
+            key = self.get_random_string('key')
             val = self.get_random_string()
             Utils.add_if_not_in_dict(src, key, val)
             Utils.add_if_not_in_dict(target, key, val)
@@ -125,7 +125,7 @@ def test_remove_quotes_from_list(self) -> None:
             self.assertEqual(item, val)
 
     def test_remove_quotes_from_dict(self) -> None:
-        key = self.get_random_string('key_')
+        key = self.get_random_string('key')
         val_1 = self.get_random_string()
         val_2 = self.get_random_string()
         val_3 = self.get_random_string()
diff --git a/transtool/checks/substitutions.py b/transtool/checks/substitutions.py
index bdb0ba5..e8762fb 100644
--- a/transtool/checks/substitutions.py
+++ b/transtool/checks/substitutions.py
@@ -24,7 +24,8 @@ class Substitutions(Check):
     checks if all opened brackets are closed.
     """
 
-    FAIL = -1
+    FLAG_DEFAULT = 0
+    FLAG_FAIL_WITH_ERROR = -1
 
     def __init__(self, config: Union[Dict, None] = None):
         super().__init__(config)
@@ -34,13 +35,15 @@ def _find_most_important_issue(self, idx: int, item: PropItem) -> Union[ReportIt
         warns = []
         for config in self.config['map']:
             for match in re.finditer(config['regexp'], item.value):
-                if config['replace'] == self.FAIL:
-                    return ReportGroup.build_error(f'{idx + 1}:{match.start()}', f'Invalid sequence "{match.group(1)}".', item.key)
-                else:
-                    replacement = config['replace']
-                    warns.append(
-                        ReportGroup.build_warn(f'{idx + 1}:{match.start()}', f'Sequence can be replaced with "{replacement}".',
-                                               item.key))
+                at = f'{idx + 1}:{match.start()}'
+
+                if 'flag' in config and config['flag'] == self.FLAG_FAIL_WITH_ERROR:
+                    msg = f'Invalid sequence "{match.group(1)}".'
+                    return ReportGroup.build_error(at, msg, item.key)
+
+                replacement = config['replace']
+                msg = f'Sequence at {at} can be replaced with "{replacement}".'
+                warns.append(ReportGroup.build_warn(at, msg, item.key))
 
         return warns[0] if (isinstance(warns, list) and warns) else None
 
@@ -50,18 +53,9 @@ def check(self, translation: 'PropFile', reference: 'PropFile' = None) -> Report
         self.need_valid_config()
 
         report = ReportGroup('Substitutions')
-
-        if not translation.items:
-            return report
-
-        for idx, item in enumerate(translation.items):
-            # Do not try to be clever and filter() data first, because line_number values will no longer be correct.
-            if self._shall_skip_item(item):
-                continue
-
-            check_result = self._find_most_important_issue(idx, item)
-            if check_result is not None:
-                report.add(check_result)
+        if translation.items:
+            report.add([self._find_most_important_issue(idx, item) for idx, item in enumerate(translation.items) if
+                        not self._shall_skip_item(item)])
 
         return report
 
@@ -71,23 +65,22 @@ def get_default_config(self) -> Dict:
             'comments': False,
 
             # Keep matching elements at the same positions
-            'map':      [
+            'map': [
                 {
-                    'regexp':  r'([\.]{3})',
+                    'regexp': r'([\.]{3})',
                     'replace': '…',
-                },
-                {
-                    'regexp':  r'([\.]{4,})',
-                    'replace': self.FAIL,
-                },
-
-                {
-                    'regexp':  r'([\s]{2,})',
+                    'flag': self.FLAG_DEFAULT,
+                }, {
+                    'regexp': r'([\.]{4,})',
+                    'flag': self.FLAG_FAIL_WITH_ERROR,
+                }, {
+                    'regexp': r'([\s]{2,})',
                     'replace': ' ',
-                },
-                {
-                    'regexp':  r'([\!]{2,})',
+                    'flag': self.FLAG_DEFAULT,
+                }, {
+                    'regexp': r'([\!]{2,})',
                     'replace': '!',
+                    'flag': self.FLAG_DEFAULT,
                 },
             ],
         }
diff --git a/transtool/config/builder.py b/transtool/config/builder.py
index ab208e9..94c52c3 100644
--- a/transtool/config/builder.py
+++ b/transtool/config/builder.py
@@ -6,7 +6,6 @@
 # https://github.com/MarcinOrlowski/trans-tool/
 #
 """
-
 import argparse
 import re
 from pathlib import Path
@@ -36,31 +35,30 @@
 class ConfigBuilder(object):
     # List of options that can be either turned on or off.
     _on_off_pairs = [
-        'fatal',
         'color',
+        'fatal',
+    ]
+
+    _default_checkers = [
+        Brackets,
+        DanglingKeys,
+        EmptyTranslations,
+        FormattingValues,
+        KeyFormat,
+        MissingTranslations,
+        Punctuation,
+        QuotationMarks,
+        StartsWithTheSameCase,
+        Substitutions,
+        TrailingWhiteChars,
+        TypesettingQuotationMarks,
+        WhiteCharsBeforeLinefeed,
     ]
 
     @staticmethod
     def build(config_defaults: Config):
-        checkers = [
-            Brackets,
-            DanglingKeys,
-            EmptyTranslations,
-            FormattingValues,
-            KeyFormat,
-            MissingTranslations,
-            Punctuation,
-            QuotationMarks,
-            StartsWithTheSameCase,
-            TrailingWhiteChars,
-            TypesettingQuotationMarks,
-            WhiteCharsBeforeLinefeed,
-            Substitutions,
-        ]
-
-        for checker in checkers:
-            checker_id = checker.__name__
-            config_defaults.checks[checker_id] = CheckerInfo(checker_id, checker, (checker()).get_default_config())
+        # Let's populate default config with all the supported checkers first
+        ConfigBuilder._setup_checkers(config_defaults)
 
         # Handler CLI args so we can see if there's config file to load
         args = ConfigBuilder._parse_args()
@@ -72,8 +70,18 @@ def build(config_defaults: Config):
         # override with command line arguments
         ConfigBuilder._set_from_args(config_defaults, args)
 
+        ConfigBuilder._get_checkers_from_args(config_defaults, args.checkers)
+
         ConfigBuilder._validate_config(config_defaults)
 
+    @staticmethod
+    def _setup_checkers(config: Config, checkers_list: Union[List[str], None] = None) -> None:
+        if checkers_list is None:
+            checkers_list = ConfigBuilder._default_checkers
+        for checker in checkers_list:
+            checker_id = checker.__name__
+            config.checks[checker_id] = CheckerInfo(checker_id, checker, (checker()).get_default_config())
+
     @staticmethod
     def _abort(msg: str) -> None:
         Log.e(msg)
@@ -143,12 +151,29 @@ def _set_from_args(config: Config, args) -> None:
             ConfigBuilder._add_file_suffix(config, args.files)
             Utils.add_if_not_in_list(config.files, args.files)
 
+    @staticmethod
+    def _get_checkers_from_args(config: Config, args_checkers: Union[List[str], None]) -> None:
+        """
+        If `--checks` argument list is provided, used checkers will be adjusted according to
+        values (Checker IDs) provided.
+        :param config:
+        :param args_checkers:
+        """
+        all_checkers = {checker.__name__.lower(): checker for checker in ConfigBuilder._default_checkers}
+        if args_checkers:
+            checkers = []
+            for checker_id in args_checkers:
+                if checker_id.lower() not in all_checkers:
+                    ConfigBuilder._abort(f'Unknown checker ID "{checker_id}".')
+                Utils.add_if_not_in_list(checkers, checker_id)
+            ConfigBuilder._setup_checkers(config, checkers)
+
     @staticmethod
     def _add_file_suffix(config: Config, files: Union[List[Path], None]) -> None:
         if files:
             suffix_len = len(config.file_suffix)
             for idx, file in enumerate(files):
-                # 'PosixPath' object is not subscriptable, so we cannot slice it.
+                # 'PosixPath' object cannot be sliced.
                 path_str = str(file)
                 if path_str[suffix_len * -1:] != config.file_suffix:
                     files[idx] = Path(f'{path_str}{config.file_suffix}')
@@ -185,7 +210,7 @@ def _parse_args() -> argparse:
                            help = f'Default file name suffix. Default: "{Config.DEFAULT_FILE_SUFFIX}".')
 
         group = parser.add_argument_group('Checks controlling options')
-        group.add_argument('--checks', action = 'store', dest = 'checks', nargs = '+', metavar = 'CHECK_ID',
+        group.add_argument('--checks', action = 'store', dest = 'checkers', nargs = '+', metavar = 'CHECK_ID',
                            help = 'List of checks ID to be executed. By default all available checks are run.')
 
         group.add_argument('-f', '--fatal', action = 'store_true', dest = 'fatal',
diff --git a/transtool/config/config.py b/transtool/config/config.py
index 5867787..2b03b73 100644
--- a/transtool/config/config.py
+++ b/transtool/config/config.py
@@ -60,6 +60,8 @@ def __init__(self):
         }
 
     def set_checker_config(self, checker_id: str, config: Dict) -> None:
+        if not isinstance(config, dict):
+            raise TypeError(f'Checker config must be a dictionary, {type(config)} given.')
         self.checks[checker_id] = config
 
     def get_checker_config(self, checker_id: str) -> Dict:
@@ -67,7 +69,7 @@ def get_checker_config(self, checker_id: str) -> Dict:
             raise KeyError(f'No config for {checker_id} found.')
         return self.checks[checker_id]
 
-    def _dump(self, items: Dict):
+    def _dump_recursive(self, items: Dict):
         for key, val in items.items():
             if isinstance(val, str):
                 print(f'{key} = "{val}"')  # noqa: WPS421
@@ -79,7 +81,7 @@ def _dump(self, items: Dict):
 
             if isinstance(val, dict):
                 print()  # noqa: WPS421
-                self._dump(val)
+                self._dump_recursive(val)
                 continue
 
             if isinstance(val, list):
@@ -88,7 +90,7 @@ def _dump(self, items: Dict):
 
             if isinstance(val, CheckerInfo):
                 print(f'[{val.id}]')  # noqa: WPS421
-                self._dump(val.config)
+                self._dump_recursive(val.config)
                 print()  # noqa: WPS421
                 continue
 
@@ -100,4 +102,4 @@ def _dump(self, items: Dict):
             return
 
     def dump(self) -> None:
-        self._dump(self.__dict__['checks'])
+        self._dump_recursive(self.__dict__['checks'])
diff --git a/transtool/config/reader.py b/transtool/config/reader.py
index 2b89ad4..b30dcfe 100644
--- a/transtool/config/reader.py
+++ b/transtool/config/reader.py
@@ -69,6 +69,7 @@ def read(self, config: Config, config_file_name: Path) -> Config:
 
         self._merge_if_exists(self.parser, config.files, main_section, 'files')
         self._merge_if_exists(self.parser, config.languages, main_section, 'languages')
+        self._merge_if_exists(self.parser, config.checks, main_section, 'checks')
 
         if config.debug:
             for attr_name in dir(config):
diff --git a/transtool/const.py b/transtool/const.py
index 05b91ad..2146381 100644
--- a/transtool/const.py
+++ b/transtool/const.py
@@ -12,7 +12,7 @@
 
 class Const(object):
     APP_NAME: str = 'trans-tool'
-    APP_VERSION: str = '2.1.0'
+    APP_VERSION: str = '2.2.0'
     APP_URL: str = 'https://github.com/MarcinOrlowski/trans-tool/'
 
     APP_DESCRIPTION: List[str] = [
diff --git a/transtool/main.py b/transtool/main.py
index 15e1532..0a6a0a2 100644
--- a/transtool/main.py
+++ b/transtool/main.py
@@ -19,9 +19,6 @@
 from .utils import Utils
 
 
-# #################################################################################################
-
-
 class TransTool(object):
 
     @staticmethod
diff --git a/transtool/prop/file.py b/transtool/prop/file.py
index 11109cb..d255b34 100644
--- a/transtool/prop/file.py
+++ b/transtool/prop/file.py
@@ -135,7 +135,7 @@ def update(self, reference: 'PropFile') -> None:
                     else:
                         tmp.append(Comment.get_commented_out_key_comment(self.config, item.key, item.value))
             else:
-                raise RuntimeError(f'Unknown entry type: {type(item)} at position {idx + 1}')
+                raise TypeError(f'Unknown entry type: {type(item)} at position {idx + 1}')
 
         self._items = tmp.items
         self.keys = tmp.keys
@@ -150,6 +150,9 @@ def validate(self, reference_file: 'PropFile') -> bool:
         :param reference_file:
         :return: True if file is valid, False if there were errors.
         """
+        if not self.config.checks:
+            raise RuntimeError('Checks config element cannot be empty.')
+
         for _, checker_info in self.config.checks.items():
             checker = checker_info.callable(checker_info.config)
             # Each validator gets copy of the files, to prevent any potential destructive operation.
diff --git a/transtool/report/group.py b/transtool/report/group.py
index d2e0f17..48dcb90 100644
--- a/transtool/report/group.py
+++ b/transtool/report/group.py
@@ -6,8 +6,7 @@
 # https://github.com/MarcinOrlowski/trans-tool/
 #
 """
-
-from typing import Union
+from typing import Union, List
 
 from transtool.log import Log
 from transtool.report.items import Error, ReportItem, Warn
@@ -42,29 +41,47 @@ def create(self, position: Union[str, int, None], msg: str, trans_key: Union[str
     def empty(self) -> bool:
         return (self.errors + self.warnings) == 0
 
-    def add(self, item) -> None:
-        if not issubclass(type(item), ReportItem):
-            raise TypeError(f'Item must be subclass of ReportItem. "{type(item)}" given.')
-        self.append(item)
-        if isinstance(item, Warn):
-            self.warnings += 1
-        else:
-            self.errors += 1
+    def add(self, items: Union[ReportItem, List[ReportItem], None]) -> None:
+        if not items:
+            return
+
+        if not isinstance(items, list):
+            items = [items]
+
+        for item in items:
+            if item is None:
+                continue
+            if not issubclass(type(item), ReportItem):
+                raise TypeError(f'Item must be subclass of ReportItem. "{type(item)}" given.')
+            self.append(item)
+            if isinstance(item, Warn):
+                self.warnings += 1
+            else:
+                self.errors += 1
+
+    @staticmethod
+    def _to_list(line: Union[str, int, None]) -> Union[List[str], None]:
+        """
+        Accepts line variable (of various types) and converts to list of strings.
+        Raises TypeError is provided argument is of not supported type.
+        """
+        if line:
+            if not isinstance(line, (str, int)):
+                raise TypeError(f'Unsupported argument type. "{type(line)}" given.')
+            if not isinstance(line, str):
+                line = str(line)
+        return line
 
     @staticmethod
     def build_warn(line: Union[str, int, None], msg: str, trans_key: Union[str, None] = None) -> Warn:
-        if line and not isinstance(line, str):
-            line = str(line)
-        return Warn(line, msg, trans_key)
+        return Warn(ReportGroup._to_list(line), msg, trans_key)
 
     def warn(self, line: Union[str, int, None], msg: str, trans_key: Union[str, None] = None) -> None:
         self.add(self.build_warn(line, msg, trans_key))
 
     @staticmethod
     def build_error(line: Union[str, int, None], msg: str, trans_key: Union[str, None] = None) -> Error:
-        if isinstance(line, int):
-            line = str(line)
-        return Error(line, msg, trans_key)
+        return Error(ReportGroup._to_list(line), msg, trans_key)
 
     def error(self, line: Union[str, int, None], msg: str, trans_key: Union[str, None] = None) -> None:
         self.add(self.build_error(line, msg, trans_key))