diff --git a/.vscode/settings.json b/.vscode/settings.json
index 9355f26b..8a37642b 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -13,6 +13,6 @@
 			"mode": "auto"
 		}
 	],
-	"python.linting.pylintEnabled": true,
-	"python.linting.enabled": true
+	"python.linting.enabled": true,
+	"python.linting.mypyEnabled": true
 }
\ No newline at end of file
diff --git a/README.md b/README.md
index f4c08ffc..5d24f39f 100644
--- a/README.md
+++ b/README.md
@@ -76,6 +76,10 @@ This readme file is used mostly to document project dependencies
 <summary>requirements_dev</summary>
   <pre>
   - coverage
+  - pylint
+  - mypy
+  - django-stubs[compatible-mypy]
+  - djangorestframework-stubs[compatible-mypy]
   </pre>
 </details>
 <details>
diff --git a/rsconcept/RunLint.ps1 b/rsconcept/RunLint.ps1
index eb253d39..c47debec 100644
--- a/rsconcept/RunLint.ps1
+++ b/rsconcept/RunLint.ps1
@@ -2,5 +2,7 @@
 Set-Location $PSScriptRoot\backend
 
 $pylint = "$PSScriptRoot\backend\venv\Scripts\pylint.exe"
+$mypy = "$PSScriptRoot\backend\venv\Scripts\mypy.exe"
 
-& $pylint cctext project apps
\ No newline at end of file
+& $pylint cctext project apps
+& $mypy cctext project apps
\ No newline at end of file
diff --git a/rsconcept/backend/apps/rsform/models.py b/rsconcept/backend/apps/rsform/models.py
index e0712e0d..40a5aded 100644
--- a/rsconcept/backend/apps/rsform/models.py
+++ b/rsconcept/backend/apps/rsform/models.py
@@ -1,14 +1,18 @@
 ''' Models: RSForms for conceptual schemas. '''
 import json
 import pyconcept
-from django.db import models, transaction
+from django.db import transaction
+from django.db.models import (
+    CASCADE, SET_NULL, ForeignKey, Model, PositiveIntegerField, QuerySet,
+    TextChoices, TextField, BooleanField, CharField, DateTimeField, JSONField
+)
 from django.core.validators import MinValueValidator
 from django.core.exceptions import ValidationError
 from django.urls import reverse
 from apps.users.models import User
 
 
-class CstType(models.TextChoices):
+class CstType(TextChoices):
     ''' Type of constituenta '''
     BASE = 'basic'
     CONSTANT = 'constant'
@@ -20,7 +24,7 @@ class CstType(models.TextChoices):
     THEOREM = 'theorem'
 
 
-class Syntax(models.TextChoices):
+class Syntax(TextChoices):
     ''' Syntax types '''
     UNDEF = 'undefined'
     ASCII = 'ascii'
@@ -31,35 +35,35 @@ def _empty_forms():
     return []
 
 
-class RSForm(models.Model):
+class RSForm(Model):
     ''' RSForm is a math form of capturing conceptual schema '''
-    owner = models.ForeignKey(
+    owner: ForeignKey = ForeignKey(
         verbose_name='Владелец',
         to=User,
-        on_delete=models.SET_NULL,
+        on_delete=SET_NULL,
         null=True
     )
-    title = models.TextField(
+    title: TextField = TextField(
         verbose_name='Название'
     )
-    alias = models.CharField(
+    alias: CharField = CharField(
         verbose_name='Шифр',
         max_length=255,
         blank=True
     )
-    comment = models.TextField(
+    comment: TextField = TextField(
         verbose_name='Комментарий',
         blank=True
     )
-    is_common = models.BooleanField(
+    is_common: BooleanField = BooleanField(
         verbose_name='Общая',
         default=False
     )
-    time_create = models.DateTimeField(
+    time_create: DateTimeField = DateTimeField(
         verbose_name='Дата создания',
         auto_now_add=True
     )
-    time_update = models.DateTimeField(
+    time_update: DateTimeField = DateTimeField(
         verbose_name='Дата изменения',
         auto_now=True
     )
@@ -69,7 +73,7 @@ class RSForm(models.Model):
         verbose_name = 'Схема'
         verbose_name_plural = 'Схемы'
 
-    def constituents(self) -> models.QuerySet:
+    def constituents(self) -> QuerySet:
         ''' Get QuerySet containing all constituents of current RSForm '''
         return Constituenta.objects.filter(schema=self)
 
@@ -162,7 +166,7 @@ class RSForm(models.Model):
             else:
                 cst = Constituenta.create_from_trs(cst_data, self, order)
                 cst.save()
-                uid = cst.id
+                uid = cst.pk
             loaded_ids.add(uid)
             order += 1
         for prev_cst in prev_constituents:
@@ -186,10 +190,10 @@ class RSForm(models.Model):
         schema._create_items_from_trs(data['items'])
         return schema
 
-    def to_trs(self) -> str:
+    def to_trs(self) -> dict:
         ''' Generate JSON string containing all data from RSForm '''
         result = self._prepare_json_rsform()
-        items: list['Constituenta'] = self.constituents().order_by('order')
+        items = self.constituents().order_by('order')
         for cst in items:
             result['items'].append(cst.to_trs())
         return result
@@ -200,7 +204,7 @@ class RSForm(models.Model):
     def get_absolute_url(self):
         return reverse('rsform-detail', kwargs={'pk': self.pk})
 
-    def _prepare_json_rsform(self: 'Constituenta') -> dict:
+    def _prepare_json_rsform(self: 'RSForm') -> dict:
         return {
             'type': 'rsform',
             'title': self.title,
@@ -211,10 +215,10 @@ class RSForm(models.Model):
 
     @transaction.atomic
     def _update_from_core(self) -> dict:
-        checked = json.loads(pyconcept.check_schema(json.dumps(self.to_trs())))
+        checked: dict = json.loads(pyconcept.check_schema(json.dumps(self.to_trs())))
         update_list = self.constituents().only('id', 'order')
         if len(checked['items']) != update_list.count():
-            raise ValidationError
+            raise ValidationError('Invalid constituents count')
         order = 1
         for cst in checked['items']:
             cst_id = cst['entityUID']
@@ -235,59 +239,59 @@ class RSForm(models.Model):
             order += 1
 
 
-class Constituenta(models.Model):
+class Constituenta(Model):
     ''' Constituenta is the base unit for every conceptual schema '''
-    schema = models.ForeignKey(
+    schema: ForeignKey = ForeignKey(
         verbose_name='Концептуальная схема',
         to=RSForm,
-        on_delete=models.CASCADE
+        on_delete=CASCADE
     )
-    order = models.PositiveIntegerField(
+    order: PositiveIntegerField = PositiveIntegerField(
         verbose_name='Позиция',
         validators=[MinValueValidator(1)],
         default=-1,
     )
-    alias = models.CharField(
+    alias: CharField = CharField(
         verbose_name='Имя',
         max_length=8,
         default='undefined'
     )
-    cst_type = models.CharField(
+    cst_type: CharField = CharField(
         verbose_name='Тип',
         max_length=10,
         choices=CstType.choices,
         default=CstType.BASE
     )
-    convention = models.TextField(
+    convention: TextField = TextField(
         verbose_name='Комментарий/Конвенция',
         default='',
         blank=True
     )
-    term_raw = models.TextField(
+    term_raw: TextField = TextField(
         verbose_name='Термин (с отсылками)',
         default='',
         blank=True
     )
-    term_resolved = models.TextField(
+    term_resolved: TextField = TextField(
         verbose_name='Термин',
         default='',
         blank=True
     )
-    term_forms = models.JSONField(
+    term_forms: JSONField = JSONField(
         verbose_name='Словоформы',
         default=_empty_forms
     )
-    definition_formal = models.TextField(
+    definition_formal: TextField = TextField(
         verbose_name='Родоструктурное определение',
         default='',
         blank=True
     )
-    definition_raw = models.TextField(
+    definition_raw: TextField = TextField(
         verbose_name='Текстовое определние (с отсылками)',
         default='',
         blank=True
     )
-    definition_resolved = models.TextField(
+    definition_resolved: TextField = TextField(
         verbose_name='Текстовое определние',
         default='',
         blank=True
@@ -342,9 +346,9 @@ class Constituenta(models.Model):
             self.term_resolved = ''
             self.term_forms = []
 
-    def to_trs(self) -> str:
+    def to_trs(self) -> dict:
         return {
-            'entityUID': self.id,
+            'entityUID': self.pk,
             'type': 'constituenta',
             'cstType': self.cst_type,
             'alias': self.alias,
diff --git a/rsconcept/backend/apps/rsform/serializers.py b/rsconcept/backend/apps/rsform/serializers.py
index a45e7746..11b16fac 100644
--- a/rsconcept/backend/apps/rsform/serializers.py
+++ b/rsconcept/backend/apps/rsform/serializers.py
@@ -73,7 +73,7 @@ class RSFormDetailsSerlializer(serializers.BaseSerializer):
         trs = pyconcept.check_schema(json.dumps(instance.to_trs()))
         trs = trs.replace('entityUID', 'id')
         result = json.loads(trs)
-        result['id'] = instance.id
+        result['id'] = instance.pk
         result['time_update'] = instance.time_update
         result['time_create'] = instance.time_create
         result['is_common'] = instance.is_common
@@ -101,7 +101,7 @@ class ConstituentaSerializer(serializers.ModelSerializer):
         if 'definition_raw' in validated_data:
             validated_data['definition_resolved'] = validated_data['definition_raw']
 
-        result = super().update(instance, validated_data)
+        result: Constituenta = super().update(instance, validated_data)
         instance.schema.save()
         return result
 
diff --git a/rsconcept/backend/apps/rsform/tests/t_views.py b/rsconcept/backend/apps/rsform/tests/t_views.py
index 6041f0b1..301074d3 100644
--- a/rsconcept/backend/apps/rsform/tests/t_views.py
+++ b/rsconcept/backend/apps/rsform/tests/t_views.py
@@ -16,7 +16,7 @@ from apps.rsform.views import (
 
 
 def _response_contains(response, schema: RSForm) -> bool:
-    return any(x for x in response.data if x['id'] == schema.id)
+    return any(x for x in response.data if x['id'] == schema.pk)
 
 
 class TestConstituentaAPI(APITestCase):
@@ -25,8 +25,8 @@ class TestConstituentaAPI(APITestCase):
         self.user = User.objects.create(username='UserTest')
         self.client = APIClient()
         self.client.force_authenticate(user=self.user)
-        self.rsform_owned: RSForm = RSForm.objects.create(title='Test', alias='T1', owner=self.user)
-        self.rsform_unowned: RSForm = RSForm.objects.create(title='Test2', alias='T2')
+        self.rsform_owned = RSForm.objects.create(title='Test', alias='T1', owner=self.user)
+        self.rsform_unowned = RSForm.objects.create(title='Test2', alias='T2')
         self.cst1 = Constituenta.objects.create(
             alias='X1', schema=self.rsform_owned, order=1, convention='Test')
         self.cst2 = Constituenta.objects.create(
@@ -87,8 +87,8 @@ class TestRSFormViewset(APITestCase):
         self.user = User.objects.create(username='UserTest')
         self.client = APIClient()
         self.client.force_authenticate(user=self.user)
-        self.rsform_owned: RSForm = RSForm.objects.create(title='Test', alias='T1', owner=self.user)
-        self.rsform_unowned: RSForm = RSForm.objects.create(title='Test2', alias='T2')
+        self.rsform_owned = RSForm.objects.create(title='Test', alias='T1', owner=self.user)
+        self.rsform_unowned = RSForm.objects.create(title='Test2', alias='T2')
 
     def test_create_anonymous(self):
         self.client.logout()
@@ -131,7 +131,7 @@ class TestRSFormViewset(APITestCase):
 
     def test_contents(self):
         schema = RSForm.objects.create(title='Title1')
-        schema.insert_last(alias='X1', type=CstType.BASE)
+        schema.insert_last(alias='X1', insert_type=CstType.BASE)
         response = self.client.get(f'/api/rsforms/{schema.id}/contents/')
         self.assertEqual(response.status_code, 200)
 
@@ -418,9 +418,9 @@ class TestLibraryAPI(APITestCase):
         self.user = User.objects.create(username='UserTest')
         self.client = APIClient()
         self.client.force_authenticate(user=self.user)
-        self.rsform_owned: RSForm = RSForm.objects.create(title='Test', alias='T1', owner=self.user)
-        self.rsform_unowned: RSForm = RSForm.objects.create(title='Test2', alias='T2')
-        self.rsform_common: RSForm = RSForm.objects.create(title='Test3', alias='T3', is_common=True)
+        self.rsform_owned = RSForm.objects.create(title='Test', alias='T1', owner=self.user)
+        self.rsform_unowned = RSForm.objects.create(title='Test2', alias='T2')
+        self.rsform_common = RSForm.objects.create(title='Test3', alias='T3', is_common=True)
 
     def test_retrieve_common(self):
         self.client.logout()
diff --git a/rsconcept/backend/apps/rsform/utils.py b/rsconcept/backend/apps/rsform/utils.py
index b987923f..8e372cdc 100644
--- a/rsconcept/backend/apps/rsform/utils.py
+++ b/rsconcept/backend/apps/rsform/utils.py
@@ -21,7 +21,8 @@ def read_trs(file) -> dict:
     ''' Read JSON from TRS file '''
     with ZipFile(file, 'r') as archive:
         json_data = archive.read('document.json')
-    return json.loads(json_data)
+    result: dict = json.loads(json_data)
+    return result
 
 
 def write_trs(json_data: dict) -> bytes:
diff --git a/rsconcept/backend/apps/rsform/views.py b/rsconcept/backend/apps/rsform/views.py
index 97255456..b7b9a4b6 100644
--- a/rsconcept/backend/apps/rsform/views.py
+++ b/rsconcept/backend/apps/rsform/views.py
@@ -53,7 +53,7 @@ class RSFormViewSet(viewsets.ModelViewSet):
     ordering = '-time_update'
 
     def _get_schema(self) -> models.RSForm:
-        return self.get_object()
+        return self.get_object() # type: ignore
 
     def perform_create(self, serializer):
         if not self.request.user.is_anonymous and 'owner' not in self.request.POST:
@@ -114,7 +114,7 @@ class RSFormViewSet(viewsets.ModelViewSet):
     @action(detail=True, methods=['patch'], url_path='cst-moveto')
     def cst_moveto(self, request, pk):
         ''' Endpoint: Move multiple constituents. '''
-        schema: models.RSForm = self._get_schema()
+        schema = self._get_schema()
         serializer = serializers.CstMoveSerlializer(data=request.data, context={'schema': schema})
         serializer.is_valid(raise_exception=True)
         schema.move_cst(serializer.validated_data['constituents'], serializer.validated_data['move_to'])
diff --git a/rsconcept/backend/cctext/__init__.py b/rsconcept/backend/cctext/__init__.py
index dc23dee3..7c60c16a 100644
--- a/rsconcept/backend/cctext/__init__.py
+++ b/rsconcept/backend/cctext/__init__.py
@@ -1,4 +1,5 @@
 ''' Concept core text processing library. '''
+# pylint: skip-file
 from .syntax import RuSyntax, Capitalization
 from .rumodel import Morphology, SemanticRole, WordTag, morpho
 from .ruparser import PhraseParser, WordToken, Collation
diff --git a/rsconcept/backend/cctext/rumodel.py b/rsconcept/backend/cctext/rumodel.py
index cd8cae38..aad798db 100644
--- a/rsconcept/backend/cctext/rumodel.py
+++ b/rsconcept/backend/cctext/rumodel.py
@@ -1,6 +1,7 @@
 ''' Russian language models. '''
 from __future__ import annotations
 from enum import Enum, unique
+from typing import Iterable
 
 from pymorphy2 import MorphAnalyzer
 from pymorphy2.tagset import OpencorporaTag as WordTag
@@ -59,14 +60,14 @@ class Morphology:
         return pos in ['ADJF', 'ADJS', 'PRTF', 'PRTS']
 
     @property
-    def effective_pos(self) -> str:
+    def effective_POS(self) -> str:
         ''' Access part of speech. Pronouns are considered as nouns '''
-        pos = self.tag.POS
+        pos: str = self.tag.POS
         if pos and self.tag.POS == 'NPRO':
             return 'NOUN'
         return pos
 
-    def complete_tags(self, tags: frozenset[str]) -> set[str]:
+    def complete_tags(self, tags: Iterable[str]) -> set[str]:
         ''' Add missing tags before inflection. '''
         result = set(tags)
         pos = self.tag.POS
@@ -111,6 +112,7 @@ class Morphology:
         if count == 0:
             return ''
         elif count == 1:
-            return next(iter(grammemes))
+            result: str = next(iter(grammemes))
+            return result
         else:
             return ','.join(grammemes)
diff --git a/rsconcept/backend/cctext/ruparser.py b/rsconcept/backend/cctext/ruparser.py
index f9603989..7a8acd00 100644
--- a/rsconcept/backend/cctext/ruparser.py
+++ b/rsconcept/backend/cctext/ruparser.py
@@ -1,5 +1,6 @@
 ''' Parsing russian language using pymorphy2 and natasha libraries. '''
 from __future__ import annotations
+from typing import Iterable, Optional
 
 from razdel.substring import Substring as Segment
 from pymorphy2.analyzer import Parse as WordForm
@@ -11,17 +12,16 @@ INDEX_NONE = -1
 NO_COORDINATION = -1
 WORD_NONE = -1
 
+Tags = Iterable[str]
+
 
 class WordToken:
-    ''' Minimal text token. '''
+    ''' Atomic text token. '''
     def __init__(self, segment: Segment, forms: list[WordForm], main_form: int = 0):
         self.segment: Segment = segment
         self.forms: list[WordForm] = forms
         self.main: int = main_form
 
-    def __del__(self):
-        pass
-
     def get_morpho(self) -> Morphology:
         ''' Return morphology for current token. '''
         return Morphology(self.get_form().tag)
@@ -30,7 +30,7 @@ class WordToken:
         ''' Access main form. '''
         return self.forms[self.main]
 
-    def inflect(self, inflection_tags: set[str]):
+    def inflect(self, inflection_tags: set[str]) -> Optional[WordForm]:
         ''' Apply inflection to segment text. Does not modify forms '''
         inflected = self.get_form().inflect(inflection_tags)
         if not inflected:
@@ -43,21 +43,20 @@ class Collation:
     ''' Parsed data for input coordinated text. '''
     def __init__(self, text: str):
         self.text = text
-        self.words = []
-        self.coordination = []
+        self.words: list[WordToken] = []
+        self.coordination: list[int] = []
         self.main_word: int = WORD_NONE
 
-    def __del__(self):
-        pass
+    def is_valid(self) -> bool:
+        ''' Check if data is parsed correctly '''
+        return self.main_word != WORD_NONE
 
     def get_form(self) -> WordForm:
-        ''' Access main form. '''
+        ''' Access WordForm. '''
         return self.words[self.main_word].get_form()
 
     def get_morpho(self) -> Morphology:
         ''' Access parsed main mrophology. '''
-        if self.main_word == WORD_NONE:
-            return None
         return self.words[self.main_word].get_morpho()
 
     def add_word(self, segment, forms: list, main_form: int, need_coordination: bool = True):
@@ -65,28 +64,29 @@ class Collation:
         self.words.append(WordToken(segment, forms, main_form))
         self.coordination.append(NO_COORDINATION if not need_coordination else 0)
 
-    def inflect(self, target_tags: frozenset[str]) -> str:
+    def inflect(self, target_tags: Tags) -> str:
         ''' Inflect text to match required tags. '''
-        origin = self.get_morpho()
-        if not origin or origin.tag.grammemes.issuperset(target_tags):
-            return self.text
-        if not self._apply_inflection(origin, target_tags):
-            return self.text
-        new_text = self._generate_text()
-        return new_text
+        if self.is_valid():
+            origin = self.get_morpho()
+            if not origin.tag.grammemes.issuperset(target_tags):
+                if self._apply_inflection(origin, target_tags):
+                    return self._generate_text()
+        return self.text
 
     def inflect_like(self, base_model: Collation) -> str:
         ''' Create inflection to substitute base_model form. '''
-        morph = base_model.get_morpho()
-        if morph.effective_pos is None:
-            return self.text
-        tags = set()
-        tags.add(morph.effective_pos)
-        tags = morph.complete_tags(tags)
-        return self.inflect(tags)
+        if self.is_valid():
+            morph = base_model.get_morpho()
+            if morph.effective_POS:
+                tags = set()
+                tags.add(morph.effective_POS)
+                tags = morph.complete_tags(tags)
+                return self.inflect(tags)
+        return self.text
 
     def inflect_dependant(self, master_model: Collation) -> str:
         ''' Create inflection to coordinate with master_model form. '''
+        assert self.is_valid()
         morph = master_model.get_morpho()
         tags = morph.coordination_tags()
         tags = self.get_morpho().complete_tags(tags)
@@ -94,12 +94,12 @@ class Collation:
 
     def normal_form(self) -> str:
         ''' Generate normal form. '''
-        main_form = self.get_form()
-        if not main_form:
-            return self.text
-        new_morpho = Morphology(main_form.normalized.tag)
-        new_tags = new_morpho.complete_tags(frozenset())
-        return self.inflect(new_tags)
+        if self.is_valid():
+            main_form = self.get_form()
+            new_morpho = Morphology(main_form.normalized.tag)
+            new_tags = new_morpho.complete_tags(frozenset())
+            return self.inflect(new_tags)
+        return self.text
 
     def _iterate_coordinated(self):
         words_count = len(self.words)
@@ -108,21 +108,20 @@ class Collation:
             yield self.words[current_word]
             current_word += self.coordination[current_word]
 
-    def _inflect_main_word(self, origin: Morphology, target_tags: frozenset[str]) -> Morphology:
+    def _inflect_main_word(self, origin: Morphology, target_tags: Tags) -> Optional[Morphology]:
         full_tags = origin.complete_tags(target_tags)
         inflected = self.words[self.main_word].inflect(full_tags)
         if not inflected:
             return None
         return Morphology(inflected.tag)
 
-    def _apply_inflection(self, origin: Morphology, target_tags: frozenset[str]) -> bool:
+    def _apply_inflection(self, origin: Morphology, target_tags: Tags) -> bool:
         new_moprho = self._inflect_main_word(origin, target_tags)
         if not new_moprho:
             return False
         inflection_tags = new_moprho.coordination_tags()
         if len(inflection_tags) == 0:
             return True
-
         for word in self._iterate_coordinated():
             word.inflect(inflection_tags)
         return True
@@ -155,13 +154,17 @@ class PhraseParser:
     _MAIN_WAIT_LIMIT = 10  # count words untill fixing main
     _MAIN_MAX_FOLLOWERS = 3  # count words after main as coordination candidates
 
-    def parse(self, text: str, require_index: int = INDEX_NONE, require_tags: frozenset[str] = None) -> Collation:
-        ''' Determine morpho tags for input text.
-        ::returns:: Morphology of a text or None if no suitable form is available '''
-        if text == '':
-            return None
+    def parse(self, text: str,
+              require_index: int = INDEX_NONE,
+              require_tags: Optional[Tags] = None) -> Optional[Collation]:
+        ''' 
+        Determine morpho tags for input text.
+        ::returns:: Morphology of a text or None if no suitable form is available 
+        '''
         segments = list(RuSyntax.tokenize(text))
-        if len(segments) == 1:
+        if len(segments) == 0:
+            return None
+        elif len(segments) == 1:
             return self._parse_single(segments[0], require_index, require_tags)
         else:
             return self._parse_multiword(text, segments, require_index, require_tags)
@@ -169,9 +172,9 @@ class PhraseParser:
     def normalize(self, text: str):
         ''' Get normal form for target text. '''
         processed = self.parse(text)
-        if not processed:
-            return text
-        return processed.normal_form()
+        if processed:
+            return processed.normal_form()
+        return text
 
     def find_substr(self, text: str, sub: str) -> tuple[int, int]:
         ''' Search for substring position in text regardless of morphology. '''
@@ -234,7 +237,7 @@ class PhraseParser:
             return dependant_normal
         return dependant_model.inflect_dependant(master_model)
 
-    def _parse_single(self, segment, require_index: int, require_tags: frozenset[str]) -> Collation:
+    def _parse_single(self, segment, require_index: int, require_tags: Optional[Tags]) -> Optional[Collation]:
         forms = list(self._filtered_parse(segment.text))
         parse_index = INDEX_NONE
         if len(forms) == 0 or require_index >= len(forms):
@@ -266,9 +269,10 @@ class PhraseParser:
         result.main_word = 0
         return result
 
-    def _parse_multiword(self, text: str, segments: list, require_index: int, require_tags: frozenset[str]):
+    def _parse_multiword(self, text: str, segments: list, require_index: int,
+                         require_tags: Optional[Tags]) -> Optional[Collation]:
         result = Collation(text)
-        priority_main = self._PRIORITY_NONE
+        priority_main: float = self._PRIORITY_NONE
         segment_index = 0
         main_wait = 0
         word_index = 0
@@ -295,20 +299,20 @@ class PhraseParser:
                        output: Collation,
                        segment: Segment,
                        require_index: int,
-                       require_tags: frozenset[str]) -> float:
+                       require_tags: Optional[Tags]) -> Optional[float]:
         ''' Return priority for this can be a new main word '''
         forms = list(self._filtered_parse(segment.text))
         if len(forms) == 0:
             return None
-        main_index = INDEX_NONE
-        segment_score = self._PRIORITY_NONE
+        main_index: int = INDEX_NONE
+        segment_score: float = self._PRIORITY_NONE
         needs_coordination = False
-        local_sum = 0
-        score_sum = 0
+        local_sum: float = 0
+        score_sum: float = 0
         if require_index != INDEX_NONE:
             form = forms[require_index]
             if not require_tags or form.tag.grammemes.issuperset(require_tags):
-                (local_max, segment_score) = PhraseParser._get_priority_for(form.tag)
+                (local_max, segment_score) = PhraseParser._get_priorities_for(form.tag)
                 main_index = require_index
                 needs_coordination = Morphology.is_dependable(form.tag.POS)
         else:
@@ -316,7 +320,7 @@ class PhraseParser:
             for (index, form) in enumerate(forms):
                 if require_tags and not form.tag.grammemes.issuperset(require_tags):
                     continue
-                (local_priority, global_priority) = PhraseParser._get_priority_for(form.tag)
+                (local_priority, global_priority) = PhraseParser._get_priorities_for(form.tag)
                 needs_coordination = needs_coordination or Morphology.is_dependable(form.tag.POS)
                 local_sum += global_priority * form.score
                 score_sum += form.score
@@ -414,7 +418,8 @@ class PhraseParser:
                 yield form
 
     @staticmethod
-    def _parse_word(text: str, require_index: int = INDEX_NONE, require_tags: frozenset[str] = None) -> Morphology:
+    def _parse_word(text: str, require_index: int = INDEX_NONE,
+                    require_tags: Optional[Tags] = None) -> Optional[Morphology]:
         parsed_variants = morpho.parse(text)
         if not parsed_variants or require_index >= len(parsed_variants):
             return None
@@ -432,7 +437,7 @@ class PhraseParser:
         return None
 
     @staticmethod
-    def _get_priority_for(tag: WordTag) -> tuple[float, float]:
+    def _get_priorities_for(tag: WordTag) -> tuple[float, float]:
         ''' Return pair of local and global priorities. '''
         if tag.POS in ['VERB', 'INFN']:
             return (9, 10)
@@ -447,7 +452,9 @@ class PhraseParser:
         return (0, 0)
 
     @staticmethod
-    def _choose_context_etalon(target: Morphology, before: Collation, after: Collation) -> Collation:
+    def _choose_context_etalon(target: Morphology,
+                               before: Optional[Collation],
+                               after: Optional[Collation]) -> Optional[Collation]:
         if not before or not before.get_morpho().can_coordinate:
             return after
         if not after or not after.get_morpho().can_coordinate:
@@ -473,7 +480,7 @@ class PhraseParser:
         return before
 
     @staticmethod
-    def _combine_morpho(target: Morphology, etalon: WordTag) -> str:
+    def _combine_morpho(target: Morphology, etalon: WordTag) -> frozenset[str]:
         part_of_speech = target.tag.POS
         number = etalon.number
         if number == 'plur':
diff --git a/rsconcept/backend/cctext/syntax.py b/rsconcept/backend/cctext/syntax.py
index ff3c5eb9..b3bb593d 100644
--- a/rsconcept/backend/cctext/syntax.py
+++ b/rsconcept/backend/cctext/syntax.py
@@ -68,7 +68,11 @@ class RuSyntax:
         ''' Test if text is a single word. '''
         try:
             gen = tokenize(text)
-            return next(gen) == '' or next(gen) == ''
+            if next(gen) == '':
+                return True
+            if next(gen) == '':
+                return True
+            return False
         except StopIteration:
             return True
 
diff --git a/rsconcept/backend/cctext/tests/testRuParser.py b/rsconcept/backend/cctext/tests/testRuParser.py
index 2df9a7d0..0a98013b 100644
--- a/rsconcept/backend/cctext/tests/testRuParser.py
+++ b/rsconcept/backend/cctext/tests/testRuParser.py
@@ -1,6 +1,7 @@
 ''' Test russian language parsing. '''
 import unittest
 
+from typing import Iterable, Optional
 from cctext import PhraseParser
 
 parser = PhraseParser()
@@ -9,16 +10,20 @@ parser = PhraseParser()
 class TestRuParser(unittest.TestCase):
     ''' Test class for russian parsing. '''
 
-    def _assert_parse(self, text: str, expected: list[str], require_index: int = -1, require_tags: list[str] = None):
+    def _assert_parse(self, text: str, expected: list[str],
+                      require_index: int = -1,
+                      require_tags: Optional[Iterable[str]] = None):
         phrase = parser.parse(text, require_index, require_tags)
-        self.assertEqual(phrase.get_morpho().tag.grammemes, set(expected))
+        self.assertIsNotNone(phrase)
+        if phrase:
+            self.assertEqual(phrase.get_morpho().tag.grammemes, set(expected))
 
     def _assert_inflect(self, text: str, tags: list[str], expected: str):
         model = parser.parse(text)
         if not model:
             result = text
         else:
-            result = model.inflect(set(tags))
+            result = model.inflect(frozenset(tags))
         self.assertEqual(result, expected)
 
     def test_parse_word(self):
diff --git a/rsconcept/backend/mypy.ini b/rsconcept/backend/mypy.ini
new file mode 100644
index 00000000..98caa4a0
--- /dev/null
+++ b/rsconcept/backend/mypy.ini
@@ -0,0 +1,23 @@
+# Global options:
+
+[mypy]
+warn_return_any = True
+warn_unused_configs = True
+
+plugins = mypy_drf_plugin.main, mypy_django_plugin.main
+
+# Per-module options:
+[mypy.plugins.django-stubs]
+django_settings_module = "project.settings"
+
+[mypy-django_filters.*]
+ignore_missing_imports = True
+
+[mypy-pyconcept.*]
+ignore_missing_imports = True
+
+[mypy-razdel.*]
+ignore_missing_imports = True
+
+[mypy-pymorphy2.*]
+ignore_missing_imports = True
\ No newline at end of file
diff --git a/rsconcept/backend/project/settings.py b/rsconcept/backend/project/settings.py
index d9c7b91e..d1991044 100644
--- a/rsconcept/backend/project/settings.py
+++ b/rsconcept/backend/project/settings.py
@@ -123,7 +123,7 @@ DATABASES = {
 # Password validation
 # https://docs.djangoproject.com/en/4.1/ref/settings/#auth-password-validators
 
-AUTH_PASSWORD_VALIDATORS = [
+AUTH_PASSWORD_VALIDATORS: list[str] = [
     # NOTE: Password validators disabled
     # {
     #     'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
diff --git a/rsconcept/backend/requirements_dev.txt b/rsconcept/backend/requirements_dev.txt
index 3d2c5107..7a1cfcb7 100644
--- a/rsconcept/backend/requirements_dev.txt
+++ b/rsconcept/backend/requirements_dev.txt
@@ -9,5 +9,8 @@ pymorphy2-dicts-ru
 pymorphy2-dicts-uk
 razdel
 
+mypy
 pylint
-coverage
\ No newline at end of file
+coverage
+django-stubs[compatible-mypy]
+djangorestframework-stubs[compatible-mypy]
\ No newline at end of file