diff --git a/.prospector.yaml b/.prospector.yaml
index 452c66da60..27ee1e3a30 100644
--- a/.prospector.yaml
+++ b/.prospector.yaml
@@ -1,6 +1,14 @@
-strictness: medium
+strictness: veryhigh
 doc-warnings: false
 test-warnings: false
 autodetect: true
 member-warnings: false
 max-line-length: 88
+
+pylint:
+  options:
+    extension-pkg-allow-list:
+      - ujson
+
+mccabe:
+  run: false
diff --git a/.pylintrc b/.pylintrc
index ab8c6a1b0a..686428e7b6 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -3,7 +3,7 @@
 # A comma-separated list of package or module names from where C extensions may
 # be loaded. Extensions are loading into the active Python interpreter and may
 # run arbitrary code
-extension-pkg-whitelist=
+extension-pkg-allow-list=ujson
 
 # Add files or directories to the blacklist. They should be base names, not
 # paths.
diff --git a/onadata/apps/api/tests/viewsets/test_data_viewset.py b/onadata/apps/api/tests/viewsets/test_data_viewset.py
index adc64e9b6a..b6afb10e2c 100644
--- a/onadata/apps/api/tests/viewsets/test_data_viewset.py
+++ b/onadata/apps/api/tests/viewsets/test_data_viewset.py
@@ -233,6 +233,7 @@ def test_data_list_with_xform_in_delete_async_queue(self):
         self.assertEqual(len(response.data), initial_count - 1)
 
     def test_numeric_types_are_rendered_as_required(self):
+        """Test numeric types are rendered as numeric."""
         tutorial_folder = os.path.join(
             os.path.dirname(__file__), "..", "fixtures", "forms", "tutorial"
         )
@@ -244,6 +245,7 @@ def test_numeric_types_are_rendered_as_required(self):
         create_instance(self.user.username, open(instance_path, "rb"), [])
 
         self.assertEqual(self.xform.instances.count(), 1)
+
         view = DataViewSet.as_view({"get": "list"})
         request = self.factory.get("/", **self.extra)
         response = view(request, pk=self.xform.id)
@@ -253,6 +255,16 @@ def test_numeric_types_are_rendered_as_required(self):
         self.assertEqual(response.data[0].get("net_worth"), 100000.00)
         self.assertEqual(response.data[0].get("imei"), "351746052009472")
 
+        # test when fields parameter is used.
+        fields_query = {"fields": '["_id", "age", "net_worth", "imei"]'}
+        request = self.factory.get("/", data=fields_query, **self.extra)
+        response = view(request, pk=self.xform.id)
+        self.assertEqual(response.status_code, 200, response.data)
+        # check that ONLY values with numeric and decimal types are converted
+        self.assertEqual(response.data[0].get("age"), 35)
+        self.assertEqual(response.data[0].get("net_worth"), 100000.00)
+        self.assertEqual(response.data[0].get("imei"), "351746052009472")
+
     def test_data_jsonp(self):
         self._make_submissions()
         view = DataViewSet.as_view({"get": "list"})
diff --git a/onadata/apps/logger/tests/models/test_instance.py b/onadata/apps/logger/tests/models/test_instance.py
index 06741cc3a5..3716a1894d 100644
--- a/onadata/apps/logger/tests/models/test_instance.py
+++ b/onadata/apps/logger/tests/models/test_instance.py
@@ -195,7 +195,7 @@ def test_query_filter_by_integer(self):
             )
         ]
         self.assertEqual(len(data), 1)
-        self.assertEqual(data, [str(oldest)])
+        self.assertEqual(data, [oldest])
 
         # mongo $gt
         data = [
diff --git a/onadata/apps/main/tests/test_form_api.py b/onadata/apps/main/tests/test_form_api.py
index 3308fc6e87..a10abf1be9 100644
--- a/onadata/apps/main/tests/test_form_api.py
+++ b/onadata/apps/main/tests/test_form_api.py
@@ -1,3 +1,7 @@
+# -*- coding: utf-8 -*-
+"""
+Test onadata.apps.main.views.api.
+"""
 import base64
 import json
 
@@ -6,30 +10,24 @@
 
 from onadata.apps.main.tests.test_base import TestBase
 from onadata.apps.main.views import api
-from onadata.apps.viewer.models.parsed_instance import ParsedInstance
 from onadata.libs.utils.mongo import _decode_from_mongo, _encode_for_mongo
 
 
-def dict_for_mongo_without_userform_id(parsed_instance):
-    d = parsed_instance.to_dict_for_mongo()
-    # remove _userform_id since its not returned by the API
-    d.pop(ParsedInstance.USERFORM_ID)
-    return d
-
-
 class TestFormAPI(TestBase):
+    """Test the form API endpoint."""
 
     def setUp(self):
-        super(TestBase, self).setUp()
+        super().setUp()
         self.factory = RequestFactory()
         self._create_user_and_login()
         self._publish_transportation_form_and_submit_instance()
-        self.api_url = reverse(api, kwargs={
-            'username': self.user.username,
-            'id_string': self.xform.id_string
-        })
+        self.api_url = reverse(
+            api,
+            kwargs={"username": self.user.username, "id_string": self.xform.id_string},
+        )
 
     def test_api(self):
+        """Test the forms /api endpoint."""
         request = self.factory.get(self.api_url, {})
         request.user = self.user
         response = api(request, self.user.username, self.xform.id_string)
@@ -43,119 +41,145 @@ def test_api(self):
         self.assertEqual(find_d, data)
 
     def test_api_with_query(self):
+        """Test the query param for forms API endpoint."""
         # query string
-        query = '{"transport/available_transportation_types_to_referral_facil'\
-                'ity":"none"}'
-        data = {'query': query}
+        query = (
+            '{"transport/available_transportation_types_to_referral_facil'
+            'ity":"none"}'
+        )
+        data = {"query": query}
         response = self.client.get(self.api_url, data)
         self.assertEqual(response.status_code, 200)
-        d = self.xform.instances.all()[0].json
+        data = self.xform.instances.all()[0].json
         find_d = json.loads(response.content)[0]
-        self.assertEqual(find_d, d)
+        self.assertEqual(find_d, data)
 
     def test_api_query_no_records(self):
+        """Test query param that returns no records."""
         # query string
         query = {
-            "transport/available_transporation_types_to_referral_facility":
-            "bicycle"
+            "transport/available_transporation_types_to_referral_facility": "bicycle"
         }
-        data = {'query': json.dumps(query)}
+        data = {"query": json.dumps(query)}
         response = self.client.get(self.api_url, data)
-        self.assertEqual(response.status_code, 200)
-        self.assertEqual(response.content, b'[]')
-        data['fields'] = '["_id"]'
+        self.assertEqual(response.status_code, 200, response.content)
+        self.assertEqual(response.content, b"[]")
+        data["fields"] = '["_id"]'
         response = self.client.get(self.api_url, data)
-        self.assertEqual(response.status_code, 200)
-        self.assertEqual(response.content, b'[]')
+        self.assertEqual(response.status_code, 200, response.content)
+        self.assertEqual(response.content, b"[]")
 
     def test_handle_bad_json(self):
-        response = self.client.get(self.api_url, {'query': '{bad'})
-        self.assertEqual(response.status_code, 400)
+        """Test a bad query is handled correctly with status 400."""
+        response = self.client.get(self.api_url, {"query": "{bad"})
+        self.assertContains(
+            response,
+            "Expecting property name enclosed in double quotes",
+            status_code=400,
+        )
 
     def test_api_jsonp(self):
+        """Test support for jsonp response at the API endpoint."""
         # query string
-        callback = 'jsonpCallback'
-        response = self.client.get(self.api_url, {'callback': callback})
+        callback = "jsonpCallback"
+        response = self.client.get(self.api_url, {"callback": callback})
         self.assertEqual(response.status_code, 200)
-        content = response.content.decode('utf-8')
-        self.assertEqual(content.startswith(callback + '('), True)
-        self.assertEqual(content.endswith(')'), True)
-        start = callback.__len__() + 1
-        end = content.__len__() - 1
-        content = content[start: end]
-        d = self.xform.instances.all()[0].json
+        content = response.content.decode("utf-8")
+        self.assertEqual(content.startswith(callback + "("), True)
+        self.assertEqual(content.endswith(")"), True)
+        start = len(callback) + 1
+        end = len(content) - 1
+        content = content[start:end]
+        data = self.xform.instances.all()[0].json
         find_d = json.loads(content)[0]
-        self.assertEqual(find_d, d)
+        self.assertEqual(find_d, data)
 
     def test_api_with_query_start_limit(self):
+        """Test start and limit query parameters."""
         for i in range(1, 3):
             self._submit_transport_instance(i)
         # query string
-        data = {'start': 0, 'limit': 2}
+        data = {"start": 0, "limit": 2}
         response = self.client.get(self.api_url, data)
         self.assertEqual(response.status_code, 200)
         content = json.loads(response.content)
         self.assertEqual(len(content), 2)
-        data['fields'] = '["_id"]'
+        data["fields"] = '["_id"]'
         response = self.client.get(self.api_url, data)
         self.assertEqual(response.status_code, 200)
         content = json.loads(response.content)
         self.assertEqual(len(content), 2)
 
+    # pylint: disable=invalid-name
     def test_api_with_query_invalid_start_limit(self):
+        """Test start and limit query parameters with invalid values."""
         # query string
-        query = '{"transport/available_transportation_types_to_referral_facil'\
-                'ity":"none"}'
-        data = {'query': query, 'start': -100, 'limit': -100}
+        query = (
+            '{"transport/available_transportation_types_to_referral_facil'
+            'ity":"none"}'
+        )
+        data = {"query": query, "start": -100, "limit": -100}
         response = self.client.get(self.api_url, data)
-        self.assertEqual(response.status_code, 400)
+        self.assertContains(response, "Invalid start/limit params", status_code=400)
 
-        data = {'query': query, 'start': 'invalid', 'limit': 'invalid'}
+        data = {"query": query, "start": "invalid", "limit": "invalid"}
         response = self.client.get(self.api_url, data)
-        self.assertEqual(response.status_code, 400)
+        self.assertContains(
+            response, "invalid literal for int() with base 10:", status_code=400
+        )
 
     def test_api_count(self):
+        """Test count parameter at the form API endpoint."""
         # query string
-        query = '{"transport/available_transportation_types_to_referral_facil'\
-                'ity":"none"}'
-        data = {'query': query, 'count': 1}
+        query = (
+            '{"transport/available_transportation_types_to_referral_facil'
+            'ity":"none"}'
+        )
+        data = {"query": query, "count": 1}
         response = self.client.get(self.api_url, data)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 200, response.content)
         find_d = json.loads(response.content)[0]
-        self.assertTrue('count' in find_d)
+        self.assertTrue("count" in find_d)
 
-        data['fields'] = '["_id"]'
+        data["fields"] = '["_id"]'
         response = self.client.get(self.api_url, data)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 200, response.content)
         find_d = json.loads(response.content)[0]
-        self.assertTrue('count' in find_d)
-        self.assertEqual(find_d.get('count'), 1)
+        self.assertTrue("count" in find_d)
+        self.assertEqual(find_d.get("count"), 1)
 
     def test_api_column_select(self):
+        """Test fields parameter at the API endpoint."""
         # query string
-        query = '{"transport/available_transportation_types_to_referral_facil'\
-                'ity":"none"}'
-        columns = '["transport/available_transportation_types_to_referral_fac'\
-                  'ility"]'
-        data = {'query': query, 'fields': columns}
+        query = (
+            '{"transport/available_transportation_types_to_referral_facility":"none"}'
+        )
+        columns = '["transport/available_transportation_types_to_referral_facility"]'
+        data = {"query": query, "fields": columns}
         request = self.factory.get(self.api_url, data)
         request.user = self.user
         response = api(request, self.user.username, self.xform.id_string)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 200, response.content)
         find_d = json.loads(response.content)[0]
         self.assertTrue(
-            'transport/available_transportation_types_to_referral_facility' in
-            find_d)
-        self.assertFalse('_attachments' in find_d)
+            "transport/available_transportation_types_to_referral_facility" in find_d
+        )
+        self.assertFalse("_attachments" in find_d)
 
     def test_api_decode_from_mongo(self):
+        """Test API decodes Mongo DB symbols."""
         field = "$section1.group01.question1"
         encoded = _encode_for_mongo(field)
-        self.assertEqual(encoded, (
-            "%(dollar)ssection1%(dot)sgroup01%(dot)squestion1" % {
-                "dollar": base64.b64encode(
-                    '$'.encode('utf-8')).decode('utf-8'),
-                "dot": base64.b64encode('.'.encode('utf-8')).decode('utf-8')}))
+        self.assertEqual(
+            encoded,
+            (
+                "%(dollar)ssection1%(dot)sgroup01%(dot)squestion1"
+                % {
+                    "dollar": base64.b64encode("$".encode("utf-8")).decode("utf-8"),
+                    "dot": base64.b64encode(".".encode("utf-8")).decode("utf-8"),
+                }
+            ),
+        )
         decoded = _decode_from_mongo(encoded)
         self.assertEqual(field, decoded)
 
@@ -171,20 +195,20 @@ def test_api_with_or_query(self):
         # record 2: 'transport/loop_over_transport_types_frequency/ambulance/fr
         #           equency_to_referral_facility': 'weekly'
         params = {
-            'query':
-            '{"$or": [{"transport/loop_over_transport_types_frequency/ambulanc'
+            "query": '{"$or": [{"transport/loop_over_transport_types_frequency/ambulanc'
             'e/frequency_to_referral_facility": "weekly"}, {"transport/loop_ov'
-            'er_transport_types_frequency/ambulance/frequency_to_referral_faci'
-            'lity": "daily"}]}'}
+            "er_transport_types_frequency/ambulance/frequency_to_referral_faci"
+            'lity": "daily"}]}'
+        }
         response = self.client.get(self.api_url, params)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 200, response.content)
         data = json.loads(response.content)
         self.assertEqual(len(data), 2)
 
         # check with fields filter
-        params['fields'] = '["_id"]'
+        params["fields"] = '["_id"]'
         response = self.client.get(self.api_url, params)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 200, response.content)
         data = json.loads(response.content)
         self.assertEqual(len(data), 2)
 
@@ -196,11 +220,12 @@ def test_api_with_or_query(self):
         self.assertEqual(len(data), 3)
 
     def test_api_cors_options(self):
+        """Test CORS options at the API endpoint."""
         response = self.anon.options(self.api_url)
-        allowed_headers = ['Accept', 'Origin', 'X-Requested-With',
-                           'Authorization']
-        provided_headers = [h.strip() for h in response[
-            'Access-Control-Allow-Headers'].split(',')]
+        allowed_headers = ["Accept", "Origin", "X-Requested-With", "Authorization"]
+        provided_headers = [
+            h.strip() for h in response["Access-Control-Allow-Headers"].split(",")
+        ]
         self.assertListEqual(allowed_headers, provided_headers)
-        self.assertEqual(response['Access-Control-Allow-Methods'], 'GET')
-        self.assertEqual(response['Access-Control-Allow-Origin'], '*')
+        self.assertEqual(response["Access-Control-Allow-Methods"], "GET")
+        self.assertEqual(response["Access-Control-Allow-Origin"], "*")
diff --git a/onadata/apps/viewer/models/parsed_instance.py b/onadata/apps/viewer/models/parsed_instance.py
index 7984695898..e91e058d62 100644
--- a/onadata/apps/viewer/models/parsed_instance.py
+++ b/onadata/apps/viewer/models/parsed_instance.py
@@ -3,7 +3,6 @@
 ParsedInstance model
 """
 import datetime
-import json
 import types
 
 from django.conf import settings
@@ -12,6 +11,7 @@
 from django.utils.translation import gettext as _
 
 import six
+import ujson as json
 from dateutil import parser
 
 from onadata.apps.logger.models.instance import Instance, _get_attachments_from_instance
@@ -136,7 +136,9 @@ def parse_json(data):
             yield parse_json(row[0]) if row[0] else None
     else:
         for row in cursor.fetchall():
-            yield dict(zip(fields, row))
+            yield dict(
+                zip(fields, (json.loads(s) if isinstance(s, str) else s for s in row))
+            )
 
 
 def get_etag_hash_from_query(queryset, sql=None, params=None):
@@ -144,9 +146,10 @@ def get_etag_hash_from_query(queryset, sql=None, params=None):
     if not isinstance(queryset, EmptyQuerySet):
         if sql is None:
             sql, params = queryset.query.sql_with_params()
+        from_index = sql.find("FROM ")
         sql = (
             "SELECT md5(string_agg(date_modified::text, ''))"
-            " FROM (SELECT date_modified " + sql[sql.find("FROM ") :] + ") AS A"
+            " FROM (SELECT date_modified " + sql[from_index:] + ") AS A"
         )
         etag_hash = [i for i in _query_iterator(sql, params=params) if i is not None]
 
@@ -181,7 +184,8 @@ def _start_index_limit(records, sql, fields, params, sort, start_index, limit):
         and not fields
         and not has_json_fields
     ):
-        records = records[start_index : start_index + limit]
+        end_index = start_index + limit
+        records = records[start_index:end_index]
     if start_index is not None and limit is None and not fields and not has_json_fields:
         records = records[start_index:]
 
@@ -349,7 +353,6 @@ class ParsedInstance(models.Model):
     )
     start_time = models.DateTimeField(null=True)
     end_time = models.DateTimeField(null=True)
-    # TODO: decide if decimal field is better than float field.
     lat = models.FloatField(null=True)
     lng = models.FloatField(null=True)
 
@@ -444,8 +447,6 @@ def _get_name_for_type(self, type_value):
                 return item["name"]
         return None
 
-    # TODO: figure out how much of this code should be here versus
-    # data_dictionary.py.
     def _set_geopoint(self):
         if self.instance.point:
             self.lat = self.instance.point.y
@@ -474,6 +475,7 @@ def remove_note(self, note_id):
         note.delete()
 
     def get_notes(self):
+        """Returns a list of notes data objects."""
         notes = []
         note_qs = self.instance.notes.values(
             "id", "note", "date_created", "date_modified"
diff --git a/requirements/base.pip b/requirements/base.pip
index 7e8fbd0c32..ce82639247 100644
--- a/requirements/base.pip
+++ b/requirements/base.pip
@@ -377,6 +377,8 @@ tabulator==1.53.5
     # via
     #   datapackage
     #   tableschema
+ujson==5.3.0
+    # via onadata
 unicodecsv==0.14.1
     # via
     #   datapackage
diff --git a/requirements/dev.pip b/requirements/dev.pip
index f1d4a95328..9adbc3ff6d 100644
--- a/requirements/dev.pip
+++ b/requirements/dev.pip
@@ -513,6 +513,8 @@ traitlets==5.2.2.post1
     # via
     #   ipython
     #   matplotlib-inline
+ujson==5.3.0
+    # via onadata
 unicodecsv==0.14.1
     # via
     #   datapackage
diff --git a/setup.cfg b/setup.cfg
index c1c33c1fd0..0c53480db1 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -108,6 +108,7 @@ install_requires =
     # Google exports
     google-auth-oauthlib
     google-auth
+    ujson
 python_requires = >= 3.9
 setup_requires =
     setuptools_scm