diff --git a/gcp_variant_transforms/libs/bigquery_schema_descriptor.py b/gcp_variant_transforms/libs/bigquery_schema_descriptor.py
new file mode 100644
index 000000000..f7002d106
--- /dev/null
+++ b/gcp_variant_transforms/libs/bigquery_schema_descriptor.py
@@ -0,0 +1,75 @@
+# Copyright 2018 Google Inc.  All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""A dict based description for BigQuery schema."""
+
+from __future__ import absolute_import
+
+from typing import NamedTuple
+from apache_beam.io.gcp.internal.clients import bigquery  # pylint: disable=unused-import
+
+
+# Stores data about a simple field (not a record) in BigQuery Schema.
+FieldDescriptor = NamedTuple('FieldDescriptor', [('type', str), ('mode', str)])
+
+
+class SchemaDescriptor(object):
+  """A dict based description for :class:`bigquery.TableSchema` object.
+
+     This class provides APIs for checking if and how (e.g. type, mode) a field
+     is defined in the BigQuery schema. This is useful when checking if
+     data matches its field definition in the schema for example.
+  """
+
+  def __init__(self, table_schema):
+    # type: (bigquery.TableSchema) -> None
+
+    # Dict of (field_name, :class:`FieldDescriptor`).
+    self._field_descriptor_dict = {}
+    # Dict of (record_name, :class:`SchemaDescriptor`).
+    self._schema_descriptor_dict = {}
+
+    self._extract_all_descriptors(table_schema)
+
+  def _extract_all_descriptors(self, table_schema):
+    # type: (bigquery.TableSchema) -> None
+    """Extracts descriptor for fields and records in `table_schema`."""
+    for field in table_schema.fields:
+      if field.fields:
+        # Record field.
+        self._schema_descriptor_dict[field.name] = SchemaDescriptor(field)
+      else:
+        # Simple field.
+        self._field_descriptor_dict[field.name] = FieldDescriptor(
+            type=field.type, mode=field.mode)
+
+  def get_field_descriptor(self, field_name):
+    # type: (str) -> FieldDescriptor
+    """Returns :class:`FieldDescriptor obj for the given field.
+
+    Args:
+      field_name: name of a simple (not a record) field in BigQuery table.
+    """
+    if field_name in self._field_descriptor_dict:
+      return self._field_descriptor_dict[field_name]
+    else:
+      raise ValueError('Field descriptor not found. Not such field in Bigquery '
+                       'schema: {}'.format(field_name))
+
+  def get_record_schema_descriptor(self, record_name):
+    # type: (str) -> SchemaDescriptor
+    if record_name in self._schema_descriptor_dict:
+      return self._schema_descriptor_dict[record_name]
+    else:
+      raise ValueError('Schema descriptor not found. No such record '
+                       'in Bigquery schema: {}'.format(record_name))
diff --git a/gcp_variant_transforms/libs/bigquery_schema_descriptor_test.py b/gcp_variant_transforms/libs/bigquery_schema_descriptor_test.py
new file mode 100644
index 000000000..a4eac622a
--- /dev/null
+++ b/gcp_variant_transforms/libs/bigquery_schema_descriptor_test.py
@@ -0,0 +1,111 @@
+# Copyright 2018 Google Inc.  All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for bigquery_schema_descriptor module."""
+
+
+from __future__ import absolute_import
+
+import unittest
+
+from apache_beam.io.gcp.internal.clients import bigquery
+from gcp_variant_transforms.libs.bigquery_util import TableFieldConstants as Consts
+from gcp_variant_transforms.libs import bigquery_schema_descriptor
+
+
+class SchemaDescriptorTest(unittest.TestCase):
+  """Test case for :class:`SchemaDescriptor`."""
+
+  def _get_table_schema(self):
+    # type (None) -> bigquery.TableSchema
+    schema = bigquery.TableSchema()
+    schema.fields.append(bigquery.TableFieldSchema(
+        name='field_1', type=Consts.TYPE_STRING, mode=Consts.MODE_NULLABLE))
+    schema.fields.append(bigquery.TableFieldSchema(
+        name='field_2', type=Consts.TYPE_INTEGER, mode=Consts.MODE_REPEATED))
+    # Record field.
+    record_field = bigquery.TableFieldSchema(
+        name='record_1', type=Consts.TYPE_RECORD, mode=Consts.MODE_REPEATED,
+        )
+    record_field.fields.append(bigquery.TableFieldSchema(
+        name='record_1_field_1', type=Consts.TYPE_BOOLEAN,
+        mode=Consts.MODE_NULLABLE, ))
+    record_field.fields.append(bigquery.TableFieldSchema(
+        name='record_1_field_2', type=Consts.TYPE_FLOAT,
+        mode=Consts.MODE_REPEATED))
+    # Record field, two level deep.
+    deep_record_field = bigquery.TableFieldSchema(
+        name='record_1-record_2', type=Consts.TYPE_RECORD,
+        mode=Consts.MODE_REPEATED)
+    deep_record_field.fields.append(bigquery.TableFieldSchema(
+        name='record_1-record_2_field_1', type=Consts.TYPE_BOOLEAN,
+        mode=Consts.MODE_NULLABLE))
+
+    record_field.fields.append(deep_record_field)
+    schema.fields.append(record_field)
+    return schema
+
+  def _get_schema_descriptor(self):
+    return bigquery_schema_descriptor.SchemaDescriptor(
+        self._get_table_schema())
+
+  def test_non_existence_field(self):
+    schema = self._get_schema_descriptor()
+    with self.assertRaises(ValueError):
+      schema.get_field_descriptor('non_existence_field')
+      self.fail('Non existence field should throw an exceprion')
+
+  def test_non_existence_record(self):
+    schema = self._get_schema_descriptor()
+    with self.assertRaises(ValueError):
+      schema.get_record_schema_descriptor('non_existence_record')
+      self.fail('Non existence field should throw an exceprion')
+
+  def test_field_descriptor_at_first_level(self):
+    schema = self._get_schema_descriptor()
+
+    self.assertEqual(
+        schema.get_field_descriptor('field_1'),
+        bigquery_schema_descriptor.FieldDescriptor(
+            type=Consts.TYPE_STRING, mode=Consts.MODE_NULLABLE))
+    self.assertEqual(
+        schema.get_field_descriptor('field_2'),
+        bigquery_schema_descriptor.FieldDescriptor(
+            type=Consts.TYPE_INTEGER, mode=Consts.MODE_REPEATED))
+
+  def test_field_descriptor_at_second_level(self):
+    main_schema = self._get_schema_descriptor()
+    record_schema = main_schema.get_record_schema_descriptor('record_1')
+
+    self.assertEqual(
+        record_schema.get_field_descriptor('record_1_field_1'),
+        bigquery_schema_descriptor.FieldDescriptor(
+            type=Consts.TYPE_BOOLEAN, mode=Consts.MODE_NULLABLE))
+    self.assertEqual(
+        record_schema.get_field_descriptor('record_1_field_2'),
+        bigquery_schema_descriptor.FieldDescriptor(
+            type=Consts.TYPE_FLOAT, mode=Consts.MODE_REPEATED))
+
+  def test_field_descriptor_at_third_level(self):
+    main_schema = self._get_schema_descriptor()
+    parent_record_schema = main_schema.get_record_schema_descriptor(
+        'record_1')
+    child_record_schema = parent_record_schema.get_record_schema_descriptor(
+        'record_1-record_2')
+
+    self.assertEqual(
+        child_record_schema.get_field_descriptor(
+            'record_1-record_2_field_1'),
+        bigquery_schema_descriptor.FieldDescriptor(
+            type=Consts.TYPE_BOOLEAN, mode=Consts.MODE_NULLABLE))