diff --git a/.github/delete-merged-branch-config.yml b/.github/delete-merged-branch-config.yml
new file mode 100644
index 0000000..dca2d98
--- /dev/null
+++ b/.github/delete-merged-branch-config.yml
@@ -0,0 +1,3 @@
+exclude:
+  - develop
+  - master
diff --git a/.travis.yml b/.travis.yml
index 59c8ffb..fe45748 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,7 +17,7 @@ script:
   - pypi-version check
   - cat requirements.txt requirements-tests.txt requirements-dev.txt | safety check --stdin
   - radon cc cli -nb --total-average
-  - isort -rc cli --diff && isort -rc tests --diff
+  - ./scripts/isort-diff.sh
   - flake8 cli && flake8 tests
   - coverage run -m pytest -vv tests
 
diff --git a/README.md b/README.md
index 6640345..c277fcd 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,7 @@
     * [Requirements](#getting-started-requirements)
     * [Installation](#installation)
   * [Usage](#usage)
+    * [Nodes](#nodes)
     * [Configuration file](#configuration-file)
     * [Service](#service)
     * [Account](#account)
@@ -39,6 +40,13 @@ $ pip3 install remme-core-cli
 
 ## Usage
 
+### Nodes
+
+You can use the following list of the addresses of the nodes to execute commands to:
+
+- `node-genesis-testnet.remme.io`,
+- `node-6-testnet.remme.io`.
+
 ### Configuration file
 
 Using the command line interface, you will have an option to declare the `node URL` to send commands to as illustrated below:
@@ -92,10 +100,10 @@ Options:
 
 Get balance of the account by its address — ``remme account get-balance``:
 
-| Arguments | Type   |  Required | Description                                         |
-| :-------: | :----: | :-------: | --------------------------------------------------- |
-| address   | String |  Yes      | Get balance of the account by its address.          |
-| node-url  | String |  No       | Apply the command to the specified node by its URL. |
+| Arguments | Type   |  Required | Description                          |
+| :-------: | :----: | :-------: | ------------------------------------ |
+| address   | String |  Yes      | Account address to get a balance by. |
+| node-url  | String |  No       | Node URL to apply a command to.      |
 
 ```bash
 $ remme account get-balance \
@@ -187,7 +195,11 @@ $ git clone https://github.com/Remmeauth/remme-core-cli && cd remme-core-cli
 $ pip3 install -r requirements.txt -r requirements-dev.txt -r requirements-tests.txt
 ```
 
-When you make changes, ensure your code pass [the checkers](https://github.com/Remmeauth/remme-core-cli/blob/develop/.travis.yml#L16) and is covered by tests using [pytest](https://docs.pytest.org/en/latest).
+When you make changes, ensure your code:
+
+* pass [the checkers](https://github.com/Remmeauth/remme-core-cli/blob/develop/.travis.yml#L16),
+* is covered by tests using [pytest](https://docs.pytest.org/en/latest),
+* follow team [code style](https://github.com/dmytrostriletskyi/nimble-python-code-style-guide).
 
 If you are new for the contribution, please read:
 
@@ -198,10 +210,6 @@ If you are new for the contribution, please read:
 ### Request pull request's review
 
 If you want to your pull request to be review, ensure you:
-- `have wrote the description of the pull request`,
-- `have added at least 2 reviewers`,
-- `continuous integration has been passed`.
-
-![Example of the description and reviewers](https://habrastorage.org/webt/t1/py/cu/t1pycu1bxjslyojlpy50mxb5yie.png)
-
-![Example of the CI which passed](https://habrastorage.org/webt/oz/fl/-n/ozfl-nl-jynrh7ofz8yuz9_gapy.png)
+1. [Branch isn't out-of-date with the base branch](https://habrastorage.org/webt/ux/gi/wm/uxgiwmnft08fubvjfd6d-8pw2wq.png).
+2. [Have written the description of the pull request and have added at least 2 reviewers](https://camo.githubusercontent.com/55c309334a8b61a4848a6ef25f9b0fb3751ae5e9/68747470733a2f2f686162726173746f726167652e6f72672f776562742f74312f70792f63752f7431707963753162786a736c796f6a6c707935306d7862357969652e706e67).
+3. [Continuous integration has been passed](https://habrastorage.org/webt/oz/fl/-n/ozfl-nl-jynrh7ofz8yuz9_gapy.png).
diff --git a/cli/account/cli.py b/cli/account/cli.py
index 106a784..75ebefe 100644
--- a/cli/account/cli.py
+++ b/cli/account/cli.py
@@ -1,20 +1,24 @@
 """
 Provide implementation of the command line interface's account commands.
 """
+import asyncio
 import sys
-import re
 
-import asyncio
 import click
 from remme import Remme
 
+from cli.account.forms import GetAccountBalanceForm
 from cli.account.help import GET_ACCOUNT_BALANCE_ADDRESS_ARGUMENT_HELP_MESSAGE
 from cli.account.service import Account
 from cli.constants import (
-    ADDRESS_REGEXP,
-    FAILED_EXIT_FROM_COMMAND,
+    FAILED_EXIT_FROM_COMMAND_CODE,
     NODE_URL_ARGUMENT_HELP_MESSAGE,
 )
+from cli.utils import (
+    default_node_url,
+    print_errors,
+    print_result,
+)
 
 loop = asyncio.get_event_loop()
 
@@ -28,24 +32,29 @@ def account_commands():
 
 
 @click.option('--address', type=str, required=True, help=GET_ACCOUNT_BALANCE_ADDRESS_ARGUMENT_HELP_MESSAGE)
-@click.option('--node-url', type=str, help=NODE_URL_ARGUMENT_HELP_MESSAGE)
+@click.option('--node-url', type=str, required=False, help=NODE_URL_ARGUMENT_HELP_MESSAGE, default=default_node_url())
 @account_commands.command('get-balance')
 def get_balance(address, node_url):
     """
     Get balance of the account by its address.
     """
-    if re.match(pattern=ADDRESS_REGEXP, string=address) is None:
-        click.echo('The following address `{address}` is not valid.'.format(address=address))
-        sys.exit(FAILED_EXIT_FROM_COMMAND)
+    arguments, errors = GetAccountBalanceForm().load({
+        'address': address,
+        'node_url': node_url,
+    })
+
+    if errors:
+        print_errors(errors)
+        sys.exit(FAILED_EXIT_FROM_COMMAND_CODE)
 
-    if node_url is None:
-        node_url = 'localhost'
+    address = arguments.get('address')
+    node_url = arguments.get('node_url')
 
-    remme = Remme(private_key_hex=None, network_config={
+    remme = Remme(network_config={
         'node_address': str(node_url) + ':8080',
     })
 
-    account = Account(service=remme)
-    balance = loop.run_until_complete(account.get_balance(address=address))
+    account_service = Account(service=remme)
+    balance = loop.run_until_complete(account_service.get_balance(address=address))
 
-    click.echo(balance)
+    print_result(balance)
diff --git a/cli/account/forms.py b/cli/account/forms.py
new file mode 100644
index 0000000..1184e16
--- /dev/null
+++ b/cli/account/forms.py
@@ -0,0 +1,49 @@
+"""
+Provide forms for command line interface's account commands.
+"""
+import re
+
+from marshmallow import (
+    Schema,
+    ValidationError,
+    fields,
+    validates,
+)
+
+from cli.constants import (
+    ADDRESS_REGEXP,
+    DOMAIN_NAME_REGEXP,
+)
+
+
+class GetAccountBalanceForm(Schema):
+    """
+    Get balance of the account form.
+    """
+
+    address = fields.String(required=True)
+    node_url = fields.String(allow_none=True, required=False)
+
+    @validates('address')
+    def validate_address(self, address):
+        """
+        Validate account address.
+        """
+        if re.match(pattern=ADDRESS_REGEXP, string=address) is None:
+            raise ValidationError(f'The following address `{address}` is invalid.')
+
+    @validates('node_url')
+    def validate_node_url(self, node_url):
+        """
+        Validate node URL.
+
+        If node URL is localhost, it means client didn't passed any URL, so nothing to validate.
+        """
+        if node_url == 'localhost':
+            return
+
+        if 'http' in node_url or 'https' in node_url:
+            raise ValidationError(f'Pass the following node URL `{node_url}` without protocol (http, https, etc.).')
+
+        if re.match(pattern=DOMAIN_NAME_REGEXP, string=node_url) is None:
+            raise ValidationError(f'The following node URL `{node_url}` is invalid.')
diff --git a/cli/account/help.py b/cli/account/help.py
index dedd14f..f77a131 100644
--- a/cli/account/help.py
+++ b/cli/account/help.py
@@ -1,4 +1,4 @@
 """
 Provide help messages for command line interface's account commands.
 """
-GET_ACCOUNT_BALANCE_ADDRESS_ARGUMENT_HELP_MESSAGE = 'Get balance of the account by its address.'
+GET_ACCOUNT_BALANCE_ADDRESS_ARGUMENT_HELP_MESSAGE = 'Account address to get a balance by.'
diff --git a/cli/constants.py b/cli/constants.py
index 87013ee..69b1240 100644
--- a/cli/constants.py
+++ b/cli/constants.py
@@ -1,10 +1,14 @@
 """
 Provide constants for command line interface.
 """
-ADDRESS_REGEXP = '[0-9a-f]{70}'
+ADDRESS_REGEXP = r'^[0-9a-f]{70}$'
+DOMAIN_NAME_REGEXP = r'(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]'
 
-FAILED_EXIT_FROM_COMMAND = -1
+PASSED_EXIT_FROM_COMMAND_CODE = 0
+FAILED_EXIT_FROM_COMMAND_CODE = -1
 
 NODE_URL_ARGUMENT_HELP_MESSAGE = 'Apply the command to the specified node by its URL.'
 
 CLI_CONFIG_FILE_NAME = 'remme-core-cli'
+
+NODE_IP_ADDRESS_FOR_TESTING = '159.89.104.9'
diff --git a/cli/utils.py b/cli/utils.py
index 684b002..9f3a4d4 100644
--- a/cli/utils.py
+++ b/cli/utils.py
@@ -3,9 +3,71 @@
 """
 import json
 
+import click
+
 
 def dict_to_pretty_json(data):
-    """
-    Convert dictionary to string with indents as human readable text.
+    r"""
+    Convert dictionary to json with indents (human readable string).
+
+    From the following code:
+        {
+            "address": [
+                "The following address `1120076ecf036e857f42129b5830` is invalid."
+            ]
+        }
+
+    It creates:
+        "{\n    \"address\": [\n        \"The following address `1120076ecf036e857f42129b5830` is invalid.\"    ]\n}\n"
+
+    Notes:
+        - `r` symbol at the start of the documentation is presented because of PEP257.
+
+    References:
+        - https://www.python.org/dev/peps/pep-0257/#id15
+        - https://stackoverflow.com/a/33734332/9632462
     """
     return json.dumps(data, indent=4, sort_keys=True)
+
+
+def print_result(result):
+    """
+    Print successful result to the terminal.
+    """
+    return click.echo(dict_to_pretty_json(result))
+
+
+def print_errors(errors):
+    """
+    Print error messages to the terminal.
+
+    Arguments:
+        errors (dict): dictionary with error messages.
+
+    References:
+        - https://click.palletsprojects.com/en/7.x/utils/#ansi-colors
+    """
+    click.secho(dict_to_pretty_json(errors), blink=True, bold=True, fg='red')
+
+
+def default_node_url():
+    """
+    Get default node URL.
+    """
+    return 'localhost'
+
+
+async def return_async_value(value):
+    """
+    Asynchronous function return value impostor.
+
+    Using for mock particular asynchronous function with specified return value.
+
+    Example of usage in code:
+        mock_account_get_balance = mock.patch('cli.account.service.Account.get_balance')
+        mock_account_get_balance.return_value = return_async_value(13500)
+
+    References:
+        - https://github.com/pytest-dev/pytest-mock/issues/60
+    """
+    return value
diff --git a/requirements.txt b/requirements.txt
index 44223d4..7e36fe6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,3 +2,4 @@ accessify==0.3.1
 asyncio==3.4.3
 click==7.0
 remme==1.0.0
+marshmallow==2.19.2
diff --git a/scripts/isort-diff.sh b/scripts/isort-diff.sh
new file mode 100755
index 0000000..6544762
--- /dev/null
+++ b/scripts/isort-diff.sh
@@ -0,0 +1,13 @@
+#!/bin/bash
+# Check if isort show difference.
+
+ISORT_OUTPUT=$(isort -rc . --diff)
+IS_ISORT_DIFF=$(echo ${ISORT_OUTPUT} | grep '+')
+
+if [ -z "$IS_ISORT_DIFF" ]
+then
+    exit 0
+else
+    echo "${ISORT_OUTPUT}"
+    exit 1
+fi
diff --git a/setup.py b/setup.py
index 6535405..3cdae08 100644
--- a/setup.py
+++ b/setup.py
@@ -1,7 +1,10 @@
 """
 Setup the package.
 """
-from setuptools import find_packages, setup
+from setuptools import (
+    find_packages,
+    setup,
+)
 
 with open('README.md', 'r') as read_me:
     long_description = read_me.read()
diff --git a/tests/test_account.py b/tests/test_account.py
new file mode 100644
index 0000000..37b0051
--- /dev/null
+++ b/tests/test_account.py
@@ -0,0 +1,167 @@
+"""
+Provide tests for command line interface's account commands.
+"""
+import json
+
+from click.testing import CliRunner
+
+from cli.constants import (
+    FAILED_EXIT_FROM_COMMAND_CODE,
+    NODE_IP_ADDRESS_FOR_TESTING,
+    PASSED_EXIT_FROM_COMMAND_CODE,
+)
+from cli.entrypoint import cli
+from cli.utils import (
+    dict_to_pretty_json,
+    return_async_value,
+)
+
+
+def test_get_balance():
+    """
+    Case: get a balance of an account by address.
+    Expect: balance is returned.
+    """
+    runner = CliRunner()
+    result = runner.invoke(cli, [
+        'account',
+        'get-balance',
+        '--address',
+        '1120076ecf036e857f42129b58303bcf1e03723764a1702cbe98529802aad8514ee3cf',
+        '--node-url',
+        NODE_IP_ADDRESS_FOR_TESTING,
+    ])
+
+    assert PASSED_EXIT_FROM_COMMAND_CODE == result.exit_code
+    assert isinstance(json.loads(result.output), int)
+
+
+def test_get_balance_invalid_address():
+    """
+    Case: get a balance of an account by invalid address.
+    Expect: the following address is invalid error message.
+    """
+    invalid_address = '1120076ecf036e857f42129b5830'
+
+    runner = CliRunner()
+    result = runner.invoke(cli, [
+        'account',
+        'get-balance',
+        '--address',
+        invalid_address,
+        '--node-url',
+        NODE_IP_ADDRESS_FOR_TESTING,
+    ])
+
+    expected_error = {
+        'address': [
+            f'The following address `{invalid_address}` is invalid.',
+        ],
+    }
+
+    assert FAILED_EXIT_FROM_COMMAND_CODE == result.exit_code
+    assert dict_to_pretty_json(expected_error) in result.output
+
+
+def test_get_balance_without_node_url(mocker):
+    """
+    Case: get a balance of an account by address without passing node URL.
+    Expect: balance is returned.
+    """
+    balance_from_localhost = 13500
+
+    mock_account_get_balance = mocker.patch('cli.account.service.Account.get_balance')
+    mock_account_get_balance.return_value = return_async_value(balance_from_localhost)
+
+    runner = CliRunner()
+    result = runner.invoke(cli, [
+        'account',
+        'get-balance',
+        '--address',
+        '1120076ecf036e857f42129b58303bcf1e03723764a1702cbe98529802aad8514ee3cf',
+    ])
+
+    assert PASSED_EXIT_FROM_COMMAND_CODE == result.exit_code
+    assert isinstance(json.loads(result.output), int)
+    assert str(balance_from_localhost) in result.output
+
+
+def test_get_balance_invalid_node_url():
+    """
+    Case: get a balance of an account by passing invalid node URL.
+    Expect: the following node URL is invalid error message.
+    """
+    invalid_node_url = 'domainwithoutextention'
+
+    runner = CliRunner()
+    result = runner.invoke(cli, [
+        'account',
+        'get-balance',
+        '--address',
+        '1120076ecf036e857f42129b58303bcf1e03723764a1702cbe98529802aad8514ee3cf',
+        '--node-url',
+        invalid_node_url,
+    ])
+
+    expected_error = {
+        'node_url': [
+            f'The following node URL `{invalid_node_url}` is invalid.',
+        ],
+    }
+
+    assert FAILED_EXIT_FROM_COMMAND_CODE == result.exit_code
+    assert dict_to_pretty_json(expected_error) in result.output
+
+
+def test_get_balance_node_url_with_http():
+    """
+    Case: get a balance of an account by passing node URL with explicit HTTP protocol.
+    Expect: the following node URL contains protocol error message.
+    """
+    node_url_with_http_protocol = 'http://masternode.com'
+
+    runner = CliRunner()
+    result = runner.invoke(cli, [
+        'account',
+        'get-balance',
+        '--address',
+        '1120076ecf036e857f42129b58303bcf1e03723764a1702cbe98529802aad8514ee3cf',
+        '--node-url',
+        node_url_with_http_protocol,
+    ])
+
+    expected_error = {
+        'node_url': [
+            f'Pass the following node URL `{node_url_with_http_protocol}` without protocol (http, https, etc.).',
+        ],
+    }
+
+    assert FAILED_EXIT_FROM_COMMAND_CODE == result.exit_code
+    assert dict_to_pretty_json(expected_error) in result.output
+
+
+def test_get_balance_node_url_with_https():
+    """
+    Case: get a balance of an account by passing node URL with explicit HTTPS protocol.
+    Expect: the following node URL contains protocol error message.
+    """
+    node_url_with_https_protocol = 'https://masternode.com'
+
+    runner = CliRunner()
+    result = runner.invoke(cli, [
+        'account',
+        'get-balance',
+        '--address',
+        '1120076ecf036e857f42129b58303bcf1e03723764a1702cbe98529802aad8514ee3cf',
+        '--node-url',
+        node_url_with_https_protocol,
+    ])
+
+    expected_error = {
+        'node_url': [
+            f'Pass the following node URL `{node_url_with_https_protocol}` without protocol (http, https, etc.).',
+        ],
+    }
+
+    assert FAILED_EXIT_FROM_COMMAND_CODE == result.exit_code
+    assert dict_to_pretty_json(expected_error) in result.output