diff --git a/.flake8 b/.flake8
new file mode 100644
index 00000000..5b9686af
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,20 @@
+[flake8]
+max-line-length = 89
+
+exclude =
+    build
+    modules
+    dist
+    docs
+    coverage.xml
+    reana_job_controller.egg-info
+    .*/
+    env/
+    .git
+    __pycache__
+
+ignore = E203, E231, E266, E501, W503, F403, F401
+
+max-complexity = 18
+
+select = B,C,E,F,W,T4,B9
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 85fcdc88..3922e2c6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,6 +29,23 @@ jobs:
           - name: Check Python code formatting
             run: ./run-tests.sh --check-black
 
+    lint-flake8:
+      runs-on: ubuntu-20.04
+      steps:
+        - name: Checkout
+          uses: actions/checkout@v2
+
+        - name: Setup Python
+          uses: actions/setup-python@v2
+          with:
+            python-version: 3.8
+
+        - name: Check compliance with pep8, pyflakes and circular complexity
+          run: |
+            pip install --upgrade pip
+            pip install flake8
+            ./run-tests.sh --check-flake8
+
     lint-pydocstyle:
       runs-on: ubuntu-20.04
       steps:
diff --git a/MANIFEST.in b/MANIFEST.in
index 90aef00f..93e85a0f 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -12,6 +12,7 @@ include *.sh
 include *.txt
 include *.yaml
 include *.yml
+include .flake8
 include pytest.ini
 include docs/requirements.txt
 include docs/cmd_list.txt
diff --git a/reana_client/api/client.py b/reana_client/api/client.py
index 830512bf..49c56272 100644
--- a/reana_client/api/client.py
+++ b/reana_client/api/client.py
@@ -58,7 +58,7 @@ def ping(access_token):
         if e.response.status_code == 403:
             return {"status": "ERROR: INVALID ACCESS TOKEN", "error": True}
         raise Exception(e.response)
-    except Exception as e:
+    except Exception:
         return {"status": "ERROR: INVALID SERVER", "error": True}
 
 
diff --git a/reana_client/cli/cwl_runner.py b/reana_client/cli/cwl_runner.py
index 25dc1339..999211a9 100644
--- a/reana_client/cli/cwl_runner.py
+++ b/reana_client/cli/cwl_runner.py
@@ -157,7 +157,7 @@ def cwl_runner(ctx, quiet, outdir, basedir, processfile, jobfile, access_token):
                 # click.echo(response['status'])
                 break
         try:
-            out = re.search("success{[\S\s]*", logs).group().replace("success", "")
+            out = re.search(r"success{[\S\s]*", logs).group().replace("success", "")
             import ast
             import json
 
@@ -165,7 +165,7 @@ def cwl_runner(ctx, quiet, outdir, basedir, processfile, jobfile, access_token):
         except AttributeError:
             logging.error("Workflow execution failed")
             sys.exit(1)
-        except Exception as e:
+        except Exception:
             logging.error(traceback.format_exc())
             sys.exit(1)
         sys.stdout.write(json_output)
@@ -175,7 +175,7 @@ def cwl_runner(ctx, quiet, outdir, basedir, processfile, jobfile, access_token):
     except HTTPServerError as e:
         logging.error(traceback.print_exc())
         logging.error(e)
-    except Exception as e:
+    except Exception:
         logging.error(traceback.print_exc())
 
 
diff --git a/reana_client/cli/files.py b/reana_client/cli/files.py
index 2eb91bb0..61b929b5 100644
--- a/reana_client/cli/files.py
+++ b/reana_client/cli/files.py
@@ -352,7 +352,7 @@ def delete_files(ctx, workflow, filenames, access_token):  # noqa: D301
     Examples:\n
     \t $ reana-client rm -w myanalysis.42 data/mydata.csv \n
     \t $ reana-client rm -w myanalysis.42 'code/\*'
-    """
+    """  # noqa: W605
     from reana_client.api.client import delete_file
 
     logging.debug("command: {}".format(ctx.command_path.replace(" ", ".")))
@@ -450,7 +450,7 @@ def move_files(ctx, source, target, workflow, access_token):  # noqa: D301
                     err=True,
                 )
                 sys.exit(1)
-            response = mv_files(source, target, workflow, access_token)
+            mv_files(source, target, workflow, access_token)
             click.echo(
                 click.style(
                     "{} was successfully moved to {}.".format(source, target),
diff --git a/reana_client/cli/utils.py b/reana_client/cli/utils.py
index 71e4b3e3..a77d5af3 100644
--- a/reana_client/cli/utils.py
+++ b/reana_client/cli/utils.py
@@ -177,7 +177,7 @@ def key_value_to_dict(ctx, param, value):
     """
     try:
         return dict(op.split("=") for op in value)
-    except ValueError as err:
+    except ValueError:
         click.secho(
             '==> ERROR: Input parameter "{0}" is not valid. '
             'It must follow format "param=value".'.format(" ".join(value)),
diff --git a/reana_client/cli/workflow.py b/reana_client/cli/workflow.py
index 44ecd4a8..45c3f4d3 100644
--- a/reana_client/cli/workflow.py
+++ b/reana_client/cli/workflow.py
@@ -111,7 +111,7 @@ def workflow_execution_group(ctx):
 @add_pagination_options
 @check_connection
 @click.pass_context
-def workflow_workflows(
+def workflow_workflows(  # noqa: C901
     ctx,
     sessions,
     _filter,
@@ -587,7 +587,7 @@ def workflow_restart(
 @check_connection
 @click.option("-v", "--verbose", count=True, help="Set status information verbosity.")
 @click.pass_context
-def workflow_status(
+def workflow_status(  # noqa: C901
     ctx, workflow, _filter, output_format, access_token, verbose
 ):  # noqa: D301
     """Get status of a workflow.
@@ -945,7 +945,7 @@ def workflow_stop(ctx, workflow, force_stop, access_token):  # noqa: D301
     if workflow:
         try:
             logging.info("Sending a request to stop workflow {}".format(workflow))
-            response = stop_workflow(workflow, force_stop, access_token)
+            stop_workflow(workflow, force_stop, access_token)
             click.secho(get_workflow_status_change_msg(workflow, "stopped"), fg="green")
         except Exception as e:
             logging.debug(traceback.format_exc())
@@ -1097,9 +1097,7 @@ def workflow_delete(
     if workflow:
         try:
             logging.info("Connecting to {0}".format(get_api_url()))
-            response = delete_workflow(
-                workflow, all_runs, hard_delete, workspace, access_token
-            )
+            delete_workflow(workflow, all_runs, hard_delete, workspace, access_token)
             if all_runs:
                 message = "All workflows named '{}' have been deleted.".format(
                     workflow.split(".")[0]
diff --git a/run-tests.sh b/run-tests.sh
index de731b73..f69bd458 100755
--- a/run-tests.sh
+++ b/run-tests.sh
@@ -21,6 +21,10 @@ check_black () {
     black --check .
 }
 
+check_flake8 () {
+    flake8 .
+}
+
 check_pydocstyle () {
     pydocstyle reana_client
 }
@@ -55,6 +59,7 @@ check_pytest () {
 check_all() {
     check_script
     check_black
+    check_flake8
     check_pydocstyle
     check_manifest
     check_cli_cmds
@@ -73,6 +78,7 @@ do
     case $arg in
         --check-shellscript) check_script;;
         --check-black) check_black;;
+        --check-flake8) check_flake8;;
         --check-pydocstyle) check_pydocstyle;;
         --check-manifest) check_manifest;;
         --check-cli-cmds) check_cli_cmds;;
diff --git a/setup.py b/setup.py
index 0ea2a8d5..564a414f 100644
--- a/setup.py
+++ b/setup.py
@@ -60,7 +60,7 @@
 
 # Get the version string. Cannot be done with import!
 with open(os.path.join("reana_client", "version.py"), "rt") as f:
-    version = re.search('__version__\s*=\s*"(?P<version>.*)"\n', f.read()).group(
+    version = re.search(r'__version__\s*=\s*"(?P<version>.*)"\n', f.read()).group(
         "version"
     )
 
diff --git a/tests/test_cli_workflows.py b/tests/test_cli_workflows.py
index 3568e763..5d0cc037 100644
--- a/tests/test_cli_workflows.py
+++ b/tests/test_cli_workflows.py
@@ -487,7 +487,7 @@ def test_run(
     with runner.isolated_filesystem():
         with open(reana_workflow_schema, "w") as f:
             f.write(create_yaml_workflow_schema)
-        result = runner.invoke(
+        runner.invoke(
             cli, ["run", "-t", reana_token, "-f", reana_workflow_schema],
         )
     assert workflow_create_mock.called is True