Writing Plugins

You can extend FlexMeasures with functionality like UI pages or CLI functions.

A FlexMeasures plugin works as a Flask Blueprint.


We’ll use this to allow for custom forecasting and scheduling algorithms, as well.

How it works

Use the config setting FLEXMEASURES_PLUGIN_PATHS to point to your plugin(s).

Here are the assumptions FlexMeasures makes to be able to import your Blueprint:

  • The plugin folder contains an __init__.py file.

  • In that file, you define a Blueprint object (or several).

We’ll refer to the plugin with the name of your plugin folder.


Here is a showcase file which constitutes a FlexMeasures plugin called our_client.

  • We demonstrate adding a view, which can be rendered using the FlexMeasures base templates.

  • We also showcase a CLI function which has access to the FlexMeasures app object. It can be called via flexmeasures our_client test.

We first create the file <some_folder>/our_client/__init__.py. This means that our_client is the plugin folder and becomes the plugin name.

With the __init__.py below, plus the custom Jinja2 template, our_client is a complete plugin.

__version__ = "2.0"

from flask import Blueprint, render_template, abort

from flask_security import login_required
from flexmeasures.ui.utils.view_utils import render_flexmeasures_template

our_client_bp = Blueprint('our_client', __name__,

# Showcase: Adding a view

def metrics():
    msg = "I am a FlexMeasures plugin !"
    # Note that we render via the in-built FlexMeasures way
    return render_flexmeasures_template(

# Showcase: Adding a CLI command

import click
from flask import current_app
from flask.cli import with_appcontext

our_client_bp.cli.help = "Our client commands"

def oc_test():
    print(f"I am a CLI command, part of FlexMeasures: {current_app}")


You can overwrite FlexMeasures routing in your plugin. In our example above, we are using the root route /. FlexMeasures registers plugin routes before its own, so in this case visiting the root URL of your app will display this plugged-in view (the same you’d see at /my-page).


The __version__ attribute on our module is being displayed in the standard FlexMeasures UI footer, where we show loaded plugins. Of course, it can also be useful for your own maintenance.

The template would live at <some_folder>/our_client/templates/my_page.html, which works just as other FlexMeasures templates (they are Jinja2 templates):

{% extends "base.html" %}

{% set active_page = "my-page" %}

{% block title %} Our client dashboard {% endblock %}

{% block divs %}

    <!-- This is where your custom content goes... -->

    {{ message }}

{% endblock %}


Plugin views can also be added to the FlexMeasures UI menu ― just name them in the config setting FLEXMEASURES_MENU_LISTED_VIEWS. In this example, add my-page. This also will make the active_page setting in the above template useful (highlights the current page in the menu).

Starting the template with {% extends "base.html" %} integrates your page content into the FlexMeasures UI structure. You can also extend a different base template. For instance, we find it handy to extend base.html with a custom base template, to extend the footer, as shown below:

{% extends "base.html" %}

{% block copyright_notice %}

Created by <a href="https://seita.nl/">Seita Energy Flexibility</a>,
in cooperation with <a href="https://ourclient.nl/">Our Client</a>
<script>var CurrentYear = new Date().getFullYear(); document.write(CurrentYear)</script>.

{% endblock copyright_notice %}

We’d name this file our_client_base.html. Then, we’d extend our page template from our_client_base.html, instead of base.html.

Using other code files in your plugin

Say you want to include other Python files in your plugin, importing them in your __init__.py file. This can be done if you put the plugin path on the import path. Do it like this in your __init__.py:

import os
import sys

HERE = os.path.dirname(os.path.abspath(__file__))
sys.path.insert(0, HERE)

from my_other_file import my_function

Using a custom favicon icon

The favicon might be an important part of your customisation. You probably want your logo to be used.

First, your blueprint needs to know about a folder with static content (this is fairly common ― it’s also where you’d put your own CSS or JavaScript files):

our_client_bp = Blueprint(

Put your icon file in that folder. The exact path may depend on how you set your plugin directories up, but this is how a blueprint living in its own directory could work.

Then, overwrite the /favicon.ico route which FlexMeasures uses to get the favicon from:

from flask import send_from_directory

def favicon():
    return send_from_directory(

Here we assume your favicon is a PNG file. You can also use a classic .ico file, then your mime type probably works best as image/x-icon.

Validating arguments in your CLI commands with marshmallow

Arguments to CLI commands can be validated using marshmallow. FlexMeasures is using this functionality (via the MarshmallowClickMixin class) and also defines some custom field schemas. We demonstrate this here, and also show how you can add your own custom field schema:

from datetime import datetime
from typing import Optional

import click
from flexmeasures.data.schemas.times import AwareDateTimeField
from flexmeasures.data.schemas.utils import MarshmallowClickMixin
from marshmallow import fields

class CLIStrField(fields.Str, MarshmallowClickMixin):
    String field validator, made usable for CLI functions.
    You could also define your own validations here.

    help="(Required) Where we meet",
    type=AwareDateTimeField(format="iso"),  # FlexMeasures already made this field suitable for CLI functions
    help="[Optional] When we meet (expects timezone-aware ISO 8601 datetime format)",
def schedule_meeting(
    where: str,
    when: Optional[datetime] = None,
    print(f"Okay, see you {where} on {when}.")

Customising the login page teaser

FlexMeasures shows an image carousel next to its login form (see ui/templates/admin/login_user.html).

You can overwrite this content by adding your own login template and defining the teaser block yourself, e.g.:

{% extends "admin/login_user.html" %}

{% block teaser %}

    <h1>Welcome to my plugin!</h1>

{% endblock %}

Place this template file in the template folder of your plugin blueprint (see above). Your template must have a different filename than “login_user”, so FlexMeasures will find it properly!

Finally, add this config setting to your FlexMeasures config file (using the template filename you chose, obviously):

SECURITY_LOGIN_USER_TEMPLATE = "my_user_login.html"