How Do I Run a Flask Web Server?


Angela Bailey

Running a Flask web server is an essential skill for any web developer. Flask is a lightweight and flexible Python web framework that allows you to build dynamic web applications. In this tutorial, we will guide you through the steps of running a Flask web server.

Step 1: Installing Flask
Before you can run a Flask web server, you need to have Flask installed on your system. You can install Flask using pip, the package installer for Python. Open your terminal or command prompt and type the following command:

pip install flask

This will download and install Flask and its dependencies on your system.

Step 2: Setting up the Project
Once you have installed Flask, create a new directory for your project. Open your terminal or command prompt and navigate to the desired directory using the cd command. Then, create a new directory by typing:

mkdir my_flask_project

Navigate into the newly created directory using:

cd my_flask_project

Now, create a new Python file named This will serve as the entry point for your Flask application.

Step 3: Writing Your First Flask App
Open in a text editor or an integrated development environment (IDE). Import the necessary modules by adding the following lines of code at the beginning of your file:

# Importing required modules
from flask import Flask

# Creating an instance of the Flask class
app = Flask(__name__)

# Route decorator
def home():
return "Hello, World!"

# Running the app
if __name__ == '__main__':

Here’s what’s happening in this code:

1. We import the Flask module, which is necessary to create a Flask application. 2. We create an instance of the Flask class and assign it to the variable app. 3. We define a route decorator using the @app.route decorator.

This decorator tells Flask which URL should trigger our function. 4. The home() function is our view function for the homepage route (“/”). It returns the string “Hello, World!”. 5. Finally, we run the app using

Step 4: Running the Flask Web Server
To start your Flask web server, open your terminal or command prompt and navigate to your project directory (my_flask_project). Then, simply type:


Flask will start running on your local machine, and you will see output similar to this:

* Running on http://127.0.1:5000/ (Press CTRL+C to quit)

Now, open your web browser and navigate to http://localhost:5000/. You should see the text “Hello, World!” displayed on the page.

Congratulations! You have successfully run a Flask web server.

  • Note:
    • If you want to make changes to your Flask application, you need to stop the server by pressing CTRL+C in your terminal or command prompt.
    • To start the server again after making changes, use the same command: python

In Conclusion

In this tutorial, we walked through the process of running a Flask web server. We started by installing Flask using pip, then created a new project directory and wrote our first Flask application. Finally, we ran the Flask web server and accessed our application in the browser.

Flask is a powerful framework that allows you to build web applications with ease. With practice and exploration, you can unleash the full potential of Flask and create amazing web applications.

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