Error handling is a critical aspect of web application development. Flask provides mechanisms for handling errors and exceptions to ensure a smooth and user-friendly experience. In this guide, we'll explore how to handle errors and exceptions in Flask, including custom error pages, error handling decorators, and best practices.

Step 1: Custom Error Pages

Create custom error pages to display user-friendly error messages when exceptions occur. You can define custom error handlers for different HTTP error codes. Here's an example of creating a custom error page for a 404 error:

from flask import Flask, render_template
app = Flask(__name)
def page_not_found(e):
return render_template('404.html'), 404

In this example, the `@app.errorhandler` decorator is used to define a custom error handler for a 404 error. The error handler renders the '404.html' template and returns a 404 status code.

Step 2: Error Handling Decorators

Use error handling decorators to catch exceptions and handle them gracefully. For example, you can use the `@app.errorhandler` decorator to handle general exceptions and provide a fallback error page:

from flask import Flask, render_template
app = Flask(__name)
def handle_exception(e):
return render_template('error.html'), 500

This error handler catches all exceptions and renders the 'error.html' template with a 500 status code.

Step 3: Logging Errors

Implement error logging to record error details. Use a logging library to store error information in a file or send it to a remote logging service. Here's an example of setting up error logging in Flask:

import logging
app = Flask(__name)
# Configure logging to write to a file
file_handler = logging.FileHandler('error.log')

Step 4: Best Practices

When handling errors and exceptions in Flask, follow these best practices:

  • Provide informative error messages to users on custom error pages.
  • Use different error handlers for specific HTTP error codes (e.g., 404, 500).
  • Log errors to facilitate debugging and troubleshooting.
  • Handle exceptions gracefully to prevent application crashes.


Effective error handling is crucial to ensure a positive user experience and maintain the reliability of your Flask application. By following these steps and best practices, you can handle errors and exceptions in a way that makes your application more robust and user-friendly. Always strive to provide meaningful error messages and maintain thorough error logs.