Use jsonify() instead of json.dumps() in Flask

When developing APIs with Flask, you will often need to send JSON responses. Although both jsonify() and json.dumps() can be used for this, Flask provides the jsonify() helper function for a more seamless experience.

What is jsonify()

jsonify() is a built-in Flask function that converts Python dictionaries and objects into JSON response objects. It also automatically sets:

• The correct Content-Type header (application/json)
• Proper HTTP status codes (default: 200 OK)

This makes jsonify() more convenient than manually using json.dumps() with Response.

Syntax of jsonify()

jsonify(*args, **kwargs)

• args: Single list or dict (will be JSON-encoded)
• kwargs: Named key-value pairs, returned as JSON object

Examples of jsonify()

Let's look at some of the examples and use cases for jsonify().

Example 1: Using jsonify() Without Arguments

You can use jsonify() without any arguments, in this case it will return an empty JSON response object with a default status code of 200 (OK) and a default content type of application/json.

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/api/users')
def get_users():
    return jsonify()

Output:

{}

Explanation:

• This creates an empty JSON response ({}) with HTTP status 200 OK.
• Useful for routes that acknowledge a request without returning data.

Example 2: Using jsonify() With Arguments

In this example, we are calling jsonify() with a single positional argument (the list of user objects), as well as two keyword arguments with status and mimetype.

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/api/users')
def get_users():
    users = [{'id': 1, 'username': 'Prajjwal'}, {'id': 2, 'username': 'Kareena'}]
    return jsonify(users, status=200, mimetype='application/json')

Output:

{

"users": [

{"id": 1, "username": "Alice"},

{"id": 2, "username": "Bob"}

]

}

Explanation:

• A list of user dictionaries is passed as a named argument (users=...).
• jsonify() wraps it as a JSON object.

Full Flask App Using jsonify()

In this example, we have a Flask app with a route that returns a list of user objects. When a client makes a request to this route, the get_users() function is executed and the list of user objects is converted to a JSON response object using the jsonify() function. This JSON response object is then sent back to the client.

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/')
def get_users():
    print("Returning JSON data using jsonify()")
    users = [
        {'id': 1, 'username': 'sweety'},
        {'id': 2, 'username': 'pallavi'}
    ]
    return jsonify({'users': users})

if __name__ == '__main__':
    app.run(debug=True)

Output:

Explanation:

• '/' route returns a JSON object with a list of users.
• debug=True enables live reloading and error reporting during development.
• jsonify() handles all the boilerplate like content-type and encoding.

json.dumps() method in Flask

In contrast, if you were to use the json.dumps() function, you would need to convert the list of user objects to a JSON-formatted string yourself, and then set the appropriate response headers and return the response to the client manually:

Using jsonify() is generally easier and more convenient than using json.dumps(), so it's recommended to use jsonify() whenever possible in Flask apps.

from flask import Flask, Response
import json

app = Flask(__name__)

@app.route('/api/users')
def get_users():
    users = [{'id': 1, 'username': 'sweety'},
             {'id': 2, 'username': 'pandey'}]
    response = Response(
        response=json.dumps(users),
        status=200,
        mimetype='application/json'
    )
    return response


if __name__ == "__main__":
    app.run()

Visit URL: http://127.0.0.1:5000/api/users

Why to Use jsonify() instead of json.dumps()

There are several reasons why it is recommended to use the jsonify() function instead of the json.dumps() function in Flask apps:

• Automatically sets proper headers
• Simple and readable syntax
• Reduces manual errors
• Flask-native and tightly integrated
• Ideal for RESTful APIs and AJAX responses

Related Articles:

• Flask
• json.dumps()