How to Fix Method Not Allowed Error in Flask

The Method Not Allowed error in Flask happens when a route does not accept the HTTP method used by the client, like POST or GET. To fix it, specify the allowed methods in your route decorator using methods=['GET', 'POST'] so Flask knows which requests to accept.

Why This Happens

This error occurs because Flask routes only accept certain HTTP methods by default. If a client sends a request with a method not listed in the route's allowed methods, Flask responds with a 405 Method Not Allowed error.

For example, if your route only accepts GET requests but the client sends a POST request, Flask will reject it.

python

from flask import Flask, request

app = Flask(__name__)

@app.route('/submit')
def submit():
    return 'Form submitted!'

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

Output

Method Not Allowed (405) error when sending POST request to /submit

The Fix

To fix this, explicitly tell Flask which HTTP methods your route should accept by adding the methods parameter to the @app.route decorator. For example, to accept both GET and POST requests, use methods=['GET', 'POST'].

This way, Flask will allow POST requests to your route and avoid the 405 error.

python

from flask import Flask, request

app = Flask(__name__)

@app.route('/submit', methods=['GET', 'POST'])
def submit():
    if request.method == 'POST':
        return 'Form submitted via POST!'
    return 'Send a POST request to submit.'

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

Output

When sending POST request to /submit: 'Form submitted via POST!'
When sending GET request to /submit: 'Send a POST request to submit.'

Prevention

Always specify the HTTP methods your routes should accept to avoid this error. Use methods in the route decorator even if you expect only POST or PUT requests.

Use tools like linters or code reviews to check that routes have correct method declarations. Testing your API endpoints with tools like Postman or curl helps catch method mismatches early.

Related Errors

404 Not Found: Happens when the route URL does not exist. Check your route paths carefully.

405 Method Not Allowed: Happens when the HTTP method is not allowed on the route. Fix by adding methods parameter.

500 Internal Server Error: Happens due to server-side bugs. Check your code logic and error logs.

Key Takeaways

Specify allowed HTTP methods in Flask routes using the methods parameter.

Method Not Allowed error means the HTTP method used is not accepted by the route.

Test your routes with different HTTP methods to catch errors early.

Use linters and code reviews to ensure routes declare correct methods.

Check related errors like 404 and 500 to diagnose routing issues.