Invalid authenticity token Rails CSRF

Why This Happens

In Ruby on Rails, the csrf token is missing or invalid. This is one of the most common Ruby on Rails errors developers encounter. Understanding the root cause helps you fix it quickly and prevent it from recurring.

The Problem

<form method='post'>
  <button>Submit</button>
</form>

The Fix

<%= form_with do |f| %>
  <%= f.submit %>
<% end %>

Step-by-Step Fix

1. 1

   Identify the error

   Look at the error message: ActionController::InvalidAuthenticityToken. This tells you exactly what went wrong.

2. 2

   Find the cause

   Check the stack trace to find which line of your Ruby on Rails code triggered this error.

3. 3

   Apply the fix

   Use the corrected code pattern shown above. Test to confirm the error is resolved.