Add 404 Page
Adding a 404 page is easy. Simply create a page whose path matches the regex
/404*. Most often you’ll just want to create a React component page at
Gatsby ensures that your 404 page is built as
404.html as many static
hosting platforms default to using this as your 404 error page. If you’re
hosting your site another way, you’ll need to setup a custom rule to serve this
file for 404 errors.
When developing, Gatsby adds a default 404 page that overrides your custom 404 page. But you can still visit the exact url for your 404 page to verify it’s working as expected.