How can I tell whether an old redirect is still being used before I delete it?

Open SEO Settings → Redirects and look at Your redirects:

• Used counts how many times someone has followed that old link since the rule was created. A high number means the old address is still being shared.
• Last used shows when it was last followed.
• Rules marked auto were created for you automatically.

Use the Search a path… box to find a rule. If you are unsure, click Disable instead of Delete: the rule stays in the list (faded) and you can Enable it again if visitors start hitting broken pages. Once a disabled rule has clearly stopped mattering, click Delete.