How to Get Warned Before Your Tool Breaks
The whole point of Durability Notifier is to stop you from swinging a pickaxe until it shatters. Here is how to set it up so you actually get the warning in time.
Pick a Threshold That Suits You
Open the mod's config menu and raise the Percentage value above the default of 10 if you want more breathing room. A higher percentage means the mod starts warning you while the tool still has plenty of durability left, giving you time to swap it out or repair it. If you find the warnings annoying, lower the value so they only fire when the tool is genuinely close to breaking.
Choose Your Notification Method
Enable PlaySound to hear a cue whenever you try to use a low-durability tool. Enable SendMessage if you would rather see a text notification. You can turn on both at once if you want a sound and a message together.
Optional Safety Net
If you keep forgetting to swap tools, enable GiveFatigue. When the tool hits its limit, you receive Mining Fatigue, which slows your mining and stops you from accidentally destroying the tool. Remember this feature does not work on vanilla servers, so rely on sound or messages there instead.
With a sensible percentage and at least one notification enabled, you will always know when it is time to repair or replace your gear.