I judge a toilet by how predictable it is. A healthy toilet does the same thing every time. Once it starts doing weird “sometimes” behaviour, I pay attention because small issues often turn into water waste or leaks. The biggest sign for repair is a toilet that keeps running after a flush, or one that randomly refills when nobody has used it. That often points to a worn flush valve seal or a float issue, and it can quietly add a lot to your water bill. I only realised how much when I did the food colouring test. I put a few drops of colouring in the cistern, waited 10 to 15 minutes without flushing, and saw colour creep into the bowl. That told me water was leaking through constantly.
Other repair signs include weak flushing, gurgling noises, water pooling at the base, or a cistern that takes ages to refill. I also watch for hairline cracks in the bowl or cistern. Even tiny cracks can worsen with temperature changes and vibrations, especially in older bathrooms. Replacement starts to make more sense when repairs keep repeating, parts are hard to match, or the porcelain is cracked. I also consider replacement if the toilet is very old and uses a lot of water per flush, because efficiency upgrades can pay off over time. If you're exploring this subject Endpoint Plumbing offers some valuable information. Come to think of it, if you ever see water at the base, I treat it as urgent, because it can mean a failed wax seal or a hidden crack that could damage flooring.
