Most homeowners never think about the anode rod inside a water heater tank until the tank starts to smell or rust. The rod is a metal piece, usually threaded into the top of the tank, that corrodes on purpose so the steel tank wall does not. Once it is spent, the tank has no protection. Checking it is a real decision. For someone comfortable with a socket and a shutoff, it can be a short job. For someone facing a stuck fitting or a gas unit, it can go wrong quickly.
Sort the job before you touch anything
Ask three questions first. Can you reach the top of the tank with a socket and a long breaker bar, with enough room above it to pull the rod straight up? Can you shut off the power or gas and the cold water supply to the heater? Do you know where the drain valve is and where the water will go when you open it? If any answer is no, that is your first sign to call a plumber.
What you can do yourself
Looking at the rod is the easy part. Turn off the heater, close the cold supply valve, and open a hot faucet somewhere in the house to relieve pressure. Attach a hose to the drain valve, open it, and let enough water out to drop below the rod's fitting. Remove the top cover if your model has one, then loosen the rod with a socket. Pull it out slowly. A rod that is mostly bare core wire, or worn down to a short stub, has done its job. A heavy crust or a rough, pitted surface tells you the same thing. Write down what you saw so the next check starts from facts.
When to hand it to a plumber
Stop and call if the rod will not move and you are leaning hard on a long bar, if the fitting starts to weep, if the tank threads look damaged, if the heater runs on gas and you are not comfortable relighting it, or if the tank sits with no clearance above it. A plumber can also check whether a different rod type suits your water. Ask them to explain the reason for the choice so you can compare it with what the next person recommends.
Before you close it up
If you replaced the rod, check the fitting for leaks after the tank refills, and only then restore power or gas. If you did not replace it, record what you found and what you plan to check next time.