A rule determines whether the current caller may perform an action.
LET’S PICTURE IT
A club can ask for proof of membership before admitting someone. Merely naming a door “members only” does not enforce that policy.
SEE IT FOR YOURSELF
A valid counter call, step by stepStep 1 / 4
This example begins with count zero and a request to call increment(). No real contract is deployed.
This example begins with count zero and a request to call increment(). No real contract is deployed.Execution follows the code’s input and permission rules. A website button is not the access-control mechanism.The function reads zero, calculates zero plus one, and writes one to persistent storage.The accepted state contains count one. Later reads can inspect it. Events are emitted only if the code implements them.
Animated local teaching model. No wallet, RPC or live blockchain data. Some labels and hashes are abbreviated for readability.
State the allowed condition
A setting might be changeable only by an owner address or a configured role. The contract needs a code path that tests the relevant condition before allowing the sensitive effect.
The caller context matters
In a normal contract call, msg.sender identifies the immediate caller of that frame. Nested calls can make that caller another contract. A rule designed around the wrong identity can grant or deny access incorrectly.
Every sensitive path needs enforcement
Protecting one visible function is insufficient if another exposed path performs the same sensitive action without the check. Interfaces and comments help readers, but execution logic determines what is possible.
A failing check can revert
An unauthorized request may return custom error data or another revert form. The decoder can read supplied error bytes, but proving that access control is correct requires reviewing the complete implementation and state.