Reading an Audit Contest Scope Like an Auditor: Invariants First, Code Second

The first time I audited seriously, I opened the biggest contract in the repo and started reading line one. Two hours later I had a headache and zero findings. I had memorized how the code worked without ever asking what it was supposed to guarantee. That is backwards, and it took me a while to unlearn it. Now I do not read Solidity first. I read the scope, and before I look at a single function body I write down what must always be true. Bugs are violations of those truths. If you do not know the truths, you are just admiring the code. Step one: write the invariants before you read An invariant is a property the protocol claims will always hold, no matter who calls what in what order. For a contest, I start with money and control, because that is where severity lives. Two questions cover most of it: Who can move funds, and under what conditions? What must always hold about the accounting? For a lending-pool-shaped protocol my starting invariant list looks like this, written in plain language before I care how any of it is implemented: The sum of all user deposits minus all borrows equals the pool's available liquidity plus outstanding debt. Accounting must reconcile. A user can only withdraw up to their own balance, never more, never someone else's. A position can only be liquidated when it is actually under the health threshold. Interest accrues monotonically, it never goes backwards in a way that lets someone repay less than they owe. Only the borrower, or a liquidator on an unhealthy position, can reduce a debt. Nobody except governance can change interest rate parameters or the oracle. Notice none of that mentions a function name. These are the promises. Now my job for the rest of the contest is simple to state: find an ordering of calls that breaks one of these. Step two: map the external entry points Funds do not teleport. Something has to be called from outside for state to change. So I list every externally reachable function, because the attack surface is