Smart Contract Gotchas: What I Wish I Knew Before Auditing Solidity Code + Bonus

Auditing smart contracts can feel deceptively simple. But once you’re in, you realize how many tiny mistakes can cost millions. Here’s what I wish I knew before I started digging into Solidity code.

1. Don’t Trust the Obvious:
If something can be expl…


This content originally appeared on DEV Community and was authored by Vadym

Auditing smart contracts can feel deceptively simple. But once you're in, you realize how many tiny mistakes can cost millions. Here’s what I wish I knew before I started digging into Solidity code.

1. Don’t Trust the Obvious:
If something can be exploited, someone will exploit it. That simple-looking transferFrom()? It’s a security risk without proper checks. Always think like an attacker.

2. Reentrancy Isn’t Just a Buzzword:
The DAO hack wasn’t a one-off—reentrancy bugs still show up in modern code. Updating state after external calls is a dangerous habit. Protect against it with logic, not just nonReentrant.

3. Math Is Never Innocent:
Solidity math can bite you hard, especially with overflows or rounding errors. Even in Solidity 0.8+, bad division or type casting can silently break logic. Always double-check calculations.

4. Ownable ≠ Safe by Default:
Using Ownable is fine—forgetting to transfer ownership isn’t. I’ve seen contracts deployed with critical admin functions left open. Always verify control flow and access after deployment.

5. Gas Optimization Can Break Things:
Saving gas is great, but not if it costs you correctness. Rearranged storage or removed checks might boost performance—but often create silent bugs. First get it right, then get it cheap.

6. Tools Help, But They Miss Things:
Slither, MythX, Foundry—they're useful, but not magic. Static analysis won’t catch logic bugs or business rule violations. Manual review is still your best defense.

7. Test Like a Hacker, Not a User:
Most bugs don’t show up under “normal” conditions. Use edge cases, fuzzing, weird sequences—try to break things. If your test suite only checks happy paths, it’s not an audit, it’s a nap.

Bonus: Audit Checklist
Access control verified

  • No unguarded external calls
  • Math checks in place
  • Upgradeability logic secure (if applicable)
  • Events emitted for critical state changes
  • Tests cover both expected + malicious behavior

In the end:
Solidity is safer than it used to be, but smart contracts still demand paranoia. The biggest risk isn’t the code - it’s the false sense of security around it.


This content originally appeared on DEV Community and was authored by Vadym


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