• Difficulty - Medium
    Total Plays - 6
    Allowed Time - 10 sec
    Best time - 3.892

    Which Solidity keyword prevents state variable shadowing?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    The override keyword forces explicit acknowledgment when a derived contract replaces a parent variable or function. This prevents accidental state variable shadowing in inheritance hierarchies, which can otherwise lead to subtle storage corruption bugs.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 12
    Allowed Time - 10 sec
    Best time - 3.307

    Why should developers avoid using tx.origin for authentication?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Attackers can trick users into calling a malicious contract. That contract then makes a call where tx.origin equals the victim’s address. This bypasses access control and leads to unauthorized actions.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 13
    Allowed Time - 10 sec
    Best time - 1.493

    Why are fallback functions dangerous?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Fallback functions run automatically when unknown calls or plain ETH are sent. If they contain external calls or heavy logic, attackers can trigger recursion or re-entrancy. They must be kept minimal and safe.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 12
    Allowed Time - 10 sec
    Best time - 1.974

    Why can abi.encodePacked cause issues?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    encodePacked removes padding, which can produce identical byte sequences for different inputs. When combined with hashing, this may cause collisions. Using abi.encode is safer for multi-field data.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 14
    Allowed Time - 10 sec
    Best time - 4.554

    What makes nested delegatecalls dangerous?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Each delegatecall runs in the caller’s storage space, so nesting them multiplies the chances of overwriting incorrect slots. This breaks upgradeability guarantees and corrupts state. Auditors treat deep delegatecall chains as red flags.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 17
    Allowed Time - 10 sec
    Best time - 2.746

    Why do upgradeable contracts avoid constructors?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Constructors run only during deployment and do not execute through proxies. Using an initializer ensures state is properly set through proxy calls. The entire proxy pattern relies on replacing constructors with explicit initialization.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 21
    Allowed Time - 10 sec
    Best time - 1.062

    Why avoid multiple SSTOREs in a function?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    SSTORE is one of the most expensive operations and repeating it unnecessarily multiplies costs. Caching values into memory and writing once dramatically optimizes gas. This is foundational in gas-sensitive protocols.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 18
    Allowed Time - 10 sec
    Best time - 1.746

    Why is assert() dangerous in production?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    assert() triggers a Panic error and is intended only for internal guarantees. If it fires in production, it indicates a compiler or logic bug. Developers should use require() for user-facing validation.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 17
    Allowed Time - 10 sec
    Best time - 1.487

    Why is msg.value validation kept at the top of functions?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Validating msg.value early ensures no state mutation occurs before detecting invalid ether transfers. This prevents partially updated storage on failure, preserving atomicity. It aligns with checks-effects-interactions
    Leaderboard
  • Difficulty - Medium
    Total Plays - 13
    Allowed Time - 10 sec
    Best time - 6.381

    What does a selector collision indicate?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Selector collisions occur when different function signatures hash to the same first 4 bytes. This leads to unintended dispatching and silent bugs. It’s especially dangerous in diamond proxies and minimal routers.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 9
    Allowed Time - 10 sec
    Best time - 1.153

    What makes fallback functions error-prone?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Fallbacks receive raw calldata without predefined structure, forcing developers to manually decode and validate inputs. Any mistake leads to reentrancy or mis-routing. They must be extremely minimal.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 14
    Allowed Time - 10 sec
    Best time - 4.927

    Why do storage reads cost more than memory reads?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Storage accesses require Merkle-Patricia proof validation at the state level. This makes SLOAD one of the most expensive operations in Solidity. Caching values into memory significantly reduces repeated cost.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 7
    Allowed Time - 10 sec
    Best time - 6.303

    Why are external loops discouraged?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Unbounded loops that depend on storage or user-controlled arrays can exhaust gas and render functions uncallable. Attackers can intentionally cause denial-of-service through loop amplification. Good design avoids external iteration
    Leaderboard
  • Difficulty - Medium
    Total Plays - 7
    Allowed Time - 10 sec
    Best time - 2.699

    Why avoid comparing strings on-chain?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    String comparison requires hashing or byte-by-byte checks, both of which are expensive in the EVM model. It also introduces risk when mixed with packed encodings. Developers instead rely on enums or hashed IDs.
    Leaderboard
  • Difficulty - Medium
    Total Plays - 8
    Allowed Time - 10 sec
    Best time - 10

    What makes memory expansion expensive?

    Tip: Click "Play" to reveal options and start playing.

    #A
    #B
    #C
    #D
    Explanation:
    Memory follows a quadratic cost function, meaning costs rise rapidly as the memory footprint grows. Careless array allocations can suddenly inflate execution cost. This is a frequent root cause of gas blowups in audits.
    Leaderboard