prevent-mint-front-running

Prevent mint front-running

Bots watch the mempool and buy scarce mints the moment a transaction is visible, sniping allowlist spots and rare token ids before a human's transaction lands.

Procedure

1. Identify what a bot can predict: an open mint() with no allowlist, and token ids assigned by totalSupply(). If the id is knowable, bots can target a specific rare id.

2. Enforce the allowlist on-chain with a Merkle root or signature so a bot that is not listed cannot mint even after seeing the transaction:

   cast call $NFT "merkleRoot()(bytes32)" --rpc-url $RPC
   

3. Submit through a private or protected endpoint so the transaction is not visible before inclusion:

   cast send $NFT "mint(uint256)" 1 --private-key $KEY --rpc-url $PROTECT_RPC
   

4. Randomize token id assignment after mint time via a committed reveal (see commit-reveal), making id sniping pointless.

5. Consider require(tx.origin == msg.sender) only with eyes open — it blocks naive bot contracts but not a bot that owns an EOA.

6. Set a per-transaction and per-wallet cap so one bot cannot take an entire phase:

   grep -nE 'maxMintPerTx|maxPerWallet|require\(.*minted' src/*.sol
   

7. Add a commit-delay: commit() then revealMint() two blocks later, so mempool sniping gains nothing.

8. Race-test on a fork:

   forge test --match-test testSniping --fork-url $RPC -vvvv
   

Pitfalls

• A public RPC rebroadcasts your transaction to the general mempool, defeating a private submission.
• Bots also watch the pending set and simulate; tx.origin checks do not stop EOAs.
• Reveal-after-mint removes id sniping but not supply sniping — keep the per-wallet cap too.
• A gas price set lower than the bots' guarantees your transaction is delayed, not protected.
• Accepting deposits before the allowlist check lets a bot's transaction reserve slots it later abandons.

Verification

forge test --match-test testSniping --fork-url $RPC -vvvv

Pass: a bot contract minting with a forged or absent proof reverts and the per-wallet cap holds under concurrent calls. Report the protection used (allowlist / private mempool / reveal) and the cap.