Block 0 Sniper Explained: Same-Block Token Launch Buys

Q: Why didn't my block 0 snipe land even though I set high gas?

On Ethereum, standard gas settings (maxFeePerGas) in MetaMask do not bundle your transaction behind a pending mempool transaction. Furthermore, if the developer sent their openTrading() transaction via a private RPC (like Flashbots Protect), it never appeared in the public mempool, meaning external bots can only buy in Block 1 (launchBlock + 1).

Q: Do I pay gas if my Block 0 Flashbots bundle doesn't win?

No. When your block 0 sniper submits via eth_sendBundle with a conditional builder payment and minimum token output check, any bundle that gets outbid or reverts is dropped by the block builder before inclusion, costing you 0 ETH in gas.

By Merunas Grincalaitis, founder of MEV DAO and a developer who builds MEV, sniping and trading bots on Ethereum. Last updated: October 2026.

TL;DR: A block 0 sniper on Ethereum is a bot that detects a token developer's pending liquidity-addition (addLiquidityETH) or trading-enable (openTrading) transaction in the mempool and bundles its own buy transaction directly behind it inside the exact same block (Block 0) via private MEV-Boost builders like Flashbots, Titan, and Beaverbuild. Winning a same block buy requires fast pending-transaction decoding, local eth_callBundle honeypot simulation, and a competitive block.coinbase builder bribe.

When traders look up what is a crypto sniper or how a block 0 sniper manages to buy millions of tokens at the exact second a Uniswap pool opens, they often assume the buyer had insider access to the contract deployer. In reality, unless the developer submitted their launch transaction privately, every public liquidity addition sits in the Ethereum mempool for 1 to 12 seconds before a block is proposed.

That window is all a token launch sniper needs to construct an atomic bundle [developer_tx, sniper_buy_tx] so the buy executes immediately after trading opens in Block 0. Here is how block-0 sniping works under the hood on Ethereum mainnet, how block builders rank competing snipers, and how to avoid the deadblocks and blacklist traps that wipe out naive bots.

What is Block 0 on an Ethereum token launch?

In Ethereum sniping terminology, Block 0 is the specific block number in which a token transitions from untradable to tradable on a decentralized exchange like Uniswap V2, V3, or V4.

Depending on how the Solidity token contract is written, Block 0 is triggered by one of three developer transactions:

addLiquidityETH / mint: The token has no trading switch, so the moment the deployer adds ETH + token liquidity to the Uniswap router, swaps become valid.
enableTrading() / openTrading(): Liquidity was already added in an earlier block while transfers were restricted to owner, and the deployer now broadcasts a transaction flipping tradingOpen = true.
Combined deploy + LP + enable script: A factory or router contract deploys the ERC-20, seeds the Uniswap pool, and enables trading inside a single transaction.

A block 0 sniper monitors the mempool for all three transaction signatures. The instant it sees the deployer's signed raw transaction (0x02...), it constructs a Flashbots bundle containing the deployer's raw transaction as element 0 and the sniper's swap + builder bribe as element 1.

Step-by-step: How a block 0 sniper lands a same-block buy

Step	Millisecond Timeline	Technical Action	Why It Matters
1. Mempool Detection	`0 – 30 ms`	Local Reth/Geth node streams pending tx via IPC websocket	Public RPCs add 150–400ms of lag, missing early builder cutoffs.
2. Calldata / Trace Decoding	`30 – 45 ms`	Decode `addLiquidityETH` or trace internal calls (`debug_traceCall`) to spot `tradingOpen = true`	Catches custom function names like `launch()` or `goLive()` that don't match standard ABI selectors.
3. State Simulation (`eth_callBundle`)	`45 – 80 ms`	Simulate `[dev_tx, buy_tx, test_sell_tx]` on the pending block state	Verifies exact token output, buy/sell tax %, and ensures the token isn't an instant honeypot.
4. Multi-Builder Dispatch	`80 – 150 ms`	Send `eth_sendBundle` to Flashbots, Titan, Beaverbuild, and Rsync	Covers >92% of Ethereum MEV-Boost block production.
5. Block Inclusion	`Next slot (12s)`	Block builder orders bundles by effective `block.coinbase` tip	Highest-paying non-conflicting bundles execute immediately after `dev_tx`.

You can see working TypeScript and Solidity code for this exact pipeline in our ethereum-sniper-bot-flashbots GitHub repository and our guide on How Ethereum Sniper Bots Work: Same-Block Buys With Flashbots and the Real Risks.

How Ethereum block builders order competing Block 0 snipers

On a hyped Ethereum launch, 20 to 100 different auto snipe crypto bots may spot the same openTrading() transaction in the mempool and submit a Block 0 bundle [dev_tx, sniper_i_tx] to Titan Builder and Flashbots.

Wait—if 50 bots all include dev_tx as the first transaction in their bundle, doesn't dev_tx revert 49 times?

Here is how modern Ethereum block builders (Titan, Beaverbuild, Flashbots mev-boost-relay) handle bundle merging on Block 0:

The builder recognizes that all 50 bundles share the identical first transaction hash (dev_tx).
The builder places dev_tx once, and then sorts the 50 sniper transactions (sniper_1, sniper_2, ...) in descending order of effective builder profit per gas (priorityFee + block.coinbase bribe).
As the builder packs each sniper buy into the block sequentially, the Uniswap pool price moves up along the $x \cdot y = k$ curve.
Any sniper bundle whose amountOutMin slippage limit is breached (or whose custom executor reverts because block.coinbase bribe is only paid if tokensReceived >= minTokens) is automatically dropped by the builder without landing on-chain and without costing failed gas.

We explain bundle rejection and merging rules in detail in Flashbots Bundles Explained: How to Send eth_sendBundle and Why Yours Isn't Landing.

The #1 trap for a block 0 sniper: Deadblocks and Block-0 tax modifiers

Not every token launch wants you to buy in Block 0. Many Solidity token deployers write explicit anti-sniper traps into their _update or _transfer function specifically to punish any block 0 sniper:

// Classic Solidity Block-0 trap inside _transfer():
if (block.number <= launchBlock + deadBlocks) {
    isBlacklisted[to] = true; // Or: taxRate = 99%;
}

If a contract has deadBlocks = 2 or a 99% Block-0 buy tax:

A naive bot that only checks whether buy_tx succeeds will happily buy in Block 0—and either get permanently blacklisted (isBlacklisted[to] = true) or lose 99% of its tokens to the tax wallet.
A properly engineered sniper—like the MEV DAO Ethereum Sniper Bot—always simulates a 3-step bundle ([dev_tx, buy_tx, sell_tx_in_next_block]) and checks the net ETH returned. If Block 0 triggers a blacklist or confiscatory tax, our bot automatically shifts your execution to launchBlock + deadBlocks + 1 (the first clean block).

Read our full breakdown of these contract mechanisms in Anti-Snipe Token Launches: Taxes, Blacklists, and Trading Delays and Honeypot Tokens: How to Spot One Before You Buy.

What happens when the developer launches privately (Private Block 0)?

Roughly 30%–40% of Ethereum token deployers now send their openTrading() transaction through Flashbots Protect or Titan Private RPC so it never touches the public mempool.

When a launch is private:

No public mempool Block 0 snipe is possible unless the deployer included their own wallets inside their private launch bundle.
Instead, the fastest bots run a Block 1 backrun sniper: the instant the block header/payload for Block 0 arrives from the beacon node, the bot simulates the new pool state and submits a bundle targeting Block 1 (launchBlock + 1).

Inside our MEV DAO Premium Sniping Group on Telegram, we alert members ahead of time whether a contract has deadBlocks, max-wallet limits, or private deployer patterns so your bot settings match the exact launch mechanics.

Frequently asked questions

What is a block 0 sniper in crypto?

A block 0 sniper is an automated trading bot that detects a developer's pending liquidity or trading-enable transaction in the mempool and bundles its buy order into the exact same Ethereum block (Block 0) using MEV-Boost relays like Flashbots, Titan, and Beaverbuild.

Why didn't my block 0 snipe land even though I set high gas?

On Ethereum, standard gas settings (maxFeePerGas) in MetaMask do not bundle your transaction behind a pending mempool transaction. Furthermore, if the developer sent their openTrading() transaction via a private RPC (like Flashbots Protect), it never appeared in the public mempool, meaning external bots can only buy in Block 1 (launchBlock + 1).

How do I avoid getting blacklisted when block 0 sniping?

Always use a sniper bot that simulates both the buy and a follow-up transfer/sell across launchBlock and launchBlock + 1, and inspects the contract's deadBlocks or launchBlock variables before firing. If the contract blacklists buyers in Block 0, configure your bot to target the first block after the deadblock window expires.

How much builder bribe does it take to win Block 0 on Ethereum?

Builder bribes depend entirely on how many competing snipers target the launch and the maxWallet cap of the token. Quiet launches can be won with a 0.01–0.03 ETH block.coinbase tip, while high-hype launches with 1%–2% max-wallet slots often see top-of-block bribes between 0.10 ETH and 0.50+ ETH.

Do I pay gas if my Block 0 Flashbots bundle doesn't win?

No. When your block 0 sniper submits via eth_sendBundle with a conditional builder payment and minimum token output check, any bundle that gets outbid or reverts is dropped by the block builder before inclusion, costing you 0 ETH in gas.

Related guides

Want to execute real Block 0 Flashbots snipes on Ethereum with built-in deadblock detection and 0% per-trade volume fees? Start your 3-day free trial at mevdao.org/subscribe, or message me on Telegram (@merunas).