Ethereum mempool explorer: see what’s pending

An Ethereum mempool explorer shows you the waiting room of the network: transactions that have been signed and broadcast but are not yet in a block. Most of the time you never notice it, because a transaction with a sensible fee waits a single 12-second slot. You notice it when something goes wrong. A swap sits at “pending” for forty minutes. You send three transfers in a row and the last two refuse to move while the first one hangs. A trade fills at a noticeably worse price than the quote. All three stories start in the mempool.

This guide explains what the mempool really is after the Merge, which mempool explorer tools still work in September 2026 (several popular ones have shut down), how to unstick a transaction by reusing its nonce, and how sandwich bots use the public mempool against ordinary traders.

What the Ethereum mempool is (and why there isn’t just one)

“The mempool” sounds like a single global queue. It isn’t. Every execution client, whether Geth, Nethermind, Besu, Erigon or Reth, keeps its own transaction pool in memory. When you press Send, your wallet hands the signed transaction to one RPC node. That node checks the signature, the nonce and the balance, then gossips the transaction to its peers, who gossip it onward. Within a second or two most well-connected nodes have a copy, but not all of them, and not in the same order.

Each pool also has limits. Geth’s defaults, for instance, cap the number of slots per account and across the whole pool, and they evict the cheapest transactions first when memory fills up. Transactions are sorted into two buckets. Pending (executable) ones have the next expected nonce and enough balance, so a block builder could include them right now. Queued ones are waiting on something, usually an earlier nonce that has not arrived. Every mempool explorer you use shows one node’s, or one provider’s, snapshot of those buckets. Two explorers disagreeing about how many transactions are pending is normal, not a bug.

Since the Merge in September 2022, blocks are proposed by validators on the beacon chain rather than by miners, one per 12-second slot. That changed who picks transactions from the mempool, which is the next part of the story. If you want the validator side of it, our beacon chain explorer guide covers slots, proposers and epochs.

Private orderflow, MEV-Boost and block builders

In theory the validator whose turn it is builds the block. In practice, the large majority of validators run MEV-Boost, software that lets them outsource block construction. Specialised builders assemble the most profitable block they can and bid for the slot through relays. Public relay dashboards have shown roughly nine in ten mainnet blocks arriving this way for a long time. The validator simply signs the highest bid.

Builders do not only read the public mempool. They also receive private orderflow: transactions sent straight to them by wallets, trading bots, DEX aggregators and privacy RPCs such as Flashbots Protect or MEV Blocker. Those transactions are never gossiped, so no mempool explorer can see them before they land. When you open a fresh block and find a transaction that “skipped” the mempool entirely, this is why. It is also why pending-transaction counts understate real demand, and why a gas estimate built purely from the public pool can be off.

The next protocol upgrade, Glamsterdam, is set to bring enshrined proposer-builder separation (EIP-7732) into the protocol itself. It was still in testing as of September 2026, so treat any activation date you see quoted with care.

Mempool explorer tools that still work in 2026

We checked the usual suspects in September 2026. Here is what is alive and what each one is good for.

Etherscan pending transactions

The Etherscan pending transactions page lists what Etherscan’s own nodes currently hold, with the sender, nonce, gas price and how long each transaction has been waiting. You can filter by address, which is the quickest way to see whether your own transaction is still in their pool. A related pending transactions chart tracks the pool size over time, handy for spotting congestion. For a full tour of the rest of the site, see our Etherscan review.

Blockchair mempool view

Blockchair’s Ethereum mempool page treats pending transactions like a database table: sort by value, gas price or time seen, and filter with the same SQL-style controls the rest of the explorer uses. It is the better choice when you want to answer a question such as “how many pending transfers above 100 ETH are there right now?”. We look at its strengths and privacy stance in the Blockchair review.

txstreet visualiser

txstreet is the fun one. Each pending transaction becomes a little person waiting for a bus, and each block is a bus leaving the station. It won’t help you debug a nonce, but it makes congestion obvious in a way numbers don’t, and it is a great way to explain the mempool to someone new. It was still online when we checked.

Your own node

The most honest mempool explorer is your own node. Any execution client exposes pending transactions over JSON-RPC: eth_subscribe with newPendingTransactions streams hashes as they arrive, and Geth’s txpool_content dumps the whole pool, pending and queued. Pair that with a local explorer from our open-source explorer guide and you see exactly what your node sees, with no third party logging your interest. If you would rather use a hosted service, our Ethereum explorer API comparison covers providers with pending-transaction endpoints.

What happened to the Blocknative mempool explorer

For years, the phrase “Blocknative mempool explorer Ethereum” meant one thing: a real-time dashboard that watched the mempool from many nodes around the world. In December 2023 Blocknative relaunched it as Ethernow (ethernow.xyz), pitched as an explorer for pre-chain data. You could watch a transaction enter the pool, see which builders included it, and compare what was pending against what ended up in the block.

That era is over. Blocknative sunset Ethernow and its mempool archive service, with support ending on 1 March 2025, to focus on its Gas Network project (it said the historical archive data would stay accessible through its documentation). Then, in its sunset notice, the company said its API services, including the mempool and gas APIs and Gas Network, would run only through 19 June 2026, after which they would stop responding. The same notice says the team was joining Deloitte. When we tried ethernow.xyz in September 2026, it no longer loaded.

If you maintain a bot, a wallet or a dashboard that still calls Blocknative, it is broken now, not later. The practical replacements are a node subscription as described above, a commercial RPC provider with pending-transaction streams, or a gas oracle based on recent blocks rather than the pool. For fee estimates in particular, our Ethereum gas tracker reads the live base fee and priority fees directly from the chain.

Why Ethereum transactions get stuck in pending

Almost every stuck transaction comes down to one of two causes: a fee that is too low, or a nonce gap.

A fee below the base fee. Since EIP-1559, every block has a base fee that must be paid and is burnt. Your transaction sets a maxFeePerGas. If the base fee rises above that ceiling, say you signed with a max of 1.2 gwei and a busy NFT mint pushes the base fee to 4 gwei, your transaction is simply not eligible. It waits until the base fee falls back or you replace it. In calm 2026 conditions, with average gas well under a few gwei, this happens far less often than it did in 2021, but spikes still occur.

A nonce gap. Every account has a counter, the nonce, and transactions must be mined strictly in order. Suppose your wallet has sent 41 transactions (nonces 0 to 40). You now send nonce 41 with a low fee, then get impatient and send nonces 42 and 43 with generous fees. Nonces 42 and 43 cannot go first. They sit in the queued bucket, and your wallet shows three pending transactions even though only one is actually the problem. Nonce gaps also appear when you use the same key in two wallets, or when a wallet’s custom nonce setting skips a number.

How to unstick an Ethereum transaction (replace-by-fee)

Ethereum has no “cancel” message. What it has is a simple rule: only one transaction per account per nonce can ever be included. So you fix a stuck transaction by sending a new one with the same nonce and a higher fee. Nodes and builders prefer the better-paying version, and once it is mined the original becomes permanently invalid. Wallets call this Speed up or Cancel. Developers call it replace-by-fee.

1. 1

   Find the stuck transaction and its nonce

   Open the hash in an explorer (our live explorer or Etherscan) and note the nonce and the max fee. Then open your address and check whether any earlier nonce is still missing: if nonce 41 never landed, 42 and 43 will wait forever.

2. 2

   Compare your fee with the current base fee

   Look up the base fee on a gas tracker. If your maxFeePerGas is below today’s base fee, no block can include the transaction until the network calms down. That is the classic stuck-in-pending case.

3. 3

   Decide: speed up or cancel

   Speed up re-sends the same action with higher fees. Cancel sends 0 ETH to yourself with the same nonce, so the original action never happens. Both are just a new transaction that reuses the old nonce.

4. 4

   Send the replacement with the same nonce and higher fees

   Use the wallet’s Speed up / Cancel button, or enable custom nonce and send manually. Raise both the max fee and the priority fee by at least 10% (Geth’s default rule; blob transactions need 100%). A smaller bump is usually rejected as “replacement transaction underpriced”.

5. 5

   Fill any nonce gap

   If an earlier nonce is missing, send a small transaction (for example 0 ETH to yourself) with exactly that nonce and a healthy fee. Once it confirms, the queued transactions behind it become executable and usually clear within a block or two.

6. 6

   Confirm the result in the explorer

   Refresh the original hash. It should show as dropped or replaced, and the new hash appears on your address with the same nonce. Only one transaction per nonce can ever be mined, so this is your proof that the old one is dead.

One caution about the “replacement transaction underpriced” error: it means the node you are talking to still holds the old version and your new fees are not at least 10% higher on both maxFeePerGas and maxPriorityFeePerGas. Bump both fields, not just one. And if the explorer suddenly shows the original as mined while you were preparing the replacement, stop. The nonce is used, and the replacement will now fail with “nonce too low”, which is harmless.

MEV sandwich attacks, explained simply

MEV, maximal extractable value, is the profit someone can make by choosing the order of transactions in a block. Some MEV is harmless or even useful, such as arbitrage that keeps DEX prices in line. The kind that hurts ordinary users is the sandwich attack, and it lives entirely off the public mempool.

Picture it with round numbers. You submit a Uniswap swap of 10 ETH for USDC with a 1% slippage tolerance. That tolerance is visible in the pending transaction: it literally says “I will accept anything down to this minimum amount of USDC”. A bot watching the mempool spots it and builds a three-transaction bundle. First, the bot buys USDC with ETH just before you, pushing the price up. Second, your swap executes at the worse price, still within your 1% limit, so it succeeds. Third, the bot sells back straight after you and pockets the difference. You lose close to your full slippage allowance; the bot keeps most of it and pays part to the builder to guarantee the ordering.

You can spot a sandwich after the fact in any explorer: open the block, find your swap, and look at the transactions directly before and after it in the same pool from the same address or contract. Our smart contract explorer guide shows how to read decoded swap logs, which makes the pattern easy to see.

How to protect your swaps from the public mempool

The cleanest defence is to not broadcast publicly in the first place. A private RPC sends your transaction straight to builders instead of gossiping it. Flashbots Protect (https://rpc.flashbots.net) and MEV Blocker are the best-known options; both can be added to MetaMask or any wallet as a custom network RPC for Ethereum mainnet. Flashbots Protect also does not charge you for transactions that would revert, and both services can return some of the backrun value to you. Many wallets and DEX aggregators now route swaps privately by default, so check your wallet’s settings before adding anything.

Next, keep slippage tight. A 0.3–0.5% tolerance on a liquid pair gives a sandwich bot very little room, while the 3% or “auto” settings some interfaces default to invite trouble. For large trades, split the order or use a venue that settles through batch auctions or solvers, where your order is not exposed to the public pool the same way.

Finally, learn to check your own history. After a swap, paste the hash into our live Ethereum explorer and compare what you received with the quote. If the gap keeps landing near your slippage limit, something is eating your trades, and moving to a private RPC is worth the two minutes it takes. Our address explorer guide shows how to review a whole wallet’s activity in one pass, and the beginner’s guide to using an Ethereum explorer covers the basics if any of these screens are new to you.