How to Read the Mempool: A Beginner's Field Guide for 2026

Answer first — Reading the mempool is pattern-matching for transactions that haven't been included yet. In 2026 the public mempool on Ethereum is mostly dominated by spam and decoys, but on most L2s it's still a usable signal source. The five patterns worth learning to recognize on sight are: large swaps, multi-hop router calls, oracle-update bundles, liquidation-trigger setups, and unbalanced mints. Once you see them, MEV opportunities are obvious. Until then, mempool data is just noise.

If you haven't read What is MEV, start there.

What the Mempool Actually Is

A pool of unconfirmed, signed transactions broadcast by users to the network, waiting for inclusion in a block. Each transaction has:

• from, to, value
• data (calldata — the encoded function call and args)
• gasLimit, gasPrice / maxFeePerGas
• nonce

In 2026, "the mempool" is plural:

• Public mempool (Geth, Reth, Erigon, Nethermind defaults) — anyone can subscribe via eth_subscribe('newPendingTransactions').
• Private mempools — Flashbots Protect, MEV-Share, builder-only pools. Not visible to public WSS.
• Sequencer queues (L2s) — varies; some publish, some don't.

Most retail searchers are reading the public mempool. Most institutional flow has migrated to private. That asymmetry shapes what you'll see.

Setting Up a Read-Only Mempool Stream

Minimum viable setup:

1. A WSS endpoint with pendingTransactions subscription. See Best WSS Endpoints by Chain.
2. A decoder. Either ethers.js with ABI lookups, or a hosted decoder like Blocknative.
3. A filter — most pending txs are noise.

Subscription example (ethers v6):

js

const ws = new WebSocketProvider(WSS_URL);
ws.on('pending', async (txHash) => {
  const tx = await ws.getTransaction(txHash);
  if (!tx) return;
  // filter and decode here
});
Copy

Expect 50–500 pending tx/sec on Ethereum mainnet at peak. Streaming is fine; storing all of them is not.

The Five Patterns Worth Learning

1. Large Swaps (the simplest signal)

A pending Uniswap router call with a value in the millions of dollars equivalent is the canonical MEV target. Read the calldata to extract:

• Input token + amount in
• Output token + amount out (minimum)
• Slippage tolerance

If slippage > 1% on a multi-million swap, there's typically a backrun-able imbalance. See Backrun vs Sandwich Strategy.

2. Multi-Hop Router Calls

Swaps routed across 3+ pools usually create transient imbalances at intermediate pools. Decode the path; check the middle pools for arb opportunities post-execution.

3. Oracle-Update Bundles

Chainlink price-update transactions arrive in clusters before liquidations. If you see oracle update + immediate Aave/Morpho call on the same block, a liquidation is being opened. Knowing oracle update timing is half the liquidation strategy.

4. Liquidation-Trigger Setups

Specific calldata patterns to liquidation-eligible positions. On Aave v3, look for liquidationCall(...) selector 0x00a718a9. Tracking the position health factor off-chain is what tells you which positions are about to flip.

5. Unbalanced Mints / Burns

Liquidity-add transactions where the ratio is off-market signal a price gap forming. Pre-position on the side that's about to be cheap.

What's Noise

The mempool is mostly noise:

• Failing-tx spam (nonce conflicts, insufficient balance) — ignore
• Approval transactions (approve()) — not directly useful
• Self-transfers between own wallets — ignore
• ERC-20 transfers under $1k — usually irrelevant
• Replay-protected duplicates — count once

Filter aggressively. A good filter cuts the firehose to ~5% of input.

Why the Mempool Is Less Useful in 2026

Three structural shifts since 2023:

1. Private order flow. Most large retail swaps now route through Flashbots Protect or MEV-Share by default in major wallets (MetaMask, Rabby). They never hit the public mempool.
2. Stealth mempool spam. Sophisticated actors broadcast decoy transactions to mislead naive searchers. Acting on every "big swap" without simulation gets you sandwiched yourself.
3. L2 sequencer asymmetry. On Base/Arbitrum, the sequencer sees the queue first. By the time a tx hits a public WSS, the sequencer has already ordered it.

So the public mempool is a secondary signal source in 2026. Primary signal is:

• Direct sequencer WSS where available
• Builder/relay private streams (paid)
• On-chain state (every block)

Reading Calldata: The Skill That Compounds

Every meaningful mempool tx has calldata. Learn to read it. Tools that decode automatically:

• ethers.Interface with the right ABI
• Etherscan decode endpoint
• Tenderly transaction inspector
• Foundry's cast 4byte-decode

Manually:

0x38ed1739 — swapExactTokensForTokens
0x18cbafe5 — swapExactTokensForETH
0x7ff36ab5 — swapExactETHForTokens
0xb6f9de95 — swapExactETHForTokensSupportingFeeOnTransferTokens
0x00a718a9 — liquidationCall (Aave v3)
0x52aaef71 — liquidate (Compound)
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Memorize the top 10 selectors for whatever chains you operate on.

Building a Mental Filter

After 2–3 weeks of watching, you'll start subconsciously noticing patterns:

• "That's a big USDC→WETH on Uniswap V3 fee 5bps"
• "That nonce gap means there's a previous tx pending"
• "That gas tip is 3x median — they want fast inclusion"

This intuition is what separates effective searchers from people running off-the-shelf bots. FRB Agent automates the execution but still benefits enormously from operators who can read the stream when something weird happens.

Recommended Daily Practice

For the first 4 weeks of MEV operation:

1. Watch a filtered mempool stream 30 min/day.
2. Pick 3 large pending swaps; predict outcome before block confirms.
3. Compare to actual block.
4. Track your prediction accuracy.

You'll be a useful operator after about 80 hours of practice. There's no shortcut.

Mempool on Solana

Solana doesn't have a traditional mempool — transactions go directly to the leader. The closest equivalent is monitoring:

• Validator queues (via Jito API)
• Pre-leader transmission via gulf-stream (limited public visibility)
• Block-by-block state changes (post-hoc but fast)

For Solana flow see Solana MEV vs Ethereum MEV.

FAQ

Can I make money from just watching the mempool manually?

Almost never. By the time a human sees and acts on a tx, the next block has confirmed. Mempool reading is for configuring strategies, not for execution.

Is it legal to read the mempool?

Yes. The public mempool is, by definition, public. Reading it is not different from reading public blockchain state.

Do I need a paid WSS provider?

For learning, no — public RPCs work. For production, yes — public providers throttle pendingTransactions subscriptions aggressively.

Will the mempool disappear with private order flow?

On L1, possibly. Public mempool volume has fallen 40%+ since 2022. On L2s, usage patterns differ; some L2s never had a public mempool.

Does FRB Agent show the mempool to me?

Yes, in the dashboard's "Mempool Tape" view. Filtered to relevant transactions for your enabled strategies.

Related Reading

• Mempool Scanning Filters & Latency
• Private Bundle vs Public Mempool
• Best WSS Endpoints by Chain
• What is MEV — Practical Guide
• Flashbots Bundles Explained

This article is educational. Mempool reading is a skill that takes weeks of practice. Not financial advice.