Mempool Inspector

The Mempool Inspector answers three everyday questions about pending (unconfirmed) transactions: how congested is the network right now, do I have anything stuck, and why hasn't my transaction confirmed. It works on Stacks, Bitcoin, and EVM chains, each with the same three modes.

Read-only and keyless. The Inspector only reads public mempool / RPC data — it never signs, broadcasts, or moves funds, and needs no admin or DM. Stacks (Hiro) and Bitcoin (mempool.space) are fully keyless.

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Supported Chains

Chain	Source	Notes
Stacks	Hiro API	Full mempool: stats, per-address pending txs, per-tx stuck diagnosis
Bitcoin	mempool.space	Full mempool: stats, per-address pending txs, per-tx stuck diagnosis (incl. CPFP & RBF)
EVM (Ethereum, Base, Arbitrum, Optimism, Polygon, BSC, Avalanche)	Alchemy RPC	Gas/fee snapshot, per-address pending count + nonce gap, per-tx stuck diagnosis

Solana is not covered. Solana has no mempool — transactions go straight to the block leader, so there is nothing pending to inspect.

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The Three Modes

You pick the mode by what you pass:

Mode	What you pass	What you get
Stats	(nothing)	A live congestion snapshot — how busy the network is and what fee gets you in right now
Address	an address	That address's pending (unconfirmed) transactions
Transaction	a tx_id / txid / tx hash	A "stuck" diagnosis for one transaction

On EVM you can also set chain (default ethereum; accepts base, arbitrum, optimism, polygon, bsc, avalanche, and aliases like eth / arb / op / matic / bnb / avax).

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Stats — "how congested is it right now?"

Run it with no address or transaction to get a network-wide snapshot.

• Stacks — total pending count, a breakdown by transaction type (token transfer / contract call / contract deploy), the fee percentiles in STX (p25/p50/p75/p95) needed to get in per type, and how long pending txs of each type have been waiting.

• Bitcoin — pending count, total backlog in vMB, projected blocks to clear, a congestion level, the current recommended fee rates in sat/vB (next block / 30 min / 1 hour / economy), and the fee histogram.

• EVM — current and next-block base fee, priority-fee percentiles (p10/p50/p90), suggested low / medium / high all-in gas prices in gwei, and the pending block's transaction count.

On EVM, the suggested gas price = next-block base fee + a priority-fee percentile. The pending-block tx count is the node's view of the next block, not the entire mempool — public RPCs don't expose the full pending pool.

Address — "do I have pending transactions?"

Pass an address to see what's unconfirmed for it.

• Stacks — outgoing and incoming pending txs with fee, nonce, type, and age.

• Bitcoin — pending txs touching the address, each with fee, vsize, sat/vB rate, and net value direction (incoming / outgoing).

• EVM — the count of pending transactions plus a nonce-gap read (confirmed vs pending nonce). Public RPCs don't expose the individual pending txs, so this is a count, not a listing.

Transaction — "why is my tx stuck?"

Pass a transaction id/hash for a stuck diagnosis.

• Stacks — the tx's fee vs live mempool fee percentiles for its type (underpriced / below median / competitive) and a sender nonce-gap check — the most common reason a tx won't confirm regardless of fee.

• Bitcoin — the tx's sat/vB rate, the effective rate including any CPFP child, a verdict vs current recommended tiers (competitive / low / underpriced), and whether RBF is signaled (so you know if you can bump it).

• EVM — whether the tx is still pending, its max/effective gas price vs the current base fee and median priority, and a sender nonce-gap check (is it stuck behind an earlier-nonce tx?).

A nonce gap means an earlier transaction from the same sender hasn't confirmed yet — everything behind it is blocked regardless of fee until that one confirms or is replaced. The Inspector flags this on Stacks and EVM.

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Example Prompts

"How congested is the Bitcoin mempool right now, and what sat/vB do I need for the next block?"

"What gas price do I need on Base at the moment?"

"Why is my Stacks transaction stuck? 0x…"

"Do I have any pending transactions? SP…"

"Is this Bitcoin tx going to confirm or is the fee too low? <txid>"

"Check this Ethereum tx — is it stuck behind an earlier nonce? 0x…"

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Using It From an Agent (x402 / MCP)

The per-chain tools are on the public Tools Platform as stacks-mempool-inspector, bitcoin-mempool-inspector, and evm-mempool-inspector (REST + MCP, free). Agents can use them to time a broadcast (wait for low fees), right-size a fee before signing, or detect and recover a stuck transaction (bump via RBF/CPFP on Bitcoin, or replace-by-nonce on Stacks/EVM) in autonomous on-chain workflows.

Type /cancel anytime to stop a multi-step flow.