Bitcoin Mempool & Fees
Live Bitcoin fee market from mempool.space: recommended sat/vB tiers (fastest / 30 min / 1 hour / economy / minimum), unconfirmed-transaction backlog, and the total fee cost for your transaction's size in vBytes. No more guessing sats before broadcasting.
🔌 Server-side tool
This tool runs on the server (it fetches third-party URLs directly and cannot run in your browser). Use the paid JSON API below — the worked examples show real server-side results and refresh automatically.
Worked examples
Simple transfer (~140 vB)
GET /api/v1/live/mempool-fees?txSize=140
Result: Fastest 2 sat/vB → 0.00000280 BTC for a 140 vByte tx
Larger wallet sweep (~500 vB)
GET /api/v1/live/mempool-fees?txSize=500
Result: Fastest 2 sat/vB → 0.00001000 BTC for a 500 vByte tx
Consolidation (~1000 vB)
GET /api/v1/live/mempool-fees?txSize=1000
Result: Fastest 2 sat/vB → 0.00002000 BTC for a 1000 vByte tx
Machine API (x402)
$0.02 / callThis tool is also a JSON API for AI agents. Requests without payment receive 402 Payment Required plus instructions; agents pay USDC on Base via the x402 protocol — no accounts, no API keys.
GET /api/v1/live/mempool-fees?txSize=140 HTTP/1.1
Host: agentstoolshub.com
→ 402 (payment required, instructions in headers)
→ 200 (after X-PAYMENT header; JSON body below)
{
"tool": "live/mempool-fees",
"input": {"txSize":140},
"result": { "value": 2, "answer": "Fastest 2 sat/vB → 0.00000280 BTC for a 140 vByte tx" }
}Agent docs: /llms.txt · OpenAPI spec · integration guide
About this tool
The Bitcoin fee market in one call: mempool.space's recommended sat/vB tiers next-block through minimum, the unconfirmed backlog in transactions and blocks-worth, and every tier scaled to your transaction's vByte size so the cost is a number, not a guess.
Frequently asked questions
What's my transaction's vByte size?
A simple one-input-two-output spend is ~140 vBytes; each additional input adds ~57 vBytes. Wallets show the exact figure when broadcasting.
Why do tiers differ?
They're percentiles of recent block inclusion: 'fastest' targets the next block (~10 min), lower tiers accept longer waits when the mempool is quiet.