BYTETOOLS

mempool.space API

Free Bitcoin blockchain API with no key: recommended transaction fees, mempool state, blocks, transactions and address data. Self-hostable. Tested example.

No API key requiredCORS enabledHTTPSFree tier

Endpoint tested and returned HTTP 200 on 2026-08-19

What is the mempool.space API?

mempool.space is a free, key-free Bitcoin blockchain explorer API providing recommended transaction fee rates, live mempool state, block and transaction data, and address balances.

The fee recommendation endpoint is the one most applications need. It returns suggested satoshi-per-vbyte rates for several confirmation targets, which is exactly what a wallet needs to set a sensible fee without over- or underpaying.

The whole stack is open source and self-hostable, which matters for a financial application — you can run your own instance against your own Bitcoin node rather than trusting a third party for fee estimation.

Quick facts

Base URL
https://mempool.space/api
Authentication
No API key required for the public instance.
Rate limit
Public instance limits are not formally published; heavy users should self-host.
Pricing
Free and open source.
CORS
Enabled — callable directly from browser JavaScript
Official docs
Read the docs

How to use the mempool.space API

Every request below was executed against the live API on 2026-08-19, and the response shown is the real body it returned — not an illustration.

1. Get recommended Bitcoin transaction fees

GET https://mempool.space/api/v1/fees/recommended

curl
curl 'https://mempool.space/api/v1/fees/recommended'
JavaScript (fetch)
const res = await fetch("https://mempool.space/api/v1/fees/recommended");
if (!res.ok) throw new Error(`Request failed: ${res.status}`);
const data = await res.json();
console.log(data);
Python (requests)
import requests

res = requests.get("https://mempool.space/api/v1/fees/recommended", timeout=20)
res.raise_for_status()
print(res.json())
Response — HTTP 200
{
  "fastestFee": 3,
  "halfHourFee": 3,
  "hourFee": 1,
  "economyFee": 1,
  "minimumFee": 1
}

Parameters

ParameterTypeRequiredDescription
v1/fees/recommendedpathOptionalRecommended fee rates by confirmation target. v1/fees/recommended
blockspathOptionalRecent blocks. blocks
tx/<txid>pathOptionalTransaction details. tx/abc123
address/<address>pathOptionalAddress balance and transaction stats. address/bc1q...

Response fields

fastestFeeinteger
sat/vB for confirmation in the next block.
halfHourFeeinteger
sat/vB for roughly 30-minute confirmation.
hourFeeinteger
sat/vB for roughly one-hour confirmation.
economyFeeinteger
Low-priority rate.
minimumFeeinteger
Minimum relay fee currently accepted by the mempool.

What you can build with the mempool.space API

  • Set appropriate transaction fees in a Bitcoin wallet
  • Monitor mempool congestion and fee spikes
  • Build a block explorer or transaction tracker
  • Alert users when fees drop below a threshold

Common errors and how to fix them

Fees seem very high

The mempool is congested; this is real market data, not an error.

Fix: Show the user the economy option and let them wait rather than forcing the fastest rate.

404 on a transaction

The transaction is not in the mempool or chain.

Fix: Unconfirmed transactions can be dropped from the mempool; handle the not-found case.

Rate limiting on the public instance

Shared infrastructure.

Fix: Self-host mempool.space against your own node for production financial use.

mempool.space API — frequently asked questions

Is the mempool.space API free?

Yes, the public instance is free with no API key. The entire stack is open source and can be self-hosted.

What are the fee units?

Satoshis per virtual byte (sat/vB). Multiply by your transaction's virtual size to get the total fee in satoshis.

Which fee rate should a wallet use?

It depends on urgency. fastestFee targets the next block, halfHourFee and hourFee are cheaper with longer waits, and economyFee is for non-urgent transactions. Let the user choose.

Should I use the public instance in production?

For a real financial product, self-host against your own Bitcoin node. That removes both the rate limit and the trust dependency on a third party.

Tools that pair with this API

JSON Formatter

Format, beautify and minify JSON online with 2-space, 4-space or tab indentation. Sort keys alphabetically and catch syntax errors instantly — free and private.

Unit Converter

Convert between units of length, weight, temperature, area, volume, speed, time and data storage instantly, with a swap button and common conversion tables.

mempool.space is an independent third-party service and is not affiliated with ByteTools or ByteVancer. Details on this page were verified on 2026-08-19; always check the official documentation before relying on this API in production, as terms and limits can change.