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 19 Aug 2026

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 19 Aug 2026, 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

Parameter	Type	Required	Description
`v1/fees/recommended`	path	Optional	Recommended fee rates by confirmation target. `v1/fees/recommended`
`blocks`	path	Optional	Recent blocks. `blocks`
`tx/<txid>`	path	Optional	Transaction details. `tx/abc123`
`address/<address>`	path	Optional	Address 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.

Alternatives to mempool.space API

If mempool.space does not fit, these finance & crypto apis cover similar ground. Every one was called before publishing, and each links to its own reference page with a working curl command and the response it returned.

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All Finance & Crypto APIs

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