Blockchain.com vs Mempool

Blockchain.com's free Explorer API returns JSON data for Bitcoin blocks, transactions, and addresses with no signup or key, alongside a Statistics/Charts API, an Exchange Rates API, and a WebSocket feed for real-time block and mempool notifications. Browser callers can opt individual GET requests into CORS by appending a cors=true parameter; this read-only data API is a separate product from Blockchain.com's API-key-gated Exchange trading API.

mempool.space runs an open-source Bitcoin block explorer and fee-estimation API — originally forked from Blockstream's Esplora backend and now maintained as its own mempool/electrs fork — answering over REST and WebSocket with no signup needed to read blocks, transactions, addresses, and the Lightning Network graph. It's free for public use, with a paid Mempool Enterprise tier adding unmetered access and multi-datacenter SLAs for heavier commercial traffic.