Mempool vs MercadoBitcoin

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.

Mercado Bitcoin is Brazil's oldest and largest cryptocurrency exchange, operating since 2013 with spot trading across dozens of BRL pairs. Its v4 REST API and companion WebSocket service expose public market data — candles, order books, tickers — without authentication, while trading and account endpoints require an API key created from account settings. The API is free to use for individual developers.