Gemini vs Mempool

Gemini's REST and WebSocket APIs cover public market data (tickers, order books, trade history) alongside authenticated endpoints for order placement, account status, and FIX Drop Copy. Public market-data calls need no credentials, while trading and account endpoints require an HMAC-signed API key/secret pair with role-based permissions such as separate Trader and Fund Manager roles.

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.