Mempool vs Solana JSON RPC

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.

Solana's public JSON-RPC clusters expose the full read/write RPC surface — accounts, transactions, blocks, and WebSocket subscriptions — with no signup or API key required. They're free to call, but Solana's own docs are explicit that the shared public endpoints are rate-limited to roughly 100 requests per 10 seconds per IP and are not intended for production traffic, pointing serious usage toward a dedicated third-party RPC provider instead.