dYdX vs Mempool

dYdX is a decentralized perpetuals exchange that migrated from its StarkEx-based v3 to a Cosmos-chain v4 architecture, replacing the old exchange API with an open-source Indexer exposing markets, orderbooks, trades, and candles over REST and WebSocket. Anyone can run their own Indexer instance, but the public one at indexer.dydx.trade needs no signup for market-data reads — it's rate-limited rather than API-key gated.

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.