Blockchain.com vs dYdX

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.

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.