# EsploraBlockSource A [`BlockSource`](/documentation/BitcoinKernel/BlockSource) backed by any Esplora-compatible HTTP endpoint — mempool.space, blockstream.info, or a self-hosted Esplora instance. ``` struct EsploraBlockSource ``` ## Overview> Important: No endpoint is hard-coded as a default. Callers MUST provide > one. The library ships convenience accessors for known public instances > (see `URL.mempoolSpaceSignet` et al.), but the choice of which network > to trust is an explicit caller decision — ``doc://BitcoinKernel/documentation/BitcoinKernel`` does not > silently pick a block explorer on behalf of the user. ### Pacing, retry, and rate-limiting - A per-instance `RequestPacer` actor ensures sequential requests stay at least `minimumInterRequestDelay` apart (default: 100 ms). - Failures with HTTP 5xx or 429 are retried up to `maximumRetries` times with exponential backoff (base = `baseRetryDelay`, doubling each time, capped at 2^6 × base). - When the server sends a `Retry-After` header on a 429 or 5xx response, the client honors it in preference to the exponential-backoff delay. - Transient network errors (timeouts, DNS failures, connection drops) are retried on the same policy. - Other non-2xx responses (e.g., 400, 403) fail immediately with ``doc://BitcoinKernel/documentation/BitcoinKernel/BlockSourceError/invalidResponse(_:)``. - 404 maps immediately to ``doc://BitcoinKernel/documentation/BitcoinKernel/BlockSourceError/notFound`` without retry. ### Hash orientation `Data` hashes on this type are in internal (kernel) byte order, matching the [`BlockSource`](/documentation/BitcoinKernel/BlockSource) contract. Translation to Esplora’s display-hex format happens inside the implementation at the HTTP boundary.