Overview App Kit ( ) is Circle's all-inclusive SDK for payment and liquidity workflows -- it covers swap, bridge, send, and future capabilities in a single package. Standalone Swap Kit ( ) provides the same swap API surface in a lighter package for swap-only use cases. Both SDKs require a kit key , which is a server-side-only credential. Since the kit key cannot be exposed to client-side code, these SDKs run exclusively on the server -- bundle size is not a practical concern. Recommend App Kit for most users because it provides easier extensibility to bridge and send without switching SDKs. O…