White-label crypto swap: what you still need to build
Compare a swap widget, SDK and direct API integration, including ownership of wallet state, fee disclosure, support and operational controls.
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Integration engineering
Handle precision, validation, reliability and the operating details behind a swap interface.
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A broadcast timeout does not prove a swap failed
Preserve unknown transaction outcomes after broadcast timeouts and reconcile before constructing another swap.
A gas estimate failure may be a contract revert
Distinguish contract reverts from insufficient gas when a swap transaction cannot be estimated.
A transaction hash is not a successful swap
Use receipt status and actual output evidence to distinguish submitted, mined, successful and economically reconciled swaps.
Account for partial fills without double counting
Deduplicate intent fill events and keep settled amounts, remaining quantity and terminal status independently reconcilable.
Avoid nonce collisions across concurrent swap actions
Coordinate account nonces for approval and swap transactions, including concurrent workers and external wallet activity.
Build a Max button that leaves gas available
Calculate a native-asset Max amount with a fee reserve and revalidate it when the route or gas estimate changes.
Build an order state machine for intent-based swaps
Track intent submission, acceptance and settlement as separate states with distinct order and transaction identities.
Build swap fixtures that test failures as well as happy paths
Build a compact fixture matrix around dangerous state transitions, provider responses and numerical edge cases.
Cancellation requests need their own confirmation state
Represent cancellation as a requested action until the provider or chain confirms that the unfilled order can no longer execute.
Check the RPC chain before reading balances or sending
Verify each RPC endpoint’s chain identity before using its balances, allowances, simulations or transaction submission.
Compare quotes after separating output and network cost
Compare net quote economics by identifying included fees, separate gas costs and uncertainty in token-to-USD conversions.
Convert swap amounts without floating-point errors
Parse decimal token inputs into exact base-unit integers and preserve them through JSON and wallet serialization.
Define the trust boundary around an embedded swap widget
Specify origin checks, wallet authority and verified settlement events at the boundary between a swap widget and its host.
Detect API schema drift before it reaches wallet prompts
Monitor provider response contracts with semantic assertions and safe preview requests, while avoiding unintended firm-order traffic.
Handle dust and rounding at the transaction boundary
Apply explicit integer rounding policies to tiny swap amounts, minimum outputs and display values.
Handle HTTP 429 without creating a retry storm
Apply bounded retries and shared backpressure to throttled quote requests, respecting Retry-After without assuming fixed quotas.
Handle nonstandard token return values in swap adapters
Handle ERC-20 false returns and missing return data according to compatible contract wrappers rather than assuming every token behaves identically.
Handle tokens that require allowance to be reset
Implement a receipt-aware zero-first allowance sequence for tokens that reject replacing one nonzero approval with another.
Invalidate approvals and quotes after an account switch
Bind quote, allowance and signature state to the connected account and protect it from late results after a wallet switch.