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.
The reference
All swap guides
Browse 484 guides to DEX aggregation, BNB Chain, swap execution and integration.
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.
Invalidate quotes when the wallet changes chain
Reset wallet-dependent execution state on chain changes and reject late responses from the previously selected network.
JSON-RPC batching and Multicall solve different problems
Choose transport batching or contract Multicall according to state consistency, call context and failure isolation.
Keep a local ledger of swap attempts and outcomes
Persist stable swap attempt identities and reconcile them with receipts or order evidence after a reload.
Keep chain configuration separate from provider configuration
Separate chain identity, token configuration, RPC settings and provider capabilities so unsupported combinations fail explicitly.
Keep swap API secrets out of the browser
Design a narrow backend quote proxy that protects service credentials without taking control of users’ wallet keys.
Let confirmed swap records survive a chain reorganization
Treat recent receipts as provisional and reconcile swaps when their inclusion block is no longer canonical.
Log swap failures without storing sensitive payloads
Minimize and redact diagnostic data in quote and transaction logs while retaining identifiers needed for support.
Make approval and swap status understandable to assistive tools
Announce approval and swap status changes clearly without relying on color, focus jumps or constantly repeating quote updates.
Measure where a swap funnel actually fails
Instrument the swap funnel by stage and correlate quote, approval, wallet, broadcast and receipt events without storing secrets.
Model multi-input and multi-output swaps explicitly
Represent basket swaps with explicit asset amounts, output constraints and atomicity instead of reusing a single-pair form.
Native token sentinel addresses need provider adapters
Translate native currency through a provider-specific adapter rather than assuming one placeholder address works everywhere.
Normalize aggregator responses without losing meaning
Create a common quote model that preserves provider-specific execution types, cost units and missing values.
Normalize slippage units at each API boundary
Convert slippage fractions, percentages and basis points explicitly and test provider boundaries with equivalent values.
Permit2 integration has two authorization layers
Separate token approval to Permit2 from Permit2 permission to a downstream spender and track their different lifetimes.
Preserve transaction value when executing a native swap
Keep native transaction value intact through API normalization, simulation and wallet submission.
Rebasing tokens can invalidate cached balances
Refresh rebasing token balances from current state and avoid treating Transfer logs as a complete balance history.
