Handling amount changes during swap

The API does not explicitly indicate that the amount has changed beyond an acceptable threshold. It always returns the latest calculated amount, and it is the integrator’s responsibility to detect significant changes and request user confirmation.

Key responsibility of the integrator

When performing a swap, the integrator must:

store the output amount returned by quote
compare it with the output amount returned by swap
detect significant deviations
explicitly confirm the new amount with the user
send a new swap request only after user approval

Automatic execution without user confirmation is not recommended when the amount changes significantly.

Why amount changes happen

Reason	Description
Market movement	Token prices may change between quote and swap
Liquidity updates	Available liquidity on DEXes or bridges may change
Provider recalculation	Providers may recalculate output during execution

Because of this, the amount returned by swap should always be treated as final and authoritative.

Recommended deviation threshold

Rubic recommends using a ±0.5% deviation threshold. If the new amount exceeds this range compared to the quoted amount, the integrator should pause execution and request user confirmation.

Recommended execution flow

Step	Action
1	Call quote and store toTokenAmount
2	User confirms and initiates swap
3	Call swap and receive updated toTokenAmount
4	Compare quote amount with swap amount
5	If deviation is above threshold, show confirmation UI
6	If user approves, send a new swap request
7	If user rejects, cancel execution

Amount comparison example

The following example checks whether the new amount differs from the quoted amount by more than 0.5%.

const changePercent = 0.5;
const acceptablePercent = new BigNumber(changePercent).dividedBy(100);

const oldAmount = new BigNumber(oldWeiAmount);
const newAmount = new BigNumber(newWeiAmount);

const upperBound = oldAmount.multipliedBy(acceptablePercent.plus(1));
const lowerBound = oldAmount.multipliedBy(new BigNumber(1).minus(acceptablePercent));

const isOutOfRange =
  newAmount.lt(lowerBound) || newAmount.gt(upperBound);

if (isOutOfRange) {
  throw new AmountChangeWarning(oldWeiAmount, newWeiAmount);
}

Handling amount change on the client

When an amount change is detected, the integrator should pause execution and notify the user.

Example handling logic

if (err instanceof AmountChangeWarning) {
  const rateChangeInfo = {
    oldAmount: Token.fromWei(err.oldAmount, trade.to.decimals),
    newAmount: Token.fromWei(err.newAmount, trade.to.decimals),
    tokenSymbol: trade.to.symbol
  };

  const allowSwap = await onRateChange(rateChangeInfo);

  if (allowSwap) { 
    // retry swap
  }
}

User confirmation UI

The integrator may choose any UI approach, as long as the confirmation is explicit.

Common UI patterns

confirmation modal
inline warning with accept / cancel buttons
full-screen confirmation step (mobile)

Field	Description
Previous amount	Amount from quote
New amount	Amount from swap
Token symbol	Destination token
Action	Continue / Cancel

Important notes

The API does not signal that the amount change is significant
The integrator must perform the comparison manually
Users must explicitly approve any significant change
A new swap request is required after confirmation
Silent or automatic acceptance is strongly discouraged

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Tokens API

Handling amount changes during swap

Key responsibility of the integrator

Why amount changes happen

Recommended deviation threshold

Recommended execution flow

Amount comparison example

Handling amount change on the client

Example handling logic

User confirmation UI

Common UI patterns

Recommended confirmation content

Important notes

​Key responsibility of the integrator

​Why amount changes happen

​Recommended deviation threshold

​Recommended execution flow

​Amount comparison example

​Handling amount change on the client

​Example handling logic

​User confirmation UI

​Common UI patterns

​Recommended confirmation content

​Important notes

Key responsibility of the integrator

Why amount changes happen

Recommended deviation threshold

Recommended execution flow

Amount comparison example

Handling amount change on the client

Example handling logic

User confirmation UI

Common UI patterns

Recommended confirmation content

Important notes