Swap Instruction Reference

Technical reference for the Stableswapper swap instruction. For setup and examples, see Quickstart or Examples.

Ethereum Virtual Machine
Solana Virtual Machine

Swap Function

Contract: 0x57AB1E2c6289aCe985Bd5c5571EbF6d98CD41Ab7 (Key Addresses)

Function Signature

function swap(
    address tokenIn,
    address tokenOut,
    uint256 amountIn,
    uint256 minAmountOut,
    address recipient
) external

Parameters

Parameter	Type	Description
`tokenIn`	`address`	Address of the ERC-20 token being swapped from
`tokenOut`	`address`	Address of the ERC-20 token being swapped to
`amountIn`	`uint256`	Amount of input token to swap (in token’s native decimals, before fees)
`minAmountOut`	`uint256`	Minimum acceptable output amount (slippage protection)
`recipient`	`address`	Address that receives the output tokens

Preconditions

The caller must have approved the Stableswapper contract to spend at least amountIn of tokenIn (ERC-20 approve)
Both tokenIn and tokenOut must be listed and swappable
The SWAP feature flag must be enabled
If the ALLOWLIST feature is enabled, msg.sender must be allowlisted
amountIn and minAmountOut must be greater than zero
tokenIn and tokenOut must be different addresses
recipient must not be the zero address

Fee Model

Fees are charged on the input token and deducted before the 1:1 swap calculation.

Step	Description
1	Full `amountIn` is transferred from the caller to the contract
2	Fee is calculated: `fee = ceil(amountIn * feeBasisPoints / 10000)`
3	Fee is transferred from the contract to the `feeRecipient`
4	Net amount (`amountIn - fee`) is normalized for decimal differences and sent to `recipient`

Example: Swapping 100 USDC with a 1% fee (100 basis points):

User sends: 100 USDC
Fee: 1 USDC (sent to fee recipient)
User receives: 99 of the output token (normalized for decimals)

View Functions

Token State

Function	Returns	Description
`isTokenListed(address token)`	`bool`	Whether a token is listed on the contract
`isTokenSwappable(address token)`	`bool`	Whether a listed token is currently enabled for swapping
`getTokenDecimals(address token)`	`uint8`	Cached decimals for a listed token
`getListedTokens()`	`address[]`	Array of all listed token addresses
`getListedTokensCount()`	`uint256`	Number of listed tokens
`getReservedAmount(address token)`	`uint256`	Amount reserved (not available for swaps)

Fee Configuration

Function	Returns	Description
`feeBasisPoints()`	`uint16`	Current fee in basis points (e.g., 100 = 1%)
`feeRecipient()`	`address`	Address that receives collected fees

Access Control

Function	Returns	Description
`isAllowlisted(address addr)`	`bool`	Whether an address is on the allowlist
`isFeatureEnabled(FeatureFlag feature)`	`bool`	Whether a feature flag is enabled

Feature flag values:

Value	Feature	Description
`0`	SWAP	Enables/disables all swap operations
`1`	WITHDRAW	Enables/disables liquidity withdrawals
`2`	ALLOWLIST	When enabled, only allowlisted addresses can swap

Events

Event	Parameters	Description
`Swap`	`caller`, `tokenIn`, `tokenOut`, `amountIn`, `amountOut`, `fee`, `recipient`	Emitted on every successful swap
`TokenListingUpdated`	`token`, `isListed`	Token added or removed from listings
`TokenStatusUpdated`	`token`, `isSwappable`	Token swapping enabled or disabled
`FeeUpdated`	`oldFeeBasisPoints`, `newFeeBasisPoints`	Fee rate changed
`FeeRecipientUpdated`	`oldFeeRecipient`, `newFeeRecipient`	Fee recipient address changed
`FeatureFlagUpdated`	`feature`, `isEnabled`	Feature flag toggled
`AllowlistUpdated`	`addr`, `isAllowlisted`	Address added to or removed from allowlist

Error Reference

Error	Description
`SwapsCannotBePaused()`	Swap feature is disabled
`CannotBeZeroAddress()`	A required address parameter is the zero address
`CannotSwapSameToken(token)`	`tokenIn` and `tokenOut` are the same
`TokenNotListed(token)`	Token is not listed on the contract
`CannotBeZeroAmount()`	`amountIn` or `minAmountOut` is zero
`AddressNotInAllowlist(addr)`	Allowlist is enabled and caller is not allowlisted
`TokenMustBeSwappable(token)`	Token is listed but not currently swappable
`SlippageExceeded()`	Output amount is below `minAmountOut`
`TokenOutBalanceLessThanReservedAmount(token)`	Contract balance is less than the reserved amount
`AmountOutExceedsAvailableLiquidity(amountOut, availableLiquidity)`	Insufficient liquidity after accounting for reserves

Roles

The contract uses role-based access control. These roles are managed by the DEFAULT_ADMIN_ROLE holder.

Role	Permissions
`DEFAULT_ADMIN_ROLE`	Authorize upgrades, grant/revoke all roles (single holder, 2-step transfer)
`TREASURY_ROLE`	Withdraw liquidity, update reserved amounts
`CONFIGURE_ROLE`	List/unlist tokens, update fees, manage allowlist
`PAUSE_ROLE`	Pause/unpause swaps and withdrawals, enable/disable individual tokens

Swap Instruction

Program ID: 9vDwZVJXw5nxymWmUcgmNpemDH5EBcJwLNhtsznrgJDH (Key Addresses)

Parameters

Parameter	Type	Description
`amount_in`	`u64`	Amount of input token (in token’s native decimals)
`min_amount_out`	`u64`	Minimum acceptable output (slippage protection)

Required Accounts

Account	Type	Description
`pool`	Read-only	Liquidity pool PDA (seed: `"liquidity_pool"`)
`inVault`	Read-only	Vault PDA for input token
`outVault`	Read-only	Vault PDA for output token
`inVaultTokenAccount`	Writable	Token account holding input token reserves
`outVaultTokenAccount`	Writable	Token account holding output token reserves
`userFromTokenAccount`	Writable	User’s token account for input token
`toTokenAccount`	Writable	Destination token account for output token
`feeRecipientTokenAccount`	Writable	Fee recipient’s token account for input token
`feeRecipient`	Read-only	Fee recipient authority (validated against pool)
`fromMint`	Read-only	Mint of the input token
`toMint`	Read-only	Mint of the output token
`user`	Signer, Writable	User wallet signing the transaction
`tokenProgram`	Read-only	SPL Token Program
`associatedTokenProgram`	Read-only	Associated Token Program
`systemProgram`	Read-only	System Program

Transaction Structure

A Solana transaction contains one or more instructions. Each instruction specifies:

Program ID — the on-chain program to execute
Accounts — all accounts the instruction reads from or writes to
Instruction Data — the encoded parameters for the instruction

Account type	Description
Signer	Must sign the transaction
Writable	Will be modified by the instruction
Read-only	Only read from, not modified

Examples

Code samples for common swap scenarios

Quickstart

Get up and running in 10 minutes

Key Addresses

Program IDs and deployed addresses

Production Readiness

Helper functions and best practices

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Swap Function

Function Signature

Parameters

Preconditions

Fee Model

View Functions

Token State

Fee Configuration

Access Control

Events

Error Reference

Roles

Swap Instruction

Parameters

Required Accounts

Transaction Structure

What to read next

Examples

Quickstart

Key Addresses

Production Readiness

​Swap Function

​Function Signature

​Parameters

​Preconditions

​Fee Model

​View Functions

​Token State

​Fee Configuration

​Access Control

​Events

​Error Reference

​Roles

​Swap Instruction

​Parameters

​Required Accounts

​Transaction Structure

​What to read next

Examples

Quickstart

Key Addresses

Production Readiness

Swap Function

Function Signature

Parameters

Preconditions

Fee Model

View Functions

Token State

Fee Configuration

Access Control

Events

Error Reference

Roles

Swap Instruction

Parameters

Required Accounts

Transaction Structure

What to read next