> For the complete documentation index, see [llms.txt](https://document.sunprotocol.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://document.sunprotocol.io/en/smart-contracts/swap-contract.md).

# Swap Contract

SUN Swap provides direct USDT-to-SUN and SUN-to-USDT swaps and sends the resulting token to the caller.

### Read a quote first

| Function                 | Result                                                    |
| ------------------------ | --------------------------------------------------------- |
| `usdtbuysun(usdtAmount)` | Estimated SUN before user-selected slippage               |
| `sunsellusdt(sunAmount)` | Estimated USDT after the contract's 3% SUN sell-tax model |

Quotes use current router and pool state and do not guarantee execution. `SELL_TAX_BPS()` returns `300` with a denominator of `10,000`.

### Buy SUN

1. Query `usdtbuysun(usdtAmount)`.
2. Approve USDT to this contract.
3. Call `buySun(usdtAmount,slippageBps)`.

Buy slippage cannot exceed `MAX_BUY_SLIPPAGE_BPS()`—`200`, or 2%, in the published source.

### Sell SUN

1. Query `sunsellusdt(sunAmount)`.
2. Approve SUN to this contract.
3. Call `sellSun(sunAmount,slippageBps)`.

Sell slippage cannot exceed `MAX_SELL_SLIPPAGE_BPS()`—`500`, or 5%, in the published source. Execution depends on pool movement and SUN transfer tax.


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