# Swap Direction

Understanding X→Y vs Y→X swaps in DLMM. Token ordering determines swap direction and affects how you interact with pairs.

### Token Ordering in DLMM

In every pair:

* **Token X**: The token with the smaller address (sorted)
* **Token Y**: The token with the larger address
* This ordering is **permanent** and **automatic**

```typescript
// Example ordering
TokenX: "0x2::sui::SUI"        // Smaller address
TokenY: "0xabc...::usdc::USDC" // Larger address

// SUI is always X, USDC is always Y in this pair
```

### Understanding Swap Directions

#### X→Y Swap (xtoy = true)

* Selling Token X
* Buying Token Y
* Price moves UP (more Y per X)

#### Y→X Swap (xtoy = false)

* Selling Token Y
* Buying Token X
* Price moves DOWN (less Y per X)

### Checking Token Order

```typescript
const pair = await sdk.Pair.getPair(pairAddress);

console.log("Token X:", pair.tokenXType);
console.log("Token Y:", pair.tokenYType);

// Determine what xtoy means for this pair
if (pair.tokenXType.includes("SUI")) {
  console.log("xtoy=true: Sell SUI for USDC");
  console.log("xtoy=false: Sell USDC for SUI");
}
```

### Common Patterns

#### Swap by Token Type

```typescript
async function swapTokens(
  pair: LBPair,
  inputToken: string,
  amount: bigint
) {
  // Determine direction based on input token
  const xtoy = inputToken === pair.tokenXType;
  
  return await sdk.Swap.prepareSwap(pair, {
    amount,
    xtoy
  });
}
```

#### User-Friendly Wrapper

```typescript
// Helper for intuitive swapping
async function swap(
  pair: LBPair,
  fromToken: string,
  toToken: string,
  amount: bigint
) {
  // Validate tokens belong to pair
  const hasTokens = 
    (fromToken === pair.tokenXType || fromToken === pair.tokenYType) &&
    (toToken === pair.tokenXType || toToken === pair.tokenYType);
    
  if (!hasTokens) {
    throw new Error("Invalid token pair");
  }
  
  // Set direction
  const xtoy = fromToken === pair.tokenXType;
  
  return await sdk.Swap.prepareSwap(pair, {
    amount,
    xtoy
  });
}
```

### Price Movement

```typescript
// How swaps affect price
if (xtoy) {
  // Selling X for Y
  // Depletes Y reserves in bins
  // Price moves to higher bins
  // X becomes cheaper relative to Y
} else {
  // Selling Y for X
  // Depletes X reserves in bins
  // Price moves to lower bins
  // X becomes more expensive relative to Y
}
```

### Quick Reference

| Want to   | Token In | Token Out | Use           |
| --------- | -------- | --------- | ------------- |
| Buy SUI   | USDC (Y) | SUI (X)   | `xtoy: false` |
| Sell SUI  | SUI (X)  | USDC (Y)  | `xtoy: true`  |
| Buy USDC  | SUI (X)  | USDC (Y)  | `xtoy: true`  |
| Sell USDC | USDC (Y) | SUI (X)   | `xtoy: false` |

### Common Mistakes

```typescript
// ❌ Wrong: Assuming token order
const tx = await sdk.Swap.prepareSwap(pair, {
  amount,
  xtoy: true // Assumes first token is X
});

// ✅ Correct: Check actual order
const sellingTokenX = inputToken === pair.tokenXType;
const tx = await sdk.Swap.prepareSwap(pair, {
  amount,
  xtoy: sellingTokenX
});
```

### Related Topics

* [Execute Swap](/integration/dlmm/typescript-sdk/swap-operations/execute-swap.md) - Perform swaps
* [Get Single Pair](/integration/dlmm/typescript-sdk/trading-pairs/get-single-pair.md) - Check token order
* [Calculate Swap Output](/integration/dlmm/typescript-sdk/swap-operations/calculate-swap-output.md) - Preview results


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