When Reversing a Cross-Chain Swap, Check Pool Depth

Reverse swaps can return less than you expect because each direction meets different pool depth and price impact. A quote for A to B does not promise that B to A will undo the trade.

A cross-chain aggregator compares available routes between assets on different networks. For example, thor swap brings that route comparison into one interface; its quote depends on the direction and amount you enter.

Why does the reverse quote change?

Each pool holds reserves of two assets, and a trade changes their balance. The pool’s pricing curve means a larger trade gets a worse rate as it uses more of the available depth.

Say a pool has 100 units of A and 10,000 of B, with no fees for this illustration. Swapping 10 A returns about 909 B; swapping those 909 B back returns about 8.3 A. The difference comes from moving along the curve twice, not from a simple reversed exchange rate.

Cross-chain routes may use more than one pool, so each leg adds its own price impact and cost. THORChain’s swap formula shows how pool balances and trade size determine output; the same direction check matters when comparing routes in thor swap.

What should you compare in the quote?

Compare the final amount you receive for the same input, in each direction. A quoted rate alone can hide the effect of pool depth, network fees, and any service fee on that route.

Look for the route’s price impact, which estimates how much your trade shifts the pool price. Then check the minimum output: this is the least the swap will deliver before it fails, based on your slippage setting. Slippage is the allowed gap between the quote and the executed result.

Pool depth can change between quotes as other trades arrive. THORChain’s public pool data reports live pool depths, which helps explain why a route’s reverse quote may change even when the asset pair stays the same.

How do you check before swapping?

Use the route and amount you actually plan to trade, then compare both directions separately.

1. Enter the asset you will send, the asset you need, and the exact amount.
2. Record the quoted output, route, price impact, network costs, and minimum output.
3. Reverse the asset pair and enter the amount you would receive; read the new quote rather than inverting the first rate.
4. If the result is poor, compare another route or reduce the amount, then request a fresh quote before approving.

For a one-time task, proceed only when the minimum output still meets your need after costs. If it does not, lower the trade size or wait for deeper liquidity, then quote again.