Why does the rate not stay exactly 1:1?

The 0.30% LP fee always lowers the output by that fraction. Any imbalance in pool reserves also moves the rate slightly away from 1:1. A perfectly balanced pool with zero fees would give exactly 1:1.

Is there an arbitrage opportunity if the rate drifts?

On a real-money exchange yes; on testnet the LP fee plus gas usually exceeds the drift. The mechanic still works: if USDC/USDT prices diverge, arbitrageurs trade until the pool re-balances. On testnet this is mostly a learning exercise.

Why are there two stablecoins on testnet?

Two stablecoins let you test routing and pool behavior with stable-to-stable pairs that mimic mainnet patterns. They also exercise the star-routing logic where USDC and USDT are both core tokens and any new token paired against either is reachable.

Are testnet USDC and testnet USDT the same as mainnet USDC and USDT?

No. They are separate test tokens deployed only for Monad Testnet, with no economic value and no relationship to the real Circle USDC or Tether USDT. They share the brand for familiarity, not the issuer.

How to Swap USDC for USDT on Monad Testnet

4 min read · Updated 2026-04-27

Swap USDC for USDT when you want to test stablecoin pool slippage, switch brands for a downstream test, or hold USDT instead of USDC.

The route

Path: USDC → USDT.

Direct trade through the USDC/USDT stablecoin pool. Both sides are USD-pegged, so the rate sits close to 1:1. The only deviation comes from the 0.30% LP fee and any imbalance in reserves.

Step by step

Open PuddleSwap and connect your wallet to Monad Testnet (chain ID 10143).
Pick USDC as the input token and USDT as the output token.
Type the USDC amount you want to swap. The output USDT amount updates automatically based on the best route.
Check the slippage tolerance. The default is 1%; raise to 2-3% for thin pools, lower for deep pools.
Sign the ERC-20 approval first. This grants the router permission to pull USDC from your wallet and only needs to happen once per token.
Once the approval confirms, the Swap button activates. Click Swap and sign the transaction.
After one block, USDT appears in your wallet as an ERC-20 balance.

Slippage and fees

Stablecoin-to-stablecoin swaps have minimal price impact when reserves are balanced. The default 1% slippage is more than enough for most swap sizes; you can lower it if you want tighter execution.

All UniswapV2-style pools on PuddleSwap charge a 0.30% LP fee on the input side. PuddleSwap itself does not charge an app-level fee. Gas is paid in test MON.

About USDC

USD-pegged stablecoin issued for Monad Testnet. Stable rate, deep core-pair pools, claimable from the stable faucet. See the USDC token page for the full address, decimals, and live pools.

About USDT

USD-pegged stablecoin (testnet variant). Behaves like USDC for routing and pricing, separate brand for diversification testing. See the USDT token page for the full address, decimals, and live pools.

Open PuddleSwap to swap USDC for USDT now, or read about star routing for the full routing model.

FAQ

Why does the rate not stay exactly 1:1?: The 0.30% LP fee always lowers the output by that fraction. Any imbalance in pool reserves also moves the rate slightly away from 1:1. A perfectly balanced pool with zero fees would give exactly 1:1.
Is there an arbitrage opportunity if the rate drifts?: On a real-money exchange yes; on testnet the LP fee plus gas usually exceeds the drift. The mechanic still works: if USDC/USDT prices diverge, arbitrageurs trade until the pool re-balances. On testnet this is mostly a learning exercise.
Why are there two stablecoins on testnet?: Two stablecoins let you test routing and pool behavior with stable-to-stable pairs that mimic mainnet patterns. They also exercise the star-routing logic where USDC and USDT are both core tokens and any new token paired against either is reachable.
Are testnet USDC and testnet USDT the same as mainnet USDC and USDT?: No. They are separate test tokens deployed only for Monad Testnet, with no economic value and no relationship to the real Circle USDC or Tether USDT. They share the brand for familiarity, not the issuer.