Swapping on a Decentralized Exchange: What Can Go Wrong
Swapping on a Decentralized Exchange: What Can Go Wrong
Key takeaways:
- Slippage is the difference between the expected and actual price, and it can be reduced by manually adjusting the tolerance.
- Sandwich attacks are bot-driven attacks that take part of your value when slippage tolerance and order size are large enough, and the transaction is visible in the public mempool.
- A fake token with the same name is not the same token; check the contract address before confirming.
- Liquidity removal means the token becomes worthless, so check the lock period and the reputation of the locker contract.
- Risks are part of trading on a DEX, but it is your responsibility to understand and manage them.
The risks of decentralized exchanges are often mentioned, but rarely explained in concrete terms. When you swap tokens on a decentralized exchange, you are not trading with other people directly, but with an automated protocol that uses liquidity from pools. This brings advantages, but also specific pitfalls that can cost you if you do not know what to look for.
This article shows you exactly what can go wrong before you confirm a swap, and which checks are crucial. The goal is for you to understand the mechanics and make a better decision.
Slippage: When the Price Is Not What You Saw
Slippage is the difference between the price you see on the screen and the price you actually get. On a decentralized exchange, the price changes with every transaction, because the ratio of tokens in the pool changes. If your swap is large relative to the pool, or if the pool is shallow, the price can slip noticeably.
The problem arises when you use the automatic slippage tolerance that the exchange suggests. That value is often set wide to ensure the transaction goes through, but it means you can accept a much worse price than you planned. The solution is simple: manually set the tolerance to a small value, enough to cover normal fluctuations, but not extreme ones. If the transaction does not go through, that is better than accepting a bad price.
Sandwich Transactions: An Automatic Tax on Your Swap
A sandwich attack is a technique used by bots to profit from your transaction. When you send a swap, a bot sees it in the mempool, the waiting room for transactions. It then inserts its own transaction before yours, drives the price up, and then sells you the token at that higher price. Your transaction goes through at a worse price, and the bot sells right after you and pockets the difference.
This happens automatically, without any mistake on your part. You can reduce the risk by using an exchange with sandwich attack protection, or by setting a smaller slippage tolerance, because bots target transactions with wide tolerance. Also, avoid sending extremely large amounts in a single order, as that attracts bot attention.
Fake Token with the Same Name: Why the Ticker Is Not Proof
On a decentralized exchange, anyone can create a token with any name and ticker. This means you might see a token that has the same name as a well-known project, but it is not that token. A ticker like USDC or WBTC is not enough to confirm identity.
The key check is the contract address, compared against multiple independent sources (official documentation, curated token lists, block explorer), because even the official website can be spoofed. That address is unique and immutable. Before confirming a swap, compare the address with the project’s official source, such as their website or documentation. If the address does not match, it is a fake token, and the swap will give you a worthless token.
When choosing a token from an exchange list, also look at liquidity and transaction count. Fake tokens often have low liquidity and a short history.
Liquidity Removal: When Your Token Becomes Worthless
Liquidity is the fuel of a decentralized exchange. When you swap tokens, you are actually exchanging with a liquidity pool. If that pool disappears, there is no one to buy your token, and it becomes worthless.
Liquidity removal happens when LP position holders withdraw funds from the pool, either intentionally (rug pull) or because liquidity is already so low that even a moderate withdrawal leaves the pool practically worthless. A small pool also means high slippage even during normal swaps. Before swapping an unknown token, check whether the liquidity is locked, meaning it is blocked in a smart contract.
Locked liquidity means the creator cannot withdraw it temporarily, but check the lock period and the reputation of the locker contract. Keep in mind that locked liquidity does not protect against rug pulls through the mint function, hidden owner privileges, or mechanisms that block selling.
What to Check BEFORE Confirming a Swap
Before you click the confirm button, run a quick checklist. First, check the token’s contract address, not just the name and ticker. Second, look at liquidity: is it large enough for your swap and is it locked? Third, set the slippage tolerance to a small value instead of using the automatic one.
Fourth, check the token’s history: how long it has existed, how many transactions it has, and who the main holders are. If the token is only a few hours old and has a suspicious distribution, that is a risk. Fifth, use a block explorer to check the contract and ownership, token sniffer tools, and DEX aggregators with token lists.
These checks take a minute and significantly reduce common risks, but they do not eliminate them. Risks are part of trading on a DEX, but it is your responsibility to understand and manage them.
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Frequently Asked Questions
Is slippage always bad?
No, small slippage is normal, but large slippage can mean you are paying much more than you planned. Set the tolerance manually to a small value.
How do I spot a fake token?
Check the contract address against multiple independent sources, such as official documentation, curated token lists, and a block explorer. If the address does not match, it is a fake token, regardless of the name.
What is locked liquidity?
It is liquidity that is temporarily blocked in a smart contract, so the creator cannot withdraw it until the lock expires. Check the lock period and the reputation of the locker contract, because locked liquidity does not protect against rug pulls through the mint function or hidden owner privileges.
Are all decentralized exchanges the same?
No, they differ in sandwich attack protection, liquidity depth, and user experience. Research what features an exchange offers before using it.
How can I reduce the risk of sandwich attacks?
Set a small slippage tolerance, avoid huge swaps in a single order, and use an exchange that offers protection against such attacks.
Where can I find more information about security?
Look for more information in the protocol’s own documentation and independent sources, such as technical forums and smart contract analyses.