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Before signing an Ethereum swap, verify the site and connected wallet, check both token contract addresses, review the quote and its minimum-output protection, and inspect any separate token approval. Stop if the wallet prompt is unexpected or unreadable. A valid signature authorizes a transaction; it does not guarantee a favorable result or that the result will match your economic goal.
Use this checklist before you sign
Work through these checks in order. If a detail in the wallet differs from what the swap interface led you to expect, do not sign until you understand the discrepancy. Ethereum.org recommends reviewing transaction details and warns that phishing sites can imitate legitimate interfaces; its security and scam prevention guide also advises never sharing a recovery phrase.
- Confirm the site and wallet. Open the exchange through a bookmark or another source you already trust rather than an unsolicited message or support link. Check that the wallet connected is the one you intend to use. A familiar-looking interface is not proof that the domain is genuine.
- Identify each token by its contract address. Compare the full address of the input and output token with the token issuer’s official information. A token name or ticker alone is not unique and can be copied. A reputable block explorer or exchange listing can provide a secondary clue, but should not replace the issuer’s source. See Ethereum.org’s guide to identifying scam tokens.
- Check the trade details. Confirm the input token, amount, output token, estimated output, fees, and any price-impact warning. Ethereum.org’s token swap guide says to review the exchange rate and fees before confirming.
- Understand the output floor. Read the slippage tolerance and minimum amount received, if the interface shows them. Make sure you understand how much less than the estimate you are willing to accept. Stop if the tolerance is unfamiliar or the quote changes unexpectedly.
- Inspect a separate token approval. If the wallet asks for an ERC-20 approval before the swap, verify the spender address and the amount of token it may transfer. An approval is a spending permission, not the swap itself. Prefer the smallest usable allowance rather than unlimited access when the wallet or interface gives you that choice.
- Read the wallet’s final prompt. Check that its decoded transaction details correspond to the swap you intend and that the spender or recipient is expected. Do not sign raw or otherwise unreadable data, an unexplained recipient or contract, unrelated permissions, or a prompt that contradicts the interface unless you can independently understand it.
- Decide whether the trade is worth proceeding with. Treat a severe price-impact warning as a reason to pause. You can reduce the trade size, compare other routes, or abandon the transaction instead of overriding the warning.
- Check the result independently. After signing, use a trusted block explorer to inspect the transaction status and result. A failed transaction can still consume gas; a completed transaction is ordinarily irreversible on Ethereum.
What is slippage, and what does minimum output protect?
Ethereum.org defines slippage as “the difference between your expected exchange rate and the actual rate.” In practical terms, a displayed quote is an estimate at the time it is shown. The swap executes against pool conditions when the transaction is processed, and those conditions can change. As a result, the executed rate and amount received may differ from the estimate.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsA slippage tolerance describes how much adverse movement the swap will accept under the interface’s terms. A minimum-output value expresses a floor for the amount you will receive. Review the value shown by the particular wallet or exchange rather than assuming every interface presents the setting in the same way. If you cannot tell what the displayed tolerance or minimum means, do not approve the transaction on guesswork.
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A loose tolerance can allow a materially worse fill than the quote suggested. A stricter floor can instead mean the swap does not execute if conditions move beyond the allowed range. The right decision depends on whether the possible output still makes sense to you; the objective is to know the accepted floor before signing, not simply to make the transaction go through.
ERC-8377, titled Reference-Relative Slippage Bounds, proposes a different way to define bounds: compare execution with a reference price independent of the venue being traded, distinguish expected non-adversarial costs such as pool fees and modeled price impact from adverse deviation, and optionally include a deadline. It is a proposal, not a feature readers should assume ordinary wallets or swaps already implement.
How approvals differ from swaps
Many ERC-20 swaps involve two distinct actions: permission for a spender to move a token, followed by the trade itself. An ERC-20 allowance sets how much of a token a spender is allowed to transfer. The approval does not itself exchange the token, and approving a token is not the same as confirming the swap. The Ethereum Foundation’s discussion of blind signing and transaction uncertainty covers the risks around unclear transaction details and token approvals.
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For an approval prompt, check both who can spend and how much they can spend. An unlimited allowance can leave the permitted amount available to the spender beyond the immediate trade. That creates a risk if the spender or interface is malicious or compromised. Where an interface permits it, a limited allowance sized for the intended use reduces the amount of access granted. Do not treat a familiar token name or a plausible-looking request as a substitute for checking the spender.
Some wallets and applications may present transaction details in more or less human-readable form. Ethereum Foundation material describes clear signing as an effort to make structured transaction descriptions legible, including review on a secondary device, but support varies among wallets and applications. A hardware wallet is optional; it is not a guarantee that every swap detail will be displayed clearly or that a fake token will be detected.
When a price-impact warning should stop the trade
Price impact concerns how much the trade itself moves the price in the pool. Thin liquidity can make a trade move that price sharply, so a large order relative to available liquidity can have a much worse effective rate than the initial quote. A warning is not an inconvenience to click past: compare the amount you plan to trade with the output and fees you would actually accept.
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If the warning is severe, the practical choices are to reduce the trade size, compare available routes at the same time and for the same input amount, or cancel. Compare the quoted output after fees, price impact for your intended trade size, slippage or minimum-output controls, requested spender and allowance, wallet-readable details, and network or gas costs. Quotes can change as market and pool state change, so comparisons made at different times may not be like-for-like. The available guidance identifies these as relevant comparison factors but does not endorse a particular venue.
The potential gap between authorization and outcome is not merely theoretical. In an October 5, 2026 Ethereum Foundation case study about an Aave/CoW collateral swap, a 99.9 percent price-impact warning appeared. The Foundation’s account says the swap involved about $50.4 million in aEthUSDT value while the tokens received were worth about $36,000. These are approximate figures from one specific case, not typical swap-loss statistics. The useful lesson is to treat a striking warning and an output far from the intended result as reasons to stop, not as a routine cost of swapping.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What signing does—and does not—mean
There are two separate ways a transaction can fail to meet expectations. An intent mismatch means the transaction presented for signing is not the transaction the user thought they were approving. An outcome mismatch means the authorized transaction executes, but its result conflicts with the user’s economic goal. The Foundation’s October 2026 article uses these distinctions to explain why showing a transaction is not the same as guaranteeing the result.
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The distinction matters because a signature is not an assurance of a particular market outcome. Your review must cover both what the wallet says you are authorizing and the minimum result you are willing to accept. The Foundation describes native transaction assertions—mechanisms intended to constrain a transaction’s final outcome—as research, not a general safety feature already available across Ethereum wallets.
Ethereum.org states, “A transaction sent on Ethereum is irreversible.” In ordinary operation, after a swap is completed there is no general undo button. Before signing, verify the details carefully; after signing, check the status and result in a trusted explorer instead of relying only on a success message in the interface. If the transaction failed, account for the possibility that gas was still consumed.
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Warning signs that mean stop
- The site address came from an unsolicited message, or the page asks for your recovery phrase or private key. Never give either to a swap site or someone claiming to be support.
- A token’s name or symbol looks familiar, but its contract address does not match the issuer’s information.
- The quoted output, fees, price impact, slippage tolerance, or minimum received changed unexpectedly or cannot be understood.
- An approval names an unfamiliar spender or requests more access than you intend to grant.
- The wallet shows raw or unexplained data, an unexpected recipient, or permissions unrelated to the swap.
- A price-impact warning is severe, yet the trade only appears acceptable if you ignore it.
Do not sign first and investigate later. If any of these checks fails, disconnecting or closing the page is safer than approving a request you cannot explain.
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