Swap with 1inch Aggregator

1inch is not an exchange. It is a router that shops your trade across hundreds of liquidity sources, and in Fusion mode it hands execution to professional resolvers who compete for your order in a Dutch auction.

That distinction matters because the three main modes on the interface — Classic, Fusion and Fusion+ — have different cost structures, different failure modes and different MEV exposure. Choosing the wrong one for your trade size is the most common way to leave money on the table.

1inch routes across 200+ liquidity sources on 13+ chains. For a large swap in a deep pair, splitting across venues genuinely beats any single pool. For a tiny swap, the extra gas of a split route can cost more than the price improvement it buys.

What you'll need (prerequisites)

• Self-custodial wallet (MetaMask, Rabby, etc.)
• ETH or native gas token
• Tokens to aggregate swap with
• Familiarity with transaction approvals

Classic, Fusion and Fusion+ — pick the right one

Classic swaps go through the 1inch Aggregation Protocol. Its Pathfinder algorithm splits your order across pools and venues to reduce slippage, and you submit the resulting transaction yourself. You pay gas, you pay the underlying pool fees, and your transaction sits in the public mempool where it can be sandwiched.

Fusion inverts that. You sign an off-chain intent — "I will give X, I want at least Y" — rather than a transaction. Approved resolvers then compete to fill it through a Dutch auction in which the rate on offer improves over a short window. The resolver pays the gas and settles on-chain. Because nothing of yours is broadcast to the mempool, the front-running surface for eligible swaps largely disappears.

Fusion+ extends the intent model across chains. You swap on one chain and receive on another, settled through escrow contracts rather than by minting a wrapped bridge token. This removes the wrapped-asset and bridge-custody risk that dominates cross-chain incidents, at the cost of a longer settlement window than a same-chain fill.

There are also limit orders, which sit off-chain until fillable. They cost nothing while resting and are the right tool when you have a price in mind and no urgency.

Step-by-step

1. Step 1: Reach the app from a bookmark and connect

   Aggregator front-ends are a favourite phishing target because users arrive expecting to approve token allowances. Type the address yourself the first time and bookmark it. Connect your wallet and approve the connection signature; it moves nothing.

2. Step 2: Select the network and the token pair — by contract address

   Choose the chain, then set the input and output tokens. For anything other than a blue-chip asset, paste the contract address rather than picking from a search result: token lists contain near-duplicate tickers, and a swap into the wrong contract is unrecoverable. Cross-check the address against the project's own site or a block explorer.

3. Step 3: Choose Classic, Fusion or a limit order

   Use Fusion when it is available for your pair and you want MEV protection with the gas cost priced into the quote. Use Classic when Fusion has no resolver coverage for the pair, or when you need a deterministic, immediate on-chain fill. Use Fusion+ when the destination is a different chain. Use a limit order when your target price is not the current price.

4. Step 4: Read the quote against a second source

   Before approving anything, compare the quoted output against another aggregator or a direct pool quote. A quote that is dramatically better than everywhere else is usually a sign of a token with a transfer tax, a honeypot, or a stale price. The output amount, not the headline rate, is the number to compare.

5. Step 5: Set slippage deliberately

   Slippage tolerance is your maximum acceptable difference between quoted and executed output. Too tight and the transaction reverts and you lose the gas; too loose and you are handing a sandwich bot a defined profit. Deep stable pairs tolerate a fraction of a percent; thin, volatile tokens need more — and if a token needs several percent to trade at all, its liquidity is the real problem. Check it first with a liquidity check.

6. Step 6: Approve the token — exact amount where you can

   Selling an ERC-20 requires an allowance for the 1inch router. Approve the amount you are actually swapping rather than an unlimited allowance. Where the token supports Permit2 or an ERC-2612 permit, use the signature route instead: it costs no separate transaction and is scoped and time-limited.

7. Step 7: Sign the intent or send the swap

   In Fusion you sign an order and wait — fills typically land quickly, but a Dutch auction is a process, not an instant. In Classic you send a transaction and wait for confirmation. In both cases the wallet prompt should show the token, the spender and the amount you expect; if it does not, reject it.

8. Step 8: Verify the received amount on-chain

   Open the transaction in the explorer and confirm the token that arrived is the contract you intended and the amount is within your slippage band. Save the hash. Every swap is a disposal for tax purposes in most jurisdictions, and reconstructing aggregator routes months later from wallet history alone is painful.

What you actually pay

The 1inch Aggregation Protocol does not add an on-top protocol fee to Classic swaps. What you pay is network gas plus the fees charged by the underlying liquidity sources it routes through — typically in the 0.05%–0.3% band depending on the pools involved. Those pool fees are already reflected in the quoted output amount, which is why comparing output amounts rather than advertised rates is the only reliable comparison.

In Fusion you do not pay gas directly. The resolver pays it and prices it into the rate they are willing to fill at, so it shows up as a slightly worse effective price rather than a separate line item. For small swaps on an expensive chain this is frequently cheaper overall than paying mainnet gas yourself; for large swaps in deep pairs the difference is marginal.

Third-party interfaces that route through 1inch may add their own fee. If you are not on the official 1inch front-end, assume there is a spread you cannot see and compare the output against the official app before signing.

Security pitfalls

• Verify the token contract, always. Ticker collisions are the single most common way people buy a worthless token. Paste the address from the project's official source.
• Never approve unlimited allowances by habit. Use exact amounts or permit signatures, and revoke what you no longer need — see revoking token approvals.
• Read the wallet prompt, not the website. The website shows what it wants you to see; the wallet prompt shows what you are actually signing. Spender address and amount are the two fields that matter.
• Treat a suspiciously good quote as a warning. Transfer-tax tokens and honeypots quote beautifully and cannot be sold.
• Avoid wide slippage on thin tokens. A 10% tolerance on an illiquid pair is an open invitation to a sandwich bot.
• Cross-chain takes time. A Fusion+ order is not instant. Do not assume a failure and start sending duplicate transactions while the first is still settling.
• Simulate before signing on unfamiliar contracts. Transaction-simulation tools show the expected balance changes before you commit.

Troubleshooting

• Transaction reverted with no obvious reason. Slippage exceeded during the block, or an allowance that was not set or was consumed. Raise slippage marginally, re-check the allowance, retry.
• Quote keeps changing while you read it. Normal — quotes refresh against live pool state. If it moves violently, the pair is thin and you should reduce size or split the trade.
• Fusion order not filled. No resolver found it profitable at your terms. Wait for the auction to improve the rate, adjust the amount, or switch to a Classic swap.
• Approval succeeded but the swap did not. Approval and swap are two separate transactions. Check that the second was actually broadcast and not silently rejected in the wallet.
• Received far less than quoted. Either the token charges a transfer tax on the receiving side, or you were sandwiched under an over-wide slippage setting. Check the token's contract for fee-on-transfer logic.
• Stuck pending on Ethereum. Speed up with replace-by-fee at the same nonce, or cancel with a zero-value self-transfer at that nonce.
• Cross-chain funds not arrived. Check the source-chain transaction first, then the settlement status in the app. Give it the documented window before escalating — and never re-send the swap in the meantime.

FAQ

Sources

• DEXTools — How to use 1inch for swaps: Classic, Fusion and limit orders (2026)
• DEXTools — 1inch explained: Pathfinder, Fusion and how the aggregator works (2026)
• Coin Bureau — 1inch exchange review: fees, pros and cons
• Crypto Adventure — 1inch review 2026: aggregation, Fusion execution and the real cost of a swap