Uniswap is a Review-First Swap and Verification Workflow

Preparing WETH for an Ethereum Contract Interaction

A USDC-to-WETH swap on Ethereum shows how review choices become a precise wallet request and a verifiable transaction.

Consider a wallet holding USDC on Ethereum and needing WETH for an existing contract interaction. USDC supplies the input, while ETH pays the network cost for a classic onchain route. Selecting WETH by its contract entry keeps a same-ticker asset on another network out of the quote. The review exposes the output estimate and execution limits before MetaMask, Coinbase Wallet, Rabby, or Uniswap Wallet receives anything to sign. Nothing has moved yet; the quote is a proposed transaction for the connected address and selected chain. Reading every field fixes the destination and shows which balance should change, turning opaque calldata into a trade with measurable boundaries.

Prerequisites Before the Quote

The complete prerequisite set includes a connected wallet, source balance, intended chain, token contract, and native gas token.

Wallet choice changes the confirmation surface, not the underlying chain state. Uniswap Wallet combines swapping and activity in one product. MetaMask exposes the target contract, value, and gas estimate in its extension flow. Coinbase Wallet supports Base directly, while Rabby emphasizes transaction decoding across EVM networks. WalletConnect supplies a connection path for many additional wallets. Each product still signs for the account that holds the input token, and each must point to the chain selected in the quote. Hardware-backed accounts add a device confirmation without changing the transaction that the network receives.

Network identity is numeric even when the interface shows names. Ethereum Mainnet uses chain ID 1, OP Mainnet uses 10, Polygon PoS uses 137, Base uses 8453, and Arbitrum One uses 42161. The gas asset follows the network: ETH covers Ethereum, Base, OP Mainnet, and Arbitrum One, while POL covers Polygon PoS. A token balance on one chain does not fund a swap on another.

What Does the Uniswap Review Screen Show?

The Uniswap review screen shows quoted output, fees, network cost, routing, price impact, and maximum slippage before wallet confirmation.

Quoted output states the expected receive amount at that moment, while maximum slippage defines the lowest acceptable execution amount. Price impact measures the change caused by the trade itself; it differs from later market movement. The fee line identifies swap charges, network cost estimates gas, and order routing reveals the pools or filler path behind the quote. Worked example: the changing inputs are a hypothetical quoted output of 2.000 WETH and a hypothetical maximum slippage of 0.50%. Multiplying 2.000 by 0.995 produces a minimum output of 1.990 WETH. A refreshed quote replaces those inputs before confirmation.

Approval Prompts and Their Separate Cost

Token approval and swap execution are separate authorizations, so the first transaction does not deliver the requested output asset. The related mechanics are detailed in Uniswap security.

An ERC-20 approval changes an allowance, permitting the designated contract to transfer up to the authorized amount. Uniswap commonly routes this through Permit2 and the Universal Router. The initial Permit2 approval is an onchain transaction and consumes gas. A subsequent typed-data signature grants the swap-specific permission without a network charge, and the swap itself requires a separate onchain confirmation. The common initial setup shows 3 wallet prompts, but only 2 of them create transaction hashes.

The Uniswap app limits its Permit2 signature approval to 30 days, after which the app requires a new signature. The underlying onchain allowance remains a separate state value until it changes. Approval alone moves no output token.

The approval amount shown by the wallet must meet or exceed the swap input. Returning swaps reuse eligible allowance, removing only the setup transaction from the flow.

Wallet Confirmation as the Execution Boundary

The wallet confirmation is the execution boundary because it binds the account, chain, contract call, value, gas, and signature.

Read the wallet request as a transaction rather than a repeat of the quote card. On EVM chains, the recipient field commonly points to a router or settlement contract, not the output token contract. The data field encodes the swap instructions, while value is nonzero when native ETH enters the call. An EVM address contains 20 bytes, written as 40 hexadecimal characters or 42 characters with the 0x prefix. EIP-55 mixed-case checksums help software detect typing errors. Permit2 signatures use EIP-712 typed data, binding the permission to a domain that includes the chain and verifying contract, as broken down in Uniswap guide.

From Confirm Click to Pending Transaction

Submitting a Uniswap confirmation turns a local wallet decision into a network transaction or, for UniswapX, a signed order.

Classic v2, v3, and v4 routes broadcast the swap and return 1 transaction hash. If an ERC-20 first needs Permit2 approval, that approval receives its own hash; the offchain signature does not. The common initial sequence therefore includes 3 wallet prompts, 2 onchain transactions, and 1 zero-gas signature. A submitted hash begins in pending state until the network includes or drops it. UniswapX differs: the wallet signs an order, and an open filler network submits settlement. Native ETH also requires 1 wrapping transaction before some UniswapX orders proceed. Closing the browser tab does not cancel a transaction that the wallet already broadcast.

The State Changes a Successful Swap Leaves Behind

A successful swap changes token balances, allowances, pool or filler settlement state, and the sender’s native balance for gas.

For a classic ERC-20 route, the router uses the approved allowance to collect the input, executes one or more pool hops atomically, and sends the output to the encoded recipient. Every hop succeeds together, or the transaction reverts and the token-exchange state changes disappear. The receipt still records gas consumed by a failed EVM transaction. A successful route decreases the input balance, increases the output balance, and reduces an active finite allowance as defined by the permission. Pool state also advances: v2 reserves update, v3 ticks and liquidity accounting update, and v4 records changes through its singleton architecture and configured hooks.

Token decimals determine explorer formatting. WETH uses 18 decimal places, while USDC uses 6, so equal-length raw integers can represent very different displayed amounts.

Explorer Evidence After Settlement

A block explorer verifies settlement through the transaction receipt, token-transfer logs, block inclusion, gas charge, and connected wallet address.

Select View on Explorer from the interface or open the hash from wallet activity. Etherscan covers Ethereum; Basescan, Arbiscan, and Polygonscan present the equivalent chain-specific record. On EVM networks, receipt status 1 means success, while status 0 means failure and applies no swap state changes. A transaction hash is 32 bytes, normally displayed as 64 hexadecimal characters plus a 0x prefix, for 66 characters total.

Match the explorer network, sender address, input transfer, output transfer, and gas asset to the review. Route contracts and intermediate transfers differ across execution paths, but those 5 anchors establish whether the intended wallet received the intended asset. If activity shows only an approval hash, the allowance changed but the swap has not occurred. Return to the interface and complete the separate swap request; the explorer then shows a second hash for execution.

Recovering From the Wrong-Network Setup Error

Matching the wallet chain to the source balance resolves a wrong-network setup, after which the interface must rebuild the quote.

Suppose USDC appears in the portfolio but the swap form reports no usable balance. First compare the token’s network badge with the wallet’s active chain. Ethereum Mainnet is chain ID 1, Base is 8453, OP Mainnet is 10, Polygon PoS is 137, and Arbitrum One is 42161. Switch the wallet and interface to the chain that actually holds the token, reconnect if requested, and reselect both assets. The prior quote belongs to the prior chain and route.

Crosschain swapping is a separate choice. When the interface deliberately shows different source and destination networks, it assembles a route through Across alongside Uniswap routing. That workflow adds bridging fees and a destination-chain result; correct a same-network setup error before selecting it.

Advanced Route and Receipt Edge Cases

Advanced route reading starts by identifying whether the quote uses classic Uniswap pools, UniswapX fillers, or native-token wrapping.

A classic path traverses one or more v2, v3, or v4 pools and shows intermediate ERC-20 transfers that never enter the user’s wallet. Uniswap v3 defines 4 pool fee tiers: 0.01%, 0.05%, 0.3%, and 1%; v4 permits a broader fee design, including dynamic fees configured by pool logic. The fee line follows the chosen route, so a multi-hop path can combine more than 1 pool’s fee and still present 1 quoted output.

An UniswapX fill places the filler and settlement contract in the explorer record, so its transfer graph differs from a direct pool swap. Routes with native ETH wrap it into WETH when ERC-20 handling is required, while token-to-ETH paths unwrap WETH before delivery. Read those events against the route label shown before confirmation. Explorer traces describe execution mechanics; wallet balance changes confirm the user-facing outcome.