Uniswap

Uniswap is the dominant on-chain DEX across Ethereum and L2s. V3 introduced concentrated liquidity — LPs allocate capital to specific price ranges instead of the full curve. V4 introduced a singleton PoolManager architecture with customizable hooks that modify pool behavior at every lifecycle point (swap, add/remove liquidity, donate).

What You Probably Got Wrong

AI agents trained before mid-2024 confuse V2, V3, and V4 patterns. These are the critical corrections.

• V3 concentrated liquidity is NOT V2 — V3 positions specify a tickLower and tickUpper price range. Liquidity outside the current tick earns zero fees. There is no "full range" default. If you want full-range, you must explicitly set tickLower/tickUpper to MIN_TICK/MAX_TICK (which is capital-inefficient).
• sqrtPriceX96 is not a price — V3/V4 store price as sqrt(price) * 2^96, a Q64.96 fixed-point number. To get the human-readable price: (sqrtPriceX96 / 2^96)^2. You must also adjust for token decimal differences. Getting this wrong produces prices off by orders of magnitude.
• Tick math uses int24, not uint256 — Ticks range from -887272 to 887272. Each tick represents a 0.01% price change. Tick spacing varies by fee tier: 1 (1bp), 10 (5bp), 60 (30bp), 200 (100bp). Positions must align to tick spacing boundaries.
• V4 is a singleton — one contract holds all pools — Unlike V3 (one contract per pool), V4's PoolManager holds all pool state. Pools are identified by a PoolKey (currency0, currency1, fee, tickSpacing, hooks address), not by a contract address. There is no pool factory in V4.
• V4 hooks are not optional middleware — Hooks are smart contracts attached to a pool at creation. The hook contract address encodes which callbacks it implements via specific bit flags in the leading bytes. You cannot add or remove hooks after pool creation.
• SwapRouter02 is the current V3 router, not SwapRouter — The original SwapRouter (0xE592...) is deprecated. Use SwapRouter02 (0x68b3...) which supports both V2 and V3 in a single interface. Even better: use UniversalRouter for V3+V4+Permit2 in one transaction.
• Fee tiers are in hundredths of a basis point — The fee parameter 3000 means 0.30%, not 30%. Common tiers: 100 (0.01%), 500 (0.05%), 3000 (0.30%), 10000 (1.00%).
• Permit2 replaces individual token approvals — Uniswap's UniversalRouter requires tokens to be approved to the Permit2 contract, not the router. You approve Permit2 once, then sign gasless permits per transaction.

Quick Start