Router: Adding Liquidity

Key takeaway: The Router's addLiquidity adds the safety layer absent from raw pair.mint() calls: deadline enforcement, slippage protection via amountAMin and amountBMin, and optimal-amount calculation using UniswapV2Library.quote() to determine how much tokenB to deposit for a given tokenA at the pool's current ratio. Brand-new pairs let the user's desired amounts set the initial price; existing pairs match the current ratio and revert if both Desired amounts fall short of their Min thresholds. WETH wrapping (the addLiquidityETH variant) lets ETH-paired pools accept native ETH without forcing users to wrap manually.

What You Are Building

The Router's liquidity functions are the safe entry point for adding tokens to a Uniswap V2 pair. Users never interact with the pair contract directly. They call addLiquidity() or addLiquidityETH() on the Router, which handles optimal amount calculation, pair creation, token transfers, and LP minting. Getting these functions right means understanding why each step exists, what breaks without it, and how the Router protects users from common pitfalls.