Blockchain Smart Contracts with Solidity · Lesson

AMMs and Liquidity Pools

Understand how Automated Market Makers (AMMs) like Uniswap function and how liquidity pools enable decentralized trading.

AMMs and Liquidity Pools is a free Blockchain Smart Contracts with Solidity lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Blockchain Smart Contracts with Solidity learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Welcome to AMMs

Decentralized Finance (DeFi) has revolutionized how we trade assets. At its heart are Automated Market Makers (AMMs).

AMMs power decentralized exchanges (DEXs) like Uniswap, allowing users to swap tokens without traditional buyers and sellers.

Instead of matching orders, AMMs use mathematical formulas and liquidity pools.

Order Books vs. AMMs

Traditional exchanges use order books, where buyers and sellers list their desired prices. Trades only happen when bids and asks match.

Order Books: Centralized, requires matching orders, can suffer from low liquidity.
AMMs: Decentralized, uses liquidity pools, always offers a price determined by a formula.

AMMs solve the liquidity problem for many token pairs on a blockchain by always providing a market.

The Power of Liquidity Pools

An AMM's backbone is the liquidity pool. This is a collection of two or more tokens locked in a smart contract.

For example, a common pool might hold ETH and a stablecoin like DAI. Users can swap between these tokens directly from the pool.

These pools are funded by individuals called Liquidity Providers (LPs).

Meet the Constant Product Formula

Most AMMs, like Uniswap, use the constant product formula: x * y = k.

x is the quantity of the first token.
y is the quantity of the second token.
k is a constant product that must remain unchanged after a trade.

When you swap tokens, the quantities of x and y change, but their product k stays the same, determining the new price ratio.

How to Become an LP

Liquidity Providers (LPs) deposit an equal value of two tokens into a liquidity pool. For example, $1000 worth of ETH and $1000 worth of DAI.

In return, LPs receive Liquidity Pool (LP) tokens. These tokens represent their share of the pool.

LP tokens can be redeemed later to withdraw your original deposit plus any accumulated fees.

Adding Liquidity in Practice

When an LP adds liquidity, they increase the total supply of x and y in the pool, which also increases the constant k.

The AMM smart contract ensures that tokens are added in the correct ratio to maintain the pool's balance and prevent immediate price changes.

This process makes the pool deeper, allowing for larger trades with less price impact.

Swapping Tokens

When a user wants to swap Token A for Token B, they send Token A to the liquidity pool.

The AMM's smart contract then calculates how much Token B to give back, based on the x * y = k formula.

The pool's balance shifts, and the price of the tokens adjusts automatically according to the formula.

Code Example: Simulating a Swap

Let's see a simplified Solidity contract that simulates how an AMM might perform a swap using the constant product formula.

This example demonstrates the core calculation and reserve update.

pragma solidity ^0.8.0;

contract SimpleAmmSwap {
    uint public tokenXReserve = 1000 * 10**18; // 1000 tokens (e.g., ETH) with 18 decimals
    uint public tokenYReserve = 1000 * 10**18; // 1000 tokens (e.g., DAI) with 18 decimals
    uint public k = tokenXReserve * tokenYReserve;

    // Simulate a swap from Token X to Token Y
    // For simplicity, no actual token transfers, just reserve updates.
    function swapXForY(uint amountInX) public returns (uint amountOutY) {
        require(amountInX > 0, "Amount in must be positive");
        
        // Calculate new reserves and output amount
        uint newXReserve = tokenXReserve + amountInX;
        uint newYReserve = k / newXReserve;
        amountOutY = tokenYReserve - newYReserve;

        require(amountOutY > 0, "Not enough liquidity for swap");

        // Update reserves
        tokenXReserve = newXReserve;
        tokenYReserve = newYReserve;

        // Note: In a real AMM, actual token transfers would occur here.
    }

    // A getter to check current reserves
    function getReserves() public view returns (uint, uint) {
        return (tokenXReserve, tokenYReserve);
    }
}

Understanding Impermanent Loss

One major risk for LPs is impermanent loss. This occurs when the price of the assets in the liquidity pool changes relative to when you deposited them.

If the price ratio diverges significantly, the value of your tokens withdrawn from the pool might be less than if you had simply held them outside the pool.

It's called "impermanent" because the loss only becomes permanent if you withdraw your liquidity before the prices return to their original ratio.

LP Fees and Rewards

Despite impermanent loss, LPs are incentivized by earning a share of the trading fees generated by the pool.

Each time a trade occurs, a small percentage (e.g., 0.3%) of the swapped amount is added to the liquidity pool.

These fees accumulate in the pool and are distributed proportionally to LPs when they withdraw their liquidity, compensating them for providing capital and taking on impermanent loss risk.

Quick Check: AMM Basics

Test your understanding of Automated Market Makers and Liquidity Pools.

Recap: AMMs & Liquidity Pools

We've explored how Automated Market Makers (AMMs) provide decentralized trading by using liquidity pools instead of traditional order books.

Key takeaways:

AMMs use formulas like x * y = k to determine prices.
Liquidity Providers (LPs) fund pools and earn trading fees.
Impermanent loss is a risk for LPs due to price divergence.

Understanding these concepts is vital for navigating the DeFi landscape!

Frequently asked questions

Is the “AMMs and Liquidity Pools” lesson free?

Yes — the full text of “AMMs and Liquidity Pools” is free to read here on the web, and the Blockchain Smart Contracts with Solidity course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Blockchain Smart Contracts with Solidity course, upgrade to CoddyKit PRO.

What will I learn in “AMMs and Liquidity Pools”?

Understand how Automated Market Makers (AMMs) like Uniswap function and how liquidity pools enable decentralized trading. You practise Blockchain Smart Contracts with Solidity with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Blockchain Smart Contracts with Solidity?

No prior experience is required. Blockchain Smart Contracts with Solidity on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “AMMs and Liquidity Pools” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Blockchain Smart Contracts with Solidity lesson?

Yes. Every Blockchain Smart Contracts with Solidity lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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