Why Layer 2
Scaling Ethereum.
Why Layer 2 is a free Web3 & DApp Development Fundamentals 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 Web3 & DApp Development Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
The Scaling Problem
Ethereum can only process a limited number of transactions per second. When demand surges, blocks fill up and gas fees spike.
Layer 2 (L2) solutions exist to scale throughput without sacrificing the security of the base chain.
Layer 1 vs Layer 2
Layer 1 (L1) is the base blockchain like Ethereum. Layer 2 is a separate system that processes transactions off the main chain but settles back to it.
- L1: maximum security, limited throughput
- L2: high throughput, inherits L1 security
The Blockchain Trilemma
The trilemma says a chain struggles to be simultaneously scalable, secure, and decentralized at L1.
L2s sidestep this by handling scale off-chain while leaning on L1 for security and decentralization.
How Gas Fees Arise
Every operation costs gas, paid in ETH. Limited block space means users bid against each other, pushing fees up during congestion.
By moving execution off L1, L2s drastically cut the cost per transaction.
L1 swap fee: ~$15 during congestion
L2 swap fee: ~$0.05
// same action, far cheaperInheriting Security
The key insight of L2s: they do the heavy computation off-chain but post data or proofs to L1.
This lets them inherit Ethereum's security rather than bootstrapping a brand-new validator set.
Batching Transactions
L2s batch many transactions together and submit a single compressed summary to L1.
Hundreds of L2 transactions share the cost of one L1 submission, slashing per-user fees.
L2 collects 500 transactions
-> compress into 1 batch
-> post batch to L1
// cost split across all 500Rollups: The Dominant Approach
The leading L2 design is the rollup. Rollups execute transactions off-chain and post the resulting data to L1, where it can be verified.
We will explore Optimistic and ZK rollups in detail next lesson.
Other Scaling Approaches
Besides rollups, there are:
- State channels — off-chain payment channels
- Sidechains — independent chains with their own security
- Validiums — ZK proofs with off-chain data
Each trades off security, cost, and complexity differently.
Sidechains Are Not True L2
A sidechain runs in parallel with its own consensus and validators. It does not inherit L1 security.
If a sidechain's validators are compromised, funds can be lost — a key difference from rollups.
User Experience Improvements
For users, L2s mean near-instant confirmations and cheap fees, while still being able to bridge back to Ethereum.
This makes everyday actions like swaps, mints, and games economically viable on-chain.
Putting It Together
Layer 2s scale Ethereum by executing transactions off-chain and batching results to L1, inheriting its security while cutting fees dramatically.
Rollups lead the way, with sidechains and channels as alternatives. Next: how rollups actually work.
Quick Check
Test your Layer 2 fundamentals.
Recap: Why Layer 2
You learned that:
- L2s scale L1 by executing off-chain and settling on-chain
- They sidestep the trilemma and cut gas fees
- Batching shares L1 costs across many transactions
- Rollups inherit L1 security; sidechains do not
Next: rollups in depth.
Frequently asked questions
Is the “Why Layer 2” lesson free?
Yes — the full text of “Why Layer 2” is free to read here on the web, and the Web3 & DApp Development Fundamentals 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 Web3 & DApp Development Fundamentals course, upgrade to CoddyKit PRO.
What will I learn in “Why Layer 2”?
Scaling Ethereum. You practise Web3 & DApp Development Fundamentals 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 Web3 & DApp Development Fundamentals?
No prior experience is required. Web3 & DApp Development Fundamentals 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 “Why Layer 2” 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 Web3 & DApp Development Fundamentals lesson?
Yes. Every Web3 & DApp Development Fundamentals 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.
All lessons in this course
- Why Layer 2
- Rollups
- Bridging Assets
- Choosing a Layer 2