No.243
Euler EUL
build-your-own lending vault
🎭 a tidy vault-keeper who hands you the keys and says, here, make your own bank
💬 “Most lending apps decide which coins are allowed. I flipped it around: open a vault, set your own rules, lend whatever token you like. A thief once nearly emptied me in 2023, and I got every last coin back. I rebuilt to make that harder to repeat.”
- Euler is a lending app on Ethereum: deposit crypto to earn interest, or borrow against it, no bank involved.
- Its twist: anyone can open their own isolated market for almost any token, instead of waiting for a committee to approve it.
- 2023: a flash-loan attack drained ~$197M, then the attacker returned it all, a near-unheard-of ending.
- Supply is fixed at 27,182,818 EUL, the digits of Euler's number e. EUL is for governance voting.
📖 The Story
December 2021. A small team called Euler Labs, led by Michael Bentley, launched a lending protocol on Ethereum. Lending apps already existed, but they all worked from an approved list: a few blue-chip coins you could lend or borrow, and everything else was locked out. Euler asked a blunter question, why should anyone get to decide that for you?
Its answer was the isolated market. If you wanted to lend or borrow some niche token nobody else supported, you could open a vault for it yourself, set the rules, and keep its risk fenced off from everything else. The protocol handed users the keys instead of holding them.
March 13, 2023. An attacker used a flash loan to exploit a flaw and walked off with roughly $197 million in deposits, one of the worst DeFi hacks of the year. For a young protocol, it looked fatal.
Then something almost unheard-of happened. Over the following weeks, after public messages and on-chain negotiation, the attacker gave the money back. By April 3 the funds had returned and users were made whole. Most hacked protocols never see a cent again; Euler recovered nearly everything.
September 2024. Rather than limp on, the team rebuilt from the ground up as Euler v2, passing more than thirty security audits before relaunch. The vault-keeper had been robbed once, counted every coin back, and came back with thicker walls.
📊 Stats
Ratings are our editorial read for beginners, not live market data.
🧩 How it works
Euler is a DeFi smart-contract app, not a blockchain of its own. At heart each market is two-sided: lenders deposit a token into a vault and earn interest, while borrowers draw from that same vault against collateral and pay interest back. The clever part is modular: a piece called the Euler Vault Kit lets anyone spin up a fresh, self-contained vault for almost any token, and a connector wires those vaults together so deposits can be put to work. Each vault keeps its own risk in its own box.
🌗 Light & Shadow
- Permissionless and flexible: you can lend or borrow tokens that mainstream lending apps simply do not list
- Isolated vaults keep risk fenced off, so one shaky token is less likely to drag the whole pool down
- A rare comeback story, the 2023 hack ended with funds returned and a fully re-audited v2 (few protocols ever recover at all)
- That ~$197M hack is real history. The bigger the experiment, the more places a bug can hide (the funds came back, but that was luck plus negotiation, not a guarantee)
- Letting anyone open a market means some markets will be thin or risky, and that is on you to judge
- Smaller and less battle-tested than rivals like Aave; the modular design is powerful but a lot to learn for a beginner
🧬 Evolution lineage
Euler is not a fork or spin-off of another coin. It is an original DeFi lending token built on Ethereum. It shares a family with Aave and Compound, not by sharing code, but by doing the same job, lending. Its difference is letting anyone build their own customizable, isolated market.
🧭 Meet other friends
❓ FAQ
- What is Euler?
- A lending app that lives on Ethereum. You can deposit crypto to earn interest, borrow against it, or even open your own little lending market for almost any token, all without a bank in the middle. The EUL token is for voting on how it runs.
- Is Euler its own blockchain?
- No. Euler is a smart-contract app that runs on top of Ethereum, so it has no miners or validators of its own. It borrows Ethereum's security. EUL is an ERC-20 token, also deployed on chains like Arbitrum, Base and BNB Smart Chain.
- What happened in the 2023 hack?
- On March 13, 2023 an attacker drained about $197 million from Euler in a flash-loan exploit, one of the biggest DeFi hacks that year. Then something rare happened: weeks later the attacker returned the funds, and users were made whole.
- Why is the supply 27,182,818 EUL?
- It is a math joke. The protocol is named after the mathematician Euler, whose famous number e is about 2.7182818. The total supply copies those digits exactly. It is fixed for the first four years before any inflation can even be voted on.
⚠️ Not investment advice. All figures are for information only