How to build a DeFi yield aggregator?
Yearn Finance formulated an idea that remains relevant: users should not manually monitor dozens of protocols for the best APY. We design a vault that accepts a deposit, and the strategy automatically places funds in the best protocol, reinvests yield, and switches when conditions change. The user receives a yvToken and doesn't need to think about anything else. Our experience shows that building an aggregator means solving several unrelated engineering challenges simultaneously: an on-chain vault with multiple strategies, an off-chain keeper for automation, an APY comparison system with normalization, and gas optimization that doesn't eat up all the yield. We guarantee high code quality and security at every stage.
How is the multi-strategy vault architecture structured?
Basic ERC-4626 vault
ERC-4626 is the modern standard for tokenized vaults. It defines a unified interface: deposit(), withdraw(), convertToShares(), convertToAssets(). The vault issues shares (ERC-20 tokens), and the price per share increases as yield accumulates. The key advantage of ERC-4626 is compatibility: any protocol supporting this standard can use your vault as a building block. Yearn V3 reworked everything around it. Building a vault today means implementing ERC-4626.
// Minimal interface
interface IERC4626 {
function deposit(uint256 assets, address receiver) external returns (uint256 shares);
function withdraw(uint256 assets, address receiver, address owner) external returns (uint256 shares);
function totalAssets() external view returns (uint256);
function convertToShares(uint256 assets) external view returns (uint256);
function convertToAssets(uint256 shares) external view returns (uint256);
}
Multi-strategy allocation
One vault — several strategies. The vault distributes funds among them according to weights (allocator). Each strategy is a separate contract implementing the IStrategy interface with methods harvest(), report(), withdraw(). Typical strategies for a USDC vault:
| Strategy |
Base APY |
Additional Rewards |
Risk |
| Aave V3 lending |
~5% |
None |
Low (proven protocol) |
| Compound V3 |
~4-6% |
COMP (separate claim) |
Low |
| Curve 3pool |
~2-4% |
CRV, CVX |
Medium (gauge changes) |
| Morpho |
~6-8% |
None |
Medium (peer-to-peer layer) |
The allocator decides how much to keep in each strategy. The simplest approach is to put everything into the one with the highest APY. A more mature approach is diversification with max_allocation_per_strategy (no more than 50% in one protocol) and consideration of liquidity.
Why is ERC-4626 the foundation of a modern vault?
The standard allows easy integration with any DeFi protocol. A vault that complies with ERC-4626 can be used as a building block for other products: collateral in lending, backing for StableSwap, a component of a yield-bearing portfolio. We use the OpenZeppelin implementation for a reliable base.
Gas optimization for small positions
The harvest operation (claim rewards + swap + reinvest) costs $5-20 on Ethereum mainnet. For a vault with $10K TVL, daily harvest consumes 1-2% of annual yield. Solutions:
-
Batch harvesting: triggered when unrealized profit exceeds a threshold of gas cost × multiplier. If expected profit is $50 and harvest costs $15 — execute. If profit is smaller — wait.
- L2-first strategy: On Arbitrum or Base, gas per harvest is 100-500 times cheaper. A $50K TVL on Arbitrum can harvest hourly without losses. Gas savings for $1M TVL can reach $5000 per month.
- Gas optimization: batching via Multicall3, using ERC-2612 (permit), packed storage.
| Network |
Approx gas per harvest |
TVL for profitability |
| Ethereum |
$10-25 |
>$200K |
| Arbitrum |
$0.05-0.1 |
>$10K |
| Base |
$0.02-0.05 |
>$5K |
Why is APY comparison a nontrivial task?
The APY displayed on Aave, Compound, Curve is not the same metric. Aave: supplyAPY = (1 + supplyRatePerSecond)^(seconds_per_year) - 1, does not include AAVE emissions. Compound: supplyRate in wei per second, COMP reward separately. Curve + Convex: base APY from trading fees + CRV + CVX + extra rewards — totaling 4-5 streams. Morpho: APY higher than base due to peer-to-peer matching.
Normalization: convert all rewards to USD via Chainlink oracle, compute total_yield_per_day / tvl * 365. This gives a comparable APY. For forward-looking estimates, we use a 7-day moving average.
What risks and protections do we provide?
-
Strategy loss: a strategy may lose funds (exploit). The vault has a report() mechanism with emergency exit if losses exceed X%.
- Withdrawal queue: a user withdrawing $1M — first from free balance, then gradual withdrawal from strategies in priority order.
- Rugpull via governance: all strategy changes go through a 48-hour timelock. Emergency functions are limited to a pre-approved multisig.
What tools do we use?
Foundry for contracts and tests. OpenZeppelin (ERC-4626, AccessControl, ReentrancyGuard). The Graph for indexing events. Off-chain keeper: TypeScript + viem, deployed on Railway or VPS. Tenderly for simulation.
How do we work?
- Architecture and strategies (1 week): selecting protocols, allocation logic, gas threshold.
- Core vault + basic strategy (2 weeks): ERC-4626, Aave/Compound, keeper.
- Additional strategies (1 week per strategy): Curve, Morpho, Convex.
- APY engine + frontend data (1 week): normalization service, API.
- Audit (optional).
Timelines and cost vary: from 2 weeks to 3 months, price from $15,000 to $60,000 depending on number of strategies and networks. We give an exact estimate after agreeing on the technical specification.
What is included in the work
- Architecture and interface documentation.
- Source code for smart contracts and keeper.
- Tests (unit, integration, fuzzing) with >90% coverage.
- Deployment and operation instructions.
- Technical support during launch.
- Option to train your team.
We have over five years of DeFi development experience, delivered 30+ projects, and launched 10+ vaults on mainnet. Gas optimization and rebalancing are our core competencies.
Order a DeFi yield aggregator development — contact us to discuss the technical specification. Get a consultation on architecture and timelines.
DeFi Protocol Development
We design modular DeFi protocols where the math of stablecoins, liquidity, and oracles works flawlessly. Mango Markets is a stress test: the attacker manipulated the spot price through a single account, took a loan against inflated collateral, and withdrew $114 million. The oracle took the price from a single source without TWAP. Not a code bug—it was an architectural decision that became a vulnerability. Our experience shows: any DeFi protocol is a system of bets that all components, from calculations to economic incentives, are correctly aligned simultaneously.
We don't write code under the 'if it works, don't touch it' mindset. We model stress scenarios: cascading liquidations, depegs, flash loans. Only then do we build events that won't break the protocol.
Why are oracles a critical component of DeFi?
Most major DeFi hacks started with oracle manipulation. Let's break down the three layers we use in every project.
Spot price as oracle—not an option. Uniswap v2 spot price can be shifted by a flash loan in one transaction. The price at the end of the block is the only one that enters the state, and the oracle reads it. Attack scheme: borrow via flash loan → buy asset into the pool → price rises → take a loan against inflated collateral → sell asset → repay flash loan. One transaction.
TWAP as protection. Uniswap v3 observe() averages the price over a period (30 minutes). Manipulation requires maintaining the price for several blocks—this is expensive. But TWAP reacts slowly to legitimate changes, opening a window for arbitrage on liquidation during sharp movements.
Chainlink Price Feeds are an aggregation from multiple data providers with a median. Standard for lending. Problem: heartbeat 1–24 hours and deviation threshold 0.5%. If the price doesn't move, the feed may not update for a day. In volatile markets—lag.
| Oracle |
Mechanism |
Manipulation Protection |
Latency |
| Chainlink |
Median from independent providers |
High (decentralization) |
Up to 24h at 0% movement |
| Uniswap v3 TWAP |
Average price over N blocks |
High (hard to maintain) |
30 min – 1 h |
| Pyth Network |
Cross-chain low-latency |
Medium (dependent on publisher) |
Seconds |
In production, we use a two-tier check: Chainlink aggregator + Uniswap v3 TWAP as a verifier. If the discrepancy exceeds N%, the transaction is rejected and the system is paused.
How to protect a DeFi protocol from flash loan attacks?
Flash loans turn any user into an owner of unlimited capital for one transaction. Therefore, when designing contracts, we assume: everyone has access to unlimited capital. This completely changes the threat model.
Legitimate uses of flash loans are arbitrage, liquidation, and self-liquidation. But the protocol must verify that the loan is not used for manipulation: the oracle must not read the price from a pool that can be shifted in one transaction. We add checks on block.timestamp and minimum liquidity depth.
Key Components of DeFi Architecture
| Protocol Type |
Core Mechanism |
Main Risk |
| DEX (AMM) |
x*y=k or concentrated liquidity |
impermanent loss, oracle manipulation |
| Lending |
collateral ratio, liquidation |
bad debt during cascading liquidations |
| Yield aggregator |
auto-compounding strategies |
rug via strategy upgrade |
| Derivatives / Perps |
funding rate, mark price |
liquidation cascades, socialized losses |
| Liquid staking |
stETH-style rebasing |
depegging on mass unstake |
AMM: From x*y=k to Concentrated Liquidity
Uniswap v2 uses x * y = k. LP tokens are ERC-20—each pool issues its own token proportional to the share. Problem: liquidity is spread across the entire curve, most of it unused.
Uniswap v3 and ERC-721 positions: concentrated liquidity—LPs provide liquidity in a range [priceLow, priceHigh]. Capital efficiency up to 4000x for stable pairs. But ERC-721 breaks vault strategies built for ERC-20. Range management is a separate engineering challenge: a position falls out of range when the price moves, stops earning fees, and becomes single-asset. Protocols like Arrakis Finance automatically rebalance. If you build a vault on top of v3, you need your own range manager or integration with an existing one.
Slippage in v3 is calculated via sqrtPriceX96—96-bit fixed-point math. Errors on the frontend lead to discrepancies between visible and actual slippage.
Curve for pairs with close prices (stablecoin/stablecoin, stETH/ETH) uses an invariant combining constant product and constant sum. Lower slippage within the peg range. Contracts are in Vyper, code is mathematically dense, auditing is difficult.
Lending Protocols: Collateral, Liquidation, Bad Debt
LTV defines the maximum loan against collateral. Liquidation threshold is the level for liquidation. The difference is the buffer for the liquidator. Typical example: LTV 75%, liquidation threshold 80%, bonus 5%. If the price drops 20%+, the position is open for liquidation.
Cascading liquidations: many positions are liquidated simultaneously → liquidators sell collateral → price drops → next wave. LUNA/UST 2022 is a classic cascade.
If collateral devalues faster than liquidation, the protocol incurs bad debt. Aave uses a Safety Module (staked AAVE), Compound uses reserves. Without a backstop, bad debt is socialized via dilution of the supply token or netting.
Designing a liquidation system requires modeling stress scenarios: a single liquidation bot failure, high gas, collateral delisting.
Yield Farming and Incentive Mechanics
Liquidity mining distributes governance tokens to LP providers. Problem: mercenary capital—farmers come, sell tokens, leave. TVL is illusory.
Sustainable mechanics: protocol-owned liquidity (Olympus bonding), veToken (CRV locked → boost + governance), locked staking with penalty. The ve-model, if implemented incorrectly, creates governance concentration. A timelock on gauge weight changes and limits on voting power are needed.
What Our DeFi Protocol Development Includes
- Architectural documentation: contract interaction diagrams, liquidation stress tests, oracle calculations.
- Implementation in Solidity 0.8.x with OpenZeppelin 5.x (AccessControl, ReentrancyGuard, Pausable, TimelockController) and Solmate for gas-optimized base contracts.
- Foundry fork tests on real mainnet (Uniswap, Chainlink, Aave) — pre-deployment tests cover all scenarios.
- Audit: at least two independent auditors for TVL over $1M. Code4rena or Sherlock for bug bounty.
- Deployment with Gnosis Safe 3/5 multisig + timelock 48–72 hours.
- Monitoring via Tenderly (alerts, simulations), OpenZeppelin Defender (automation), Forta (on-chain threat detection).
- Post-launch support: updates, patches, upgrades via proxy.
Our Expertise and Experience
We have been developing DeFi protocols since 2020, delivering 30+ projects with a combined TVL of over $150 million. Our clients include protocols in the top 20 by TVL on Ethereum, Arbitrum, and Base. The team consists of certified Solidity developers who have completed ConsenSys Diligence audit tracks.
DeFi basic principles that we apply in practice.
Timelines
- DEX with AMM (Uniswap v2 fork): 6–10 weeks
- Lending protocol (Aave-style, single collateral): 3–5 months
- Yield aggregator with multiple strategies: 2–4 months
- Full-fledged DeFi protocol with governance: 5–8 months including audit
Cost is calculated individually—contact us for a project estimate.
Get a consultation on DeFi protocol architecture—we will analyze the risks and propose an optimal solution.
