Building Fuse: A DeFi Vault That Protects Your Portfolio While You Sleep

Published: January 2026

The Problem That Kept Me Up at Night

If you've ever staked crypto assets, you know the feeling. You wake up, check your portfolio, and see that your $10,000 position is now worth $6,000. The market crashed overnight, and you weren't there to react. You're left wondering: "What if I had set a stop-loss? What if there was a way to automatically protect my floor price?"

That's exactly the problem I set out to solve with Fuse.

This is what happens when you're not watching your portfolio 24/7

Fuse is a DeFi vault that automatically protects your staked assets by maintaining a hard floor price. You set your threshold once, and the smart contracts handle the rest. No more staying up all night watching charts. No more panic selling. Just set it and forget it.

What Makes Fuse Different?

Most DeFi protocols either:

• Lock your funds for months (no flexibility)
• Require constant monitoring (no automation)
• Don't protect against downside risk (no safety net)

Fuse combines the best of all worlds:

• Automated protection - Smart contracts monitor prices 24/7
• Flexible withdrawals - No lock-up periods, exit anytime
• Floor price guarantee - Your assets never drop below your threshold
• Yield generation - Still earn while protected

The six core features that make Fuse unique

The magic happens through a single trigger price. When the market price drops below your trigger, Fuse automatically swaps your volatile assets (like AVAX) to stablecoins (like USDC). When the price recovers above your trigger, it swaps back. It's like having a professional trader watching your portfolio, except it's a smart contract that never sleeps.

How It Works: The Technical Deep Dive

Let me walk you through how I built this. The architecture is modular, secure, and follows industry best practices.

The Core Architecture

Fuse is built on the ERC-4626 standard, which is the tokenized vault standard for DeFi. This means it's compatible with the entire DeFi ecosystem - you can use Fuse shares in other protocols, trade them, or use them as collateral.

The modular architecture of Fuse - each component has a specific responsibility

The system consists of three main layers:

1. Core Contracts (The Foundation)

• AutoSwapVault.sol - The main vault contract that handles deposits, withdrawals, and coordinates everything
• VaultStorage.sol - Manages the upgradeable storage layout (yes, the contracts are upgradeable!)
• VaultAccessControl.sol - Role-based permissions for security

2. Module Contracts (The Workers)

• SwapExecutor.sol - Handles all DEX swaps via Uniswap V3 with slippage protection
• PriceOracle.sol - Integrates with Chainlink for real-time price feeds
• UserSettingsManager.sol - Manages per-user configurations (trigger prices, slippage tolerance, etc.)
• CircuitBreaker.sol - Emergency pause mechanism if something goes wrong

3. Library Contracts (The Logic)

• VaultMath.sol - All the ERC-4626 share/asset calculations
• PriceLogic.sol - The single trigger price logic (when to swap, when not to)
• SafeSwap.sol - Slippage validation and safety checks

The Single Trigger Price Mechanism

This was the most interesting part to design. Instead of separate stop-loss and take-profit prices, Fuse uses a single trigger price that works bi-directionally:

If price < trigger → Swap to stablecoin (protect from loss)
If price > trigger → Swap back to volatile asset (re-enter market)

How the single trigger price works in both directions

This design prevents the "flip-flopping" problem where you might swap back and forth rapidly if prices hover around your threshold. There's a built-in buffer (0.5%) that prevents unnecessary swaps.

Security: Built From the Ground Up

When you're dealing with people's money, security isn't optional - it's everything. Here's what I implemented:

Reentrancy Protection

Every state-changing function uses OpenZeppelin's `ReentrancyGuard`. This prevents the classic reentrancy attacks that have drained millions from DeFi protocols.

Access Control

Role-based permissions ensure only authorized addresses can execute critical functions. There are four roles:

• Admin - Can update vault configuration
• Manager - Can update user settings
• Operator - Can execute auto-swaps (Chainlink Keepers)
• Upgrader - Can upgrade contracts (with timelock)

Oracle Manipulation Protection

Chainlink price feeds are great, but they can be manipulated or go stale. I added:

• Staleness checks (reject prices older than 1 hour)
• Price validation (reject prices that changed >50% in one update)
• Anomaly detection (flag suspicious price movements)

Slippage Protection

Users can set their own slippage tolerance (0.1% to 50%). The contract validates every swap to ensure it doesn't exceed this tolerance.

Multiple layers of security protect user funds

Testing: 238 Test Cases and Counting

I'm a firm believer that untested code is broken code. The test suite includes:

• Unit tests - Every function tested in isolation
• Integration tests - Testing how modules work together
• Fuzz tests - 259 random inputs per test to find edge cases
• Attack scenario tests - Simulating common DeFi exploits

The test coverage is 96%+, and I'm still adding more tests as I think of edge cases.

Comprehensive test coverage ensures reliability

The Frontend: Making It Beautiful

A smart contract is only as good as its user interface. I spent significant time building a premium, minimal frontend using Next.js 16, React 19, and Framer Motion.

The Fuse dashboard - clean, intuitive, and responsive

Key Features

Real-time Price Monitoring

• Live price updates every 5 seconds
• Visual indicators when you're close to your trigger
• Historical price charts (coming soon)

One-Click Deposits

• Deposit native AVAX or wrapped WAVAX
• Automatic approval handling
• "Use Max" button for convenience

Flexible Settings

• Set your trigger price with quick presets (-5%, -10%, -20%)
• Adjust slippage tolerance with a slider
• Toggle auto-swap on/off anytime

Mobile Responsive

• Works beautifully on all screen sizes
• Touch-optimized interactions
• Progressive enhancement

The landing page features smooth animations, interactive background elements, and a premium feel that matches the quality of the smart contracts underneath.

The full landing page with all sections

Challenges I Faced (And How I Solved Them)

Challenge 1: The Flip-Flop Problem

Problem: If the price hovers exactly at your trigger, the contract might swap back and forth rapidly, wasting gas and causing losses.

Solution: Implemented a price buffer (0.5%) around the trigger. The effective trigger for swapping to stable is `trigger - 0.5%`, and for swapping back it's `trigger + 0.5%`. This creates a "dead zone" that prevents rapid oscillations.

Challenge 2: Oracle Staleness

Problem: Chainlink price feeds can go stale or be delayed, leading to incorrect swap decisions.

Solution: Added comprehensive staleness checks. The contract rejects any price that's older than 1 hour, and flags prices that changed more than 50% in a single update (likely an error or manipulation).

Challenge 3: Gas Optimization

Problem: DeFi users are sensitive to gas costs. Every extra operation costs money.

Solution:

• Used custom errors instead of string reverts (saves ~50% gas on failures)
• Packed structs to minimize storage reads
• Made functions `pure` or `view` where possible
• Cached storage variables in memory

The result? Deposits cost ~85k gas, withdrawals ~95k gas, and swaps ~180k gas. Competitive with other DeFi protocols.

Challenge 4: Testing Complex Interactions

Problem: Testing a system with multiple contracts, external dependencies (Chainlink, Uniswap), and user interactions is complex.

Solution: Built comprehensive mock contracts for Chainlink and Uniswap. This allows testing all scenarios, including edge cases and attack vectors, without needing real external contracts.

The testing infrastructure - mocks, fuzz tests, and integration tests

What I Learned

This project taught me more about DeFi, smart contract security, and system design than any tutorial or course could. Here are the key takeaways:

1. Security is a Mindset, Not a Feature

You can't bolt security on at the end. Every design decision needs to consider security implications. I spent as much time thinking about attack vectors as I did implementing features.

2. Modularity is Your Friend

Breaking the system into separate contracts (modules, libraries, core) made testing easier, reduced complexity, and allowed for easier upgrades. When I found a bug in the swap logic, I only needed to fix one contract.

3. User Experience Matters in DeFi

Most DeFi protocols have terrible UX. I wanted Fuse to be different. The frontend is intuitive, responsive, and beautiful. Users shouldn't need a PhD to protect their assets.

4. Documentation is Code

I wrote extensive NatSpec comments, created architecture diagrams, and documented every design decision. Future me (and any auditors) will thank present me.

5. Testing is Not Optional

I caught dozens of bugs during testing that would have been catastrophic in production. The time spent writing tests saved me from potential disasters.

The Tech Stack

For those interested in the technical details:

Smart Contracts:

• Solidity 0.8.24
• Foundry (testing framework)
• Hardhat (deployment)
• OpenZeppelin Contracts v5.0
• Chainlink Price Feeds
• Uniswap V3

Frontend:

• Next.js 16 (App Router)
• React 19
• TypeScript
• Tailwind CSS 4
• Framer Motion (animations)
• Ethers.js v6 (Web3 interactions)

Backend:

• MongoDB (for invitation emails)
• Next.js Server Actions

Testing:

• Foundry (Solidity tests)
• 238 test cases
• 96%+ coverage
• Fuzz testing

The complete technology stack powering Fuse

Current Status and Next Steps

Fuse is currently in limited access mode. The smart contracts are deployed to Sepolia testnet and have been thoroughly tested. The frontend is complete and ready for users.

What's Working:

• ✅ All core smart contract functionality
• ✅ Full test coverage
• ✅ Premium frontend interface
• ✅ Real-time price monitoring
• ✅ Email invitation system

What's Next:

• 🔄 External security audit (before mainnet)
• 🔄 Chainlink Automation integration (for automated swaps)
• 🔄 Mainnet deployment (Avalanche C-Chain)
• 🔄 Additional features based on user feedback

The roadmap for Fuse - security first, then scale

Try It Yourself

If you're interested in trying Fuse, you can:

• Request Early Access - Visit fuse.aniketghavte.xyz and request an invitation
• Test on Sepolia - The contracts are live on Sepolia testnet
• Review the Code - All smart contracts are open source (coming soon)
• Read the Docs - Comprehensive documentation (coming soon)

The call-to-action section from the landing page

Final Thoughts

Building Fuse has been one of the most challenging and rewarding projects I've worked on. It combines everything I love about software development: solving real problems, writing secure code, creating beautiful interfaces, and learning constantly.

The DeFi space is still young, and there's so much room for innovation. Fuse is my contribution to making DeFi more accessible, safer, and easier to use. If you're a developer thinking about building in DeFi, my advice is: start small, test everything, and never stop learning.

If you have questions about Fuse, the architecture, or DeFi development in general, feel free to reach out. I'm always happy to chat about smart contracts, security, or building products that matter.

Want to stay updated? Follow @preonsHQ on X for updates on Fuse and other projects.

Built with ❤️ using Solidity, Next.js, and a lot of coffee.