A crypto lending and borrowing app. Put money in to earn interest, or keep your ETH and borrow cash against it.
This is a pet project. I am learning Solidity properly, so instead of writing a few toy contracts I am building one full product the way a real team would — smart contracts, tests, a backend, a web app, deployment scripts and documentation.
| Document | Who it is for |
|---|---|
| How it works | Anyone. What the app does, what you can do with it, and the one risk borrowers must understand. No prior knowledge assumed |
| Running the system | Anyone who wants to try it. From an empty machine to lending, borrowing and liquidating on a local chain, including MetaMask setup |
| User guide | Anyone using the app. Every screen and every term explained in detail |
| Architecture | Anyone reading the code. How the three pieces fit together and why |
| Setup | Anyone building from source. Tooling, tests, and the regeneration step |
| API reference | Anyone building against the backend. Every endpoint, with request and response shapes |
Start with running the system if you want to see it work. It is the only document that takes you from nothing to a working setup you can click through.
| Part | State |
|---|---|
| Smart contracts | Done. 7 contracts, 282 tests passing, including fuzz and invariant suites |
| Deployment scripts | Done. Deploys to a local chain with test positions ready to play with |
| Backend | All endpoints live and reading real data |
| Indexer | Reads contract events into Postgres, survives restarts, revalues positions on a timer |
| Web app | All 16 screens reading live data from the chain and the database |
| Signing transactions | Wired. Deposit, withdraw, borrow, repay, add and remove collateral, and liquidate |
Every figure on every screen is read from the chain or from indexed blockchain history. There is no placeholder data left in the app.
- Three of the six signing flows are unverified end to end. Collateral deposits and liquidation have been confirmed on-chain; borrow, repay and lend have not
- The reorg rollback path has never run. It is written and it deletes rows, which makes it the least proven code in the repository
- No market snapshots, so there are no historical trends to show
- A liquidator gets no transaction of their own — their side is recorded on the settlement, not in their history
- No tests on the web app, and the indexer has tests only for event decoding
- One market only — lock ETH, borrow USDC. No other coins
- No insurance fund, so a very sudden crash can still leave bad debt
- No upgrades — fixing a contract means deploying a new one
- Nobody has audited this. It is a learning project, not somewhere to put real money
contracts/ Solidity — the rules. The only part that can move money
backend/ Go — indexes the blockchain and serves history and totals quickly
frontend/ Next.js — the screens people use
abi/ The shared description of the contracts, generated from the Solidity
docs/ The documents linked above
One rule shapes all of it: the contracts decide, everything else only displays. The backend and the web app can be wrong and the worst that happens is a confusing number on a screen. If a contract is wrong, money is lost.
Four commands, assuming Foundry, Docker and Node are installed:
anvil --host 0.0.0.0 # terminal 1
cd contracts && forge script script/SeedLocal.s.sol \
--tc SeedLocal --rpc-url http://localhost:8545 --broadcast # terminal 2
cd backend && cp .env.example .env && docker compose up -d # terminal 3
cd frontend && npm install && npm run dev # terminal 4The database tables and MetaMask still need setting up. Running the system covers both, and explains what the seed script creates.