E-Notary on Monad Mainnet

What I Built I built Monad E-Notary, a decentralized, production-ready "Proof of Existence" dApp deployed on the Monad Mainnet (Chain ID: 143), with a mirrored staging version running on the Monad Testnet. The application allows users to securely stamp and verify the integrity of any PDF document. Using Solidity, I engineered the PDFNotary.sol smart contract to act as an immutable on-chain ledger. On the frontend, I utilized React, Vite, Tailwind CSS, and the Viem/Wagmi libraries to build a high-performance web interface. To manage metadata efficiently without sacrificing decentralization, I built a synchronized backend API and database layer that dynamically indexes transaction logs from both networks simultaneously. The Problems It Solves Traditional legal notarization is slow, expensive, and heavily centralized. My application solves three critical challenges: Document Fraud: Digital records are easily manipulated. By hashing files, my dApp creates an unalterable digital DNA string. Storing this hash on-chain provides absolute, time-stamped proof of a document's exact state at a specific moment. Data Privacy: Uploading confidential contracts to third-party servers risks leaks. My app uses local, client-side cryptographic hashing. The actual PDF never leaves the user’s device; only the mathematically irreversible hash is transmitted, ensuring 100% privacy by design. The Gas Barrier: Executing data-integrity contract calls on legacy blockchains is too costly for everyday use. By deploying on Monad, I leveraged hyper-optimized parallel execution to offer near-instant finality and micro-gas fees, making mass-scale digital notary services economically viable. What I Learned I isolated separate Testnet and Mainnet environments within a single codebase using strict environment variable sanitation. I faced and overcame a classic Web3 runtime debugging challenge where an accidental trailing space in a contract address string invalidated the checksum.