MultiSendr

MultiSendr is a DeFi app that lets users swap or send many stablecoins in a single transaction. It runs on the Avail blockchain. The goal is to save gas, reduce steps, and make cross-chain stablecoin transfers easy.

Problem we solve

1. Users must do one swap or transfer per transaction. This costs more gas and takes more time.
2. Sending stablecoins to many recipients or across chains is slow and error-prone.
3. Developers lack a simple UI for batching stablecoin operations on Substrate-based chains.

Our solution

We let users create one batched operation that performs many stablecoin swaps or sends at once. The platform executes that batch on Avail. Users see live rates and real-time transaction status. This reduces cost, complexity and time.

Key features

1. Batch stablecoin swaps in one transaction.
2. Batch sending to multiple recipients in one transaction.
3. Cross-chain support for common stablecoins (USDC, USDT, DAI).
4. Real-time exchange rates via CoinGecko.
5. Polkadot.js wallet support (Polkadot.js extension, Talisman, SubWallet).
6. Live transaction tracking using WebSocket from Avail.
7. Gas optimizations through batching.
8. Safety features: reentrancy guard, owner controls, emergency pause.

How it works (step-by-step)

1. User connects a wallet (Polkadot.js or other supported).
2. User prepares a batch: either a list of swaps or a list of transfers.
3. UI fetches live exchange rates and shows expected outputs.
4. User reviews fees and signs the single batched transaction.
5. The signed transaction is sent to Avail.
6. App listens for status updates and shows success or failure.
7. On success, balances update and transaction details are shown.

Demo & UX

1. Clean, simple UI.
2. Form to build batch (add swap entries or recipient addresses).
3. Preview for totals, fees, and slippage.
4. Big confirm button that signs one transaction.
5. Live logs and transaction receipt once mined.

Why Avail?

Avail gives modular data availability and low fees. It fits batch and cross-chain logic well. It is built for high throughput and works nicely with Polkadot.js tools.

What’s next (roadmap)

1. Add more stablecoins and bridges.
2. On-ramp / off-ramp for fiat.
3. Mobile UI and wallet integrations.
4. Analytics dashboard for batch performance and gas savings.
5. Community features like referrals and rewards.

Impact

MultiSendr saves users time and money. It makes stablecoin transfers and swaps simpler. It opens a path for batch financial flows on Substrate-based chains.

We built MultiSendr using Avail SDK and the Polkadot.js API to handle blockchain communication and transaction execution. The goal was to make it possible to swap or send multiple stablecoins in one single transaction instead of many separate ones.

On the frontend, we used Next.js, React, and Tailwind CSS to create a clean and responsive interface. The app connects directly to the user’s Polkadot.js wallet, allowing them to sign and send transactions easily.

For the backend logic, we created an AvailService in TypeScript that connects to the Avail Turing testnet using WebSocket (wss://turing-rpc.avail.so/ws). This service handles wallet connections, transaction creation, signing, and sending. We also used CoinGecko’s API to fetch real-time stablecoin prices so users always see up-to-date exchange rates.

The smart contract layer is split into two parts:

1. A Solidity contract for EVM-based testing and to simulate swaps across chains.

2. A Rust (ink!) contract for native deployment on Avail, handling token balances, rates, and batch swap logic directly inside the Substrate runtime.

We used Hardhat for deploying Solidity contracts and ContractPromise (Polkadot.js) for deploying the ink! contract. Balances, rates, and transaction statuses are all updated live through WebSocket connections to the Avail node.

One particularly hacky and fun part was optimizing the batch transaction builder. We had to make sure multiple swaps or transfers were combined into one valid transaction object before signing which saved a lot of gas and network calls.

The Polkadot.js extension made integration easier, giving users a secure and familiar wallet connection while letting us focus on building the batch logic and real-time experience.

In short, MultiSendr brings together React + Avail SDK + Polkadot.js + ink! smart contracts into one smooth pipeline — from wallet connection to transaction confirmation — all designed for speed, simplicity, and cost efficiency.