Inspiration
AI agents can increasingly browse, book, and buy for users, but giving an agent spending power creates a serious trust problem. Existing AI wallets either expose too much money or don’t work with normal Web2 merchants. We wanted a middle path: let users express what they want in natural language, but keep every purchase constrained and human-approved.
What it does
MandatePay turns natural-language purchase requests into enforceable payment mandates.
Example request:
"Find me the cheapest Nike running shoes under S$120."
The agent then:
- Extracts product, budget, quantity, and preferences.
- Searches for qualifying products.
- Selects the best qualifying option.
- Funds a task-specific disposable virtual card using a stablecoin rail.
- Prepares checkout.
- Waits for explicit user approval before completing the purchase.
Core security model:
One agent task → one constrained disposable payment instrument → one checkout.
The user does not give the agent unrestricted access to funds. The blockchain provides the funding/settlement rail, while the disposable card provides compatibility with existing Web2 merchants.
How we built it
Our prototype architecture includes:
- Intent layer: LLM-powered agent for extracting purchase constraints and asking clarifying questions when needed.
- Discovery layer: Web2 product search and best-option selection.
- Payment layer: Stablecoin-funded disposable virtual card for merchant compatibility.
- Approval layer: Human-in-the-loop confirmation UI.
- Settlement layer: On-chain payment verification and funding.
Planned stack: Python, TypeScript, Next.js, LangChain/OpenAI, Solidity, Ethereum/Polygon, stablecoin rail, Playwright for checkout automation.
Challenges we faced
- Designing a mandate model that is simple enough for an MVP but secure enough to be meaningful.
- Bridging on-chain stablecoin funding with Web2 merchant checkout.
- Ensuring the agent cannot spend beyond the task-specific card.
- Keeping human approval meaningful without adding unnecessary friction.
What's next
- Real virtual card issuer integration.
- On-chain escrow and settlement proofs.
- Recurring or multi-step purchase mandates.
- Richer policy constraints for more complex user intents.
Built With
- contracts
- css
- ethereum
- ethers.js
- fastapi
- hardhat
- langchain
- next.js
- node.js
- openai
- playwright
- polygon
- postgresql
- python
- react
- smart
- solidity
- stablecoin
- supabase
- tailwind
- typescript
- vercel
- viem
- web3
Log in or sign up for Devpost to join the conversation.