Cachemarket

An on-chain data caching protocol built on Monad. The first requester seeds the cache and pays full price; every subsequent requester reads from on-chain storage for 100x less. No API keys, no subscriptions — just a wallet.

Built for Monad Blitz Denver 2025

Cachemarket was built in one day on February 17, 2025 at Monad Blitz Denver, a hackathon challenging developers to build consumer dApps on the Monad blockchain. We wanted to prove a simple idea: what if paying for data was built directly into HTTP, and the first person to ask a question could subsidize everyone who asks after them?

The result is a data freshness marketplace that uses the x402 payment protocol (HTTP 402 Payment Required) to let anyone — humans or AI agents — query real-world data (crypto prices, weather, country info) and pay per request on-chain. The first requester seeds the cache for 0.001 MON. Everyone else reads it for 0.0001 MON. After 60 seconds the data expires and the cycle restarts.

How it works

1. You ask a natural language question ("price of ETH", "weather in Denver", "Japan info")
2. The gateway checks the DataCache smart contract on Monad for a cached answer
3. Cache hit — you pay 0.0001 MON and get the data instantly
4. Cache miss — you pay 0.001 MON, the gateway fetches fresh data from an external API, stores it on-chain, and returns it to you
5. The data lives on-chain for 60 seconds. During that window, every subsequent reader pays 100x less
6. After the TTL expires, the next requester becomes the new seeder

User / Agent
     │
     ▼  POST /api/query (no payment header)
  Gateway  ──────►  402 Payment Required { price, payTo, chainId }
     │
     ▼  Send MON to payTo
  Gateway  ──────►  Verify tx on-chain
     │
     ├── Cache HIT  → return cached data (0.0001 MON)
     └── Cache MISS → fetch from API → store on Monad → return fresh data (0.001 MON)

Data sources

Category	API	Example queries
Crypto prices	CoinGecko	"ETH price", "price of bitcoin", "SOL"
Weather	wttr.in	"Denver weather", "weather in Paris"
Country info	REST Countries	"France info", "Japan country"
AI fallback	Groq (Llama 3.3 70B)	Any other question (optional)

Setup

1. Install dependencies:

   yarn install

2. Copy the environment file and fill in your values:

   cp packages/nextjs/.env.example packages/nextjs/.env.local

3. Edit .env.local with:

   • NEXT_PUBLIC_SERVER_WALLET — Wallet address that receives payments
   • BACKEND_PRIVATE_KEY — Private key for signing storeResult() transactions
   • DATACACHE_ADDRESS — Deployed DataCache contract address (see packages/foundry/deployments/10143.json)
   • NEXT_PUBLIC_WALLET_CONNECT_PROJECT_ID — WalletConnect project ID

4. Start the app:

   yarn start

   Visit http://localhost:3000

Using the CLI

cd cli
cp .env.example .env
# fill in PRIVATE_KEY
npm install
npm run build

cachemarket query "price of ETH"
cachemarket stats

Using the SDK

import { CacheMarket } from "@cachemarket/sdk";

const client = new CacheMarket({
  privateKey: "0x...",
  rpcUrl: "https://testnet-rpc.monad.xyz",
});

// Read from cache (free)
const { isCached, data } = await client.checkCache("ETH price");

// Full query (cache check → fetch if miss → store on-chain)
const result = await client.query("weather in Denver");

Smart contract

DataCache is deployed on Monad Testnet (chain ID 10143).

Function	Description
checkCache(bytes32 queryHash)	Returns whether data is cached and not expired
storeResult(bytes32, string, string, address)	Stores fresh data on-chain with a 60s TTL
getResult(bytes32 queryHash)	Returns data, seeder address, timestamp, and hit count
getStats()	Returns total seeds, cache hits, and queries

Source: packages/foundry/contracts/DataCache.sol

Technology stack

Layer	Technology
Frontend	Next.js 15, React, Tailwind CSS, Framer Motion
Wallet	RainbowKit, wagmi, viem
Smart contracts	Solidity, Foundry
Blockchain	Monad Testnet (EVM-compatible, 10,000 TPS, sub-second finality)
Payment protocol	x402 (HTTP 402 Payment Required)
Backend (alt)	Hono.js
External APIs	CoinGecko, wttr.in, REST Countries, Groq

Project structure

cachemarket/
├── packages/
│   ├── nextjs/          # Main app (frontend + API routes)
│   └── foundry/         # Solidity contracts + Foundry tooling
├── backend/             # Standalone Hono.js gateway (port 4402)
├── cli/                 # CLI tool — cachemarket query "..."
├── sdk/                 # TypeScript SDK — @cachemarket/sdk
└── docs/                # Full technical reference

For the full technical reference (component docs, hook internals, navigation logic, state management), see docs/TECHNICAL_REFERENCE.md.

The problem Cachemarket solves

Every API call today requires authentication, rate limits, and subscriptions. AI agents can't pay for data programmatically. Developers manage dozens of API keys across services. And when two people ask the same question seconds apart, the same data gets fetched twice.

Cachemarket removes all of that. One on-chain contract, one payment rail, zero API keys. The first person to ask pays for fresh data and stores it on Monad. Everyone who asks the same question within 60 seconds reads from on-chain storage at 1/100th the cost. The cache key is a keccak256 hash of the normalized query, so identical questions always resolve to the same entry.

Built on Monad's sub-second finality and sub-cent transaction costs, micropayments are practical for the first time — paying 0.0001 MON per cached read is economically viable because the chain makes it so.

Why Monad

• 10,000 TPS with optimistic parallel execution — handles high query throughput without congestion
• Sub-second finality (0.8s) — payments confirm before the user notices
• Sub-cent fees — micropayments for cached reads are economically viable
• Full EVM compatibility — Solidity, viem, wagmi, Foundry all work with zero changes

Team

Built by three students from DeVinci Blockchain (Paris, France) at Monad Blitz Denver, February 17, 2025.

Name	Role	Links
Sofiane Ben Taleb	Full-Stack & Smart Contracts	GitHub · LinkedIn
Armand Sechon	Backend & Infrastructure	GitHub · LinkedIn
Noe Wales	Frontend & Design	GitHub · LinkedIn