DEV Community

pmestre-Forge
pmestre-Forge

Posted on

I Built a Pay-Per-Call Trading Signal API for AI Agents

#ai #crypto #python #webdev

If you're building AI agents that trade, they need market signals. But most data APIs require human signup, API keys, and monthly subscriptions — none of which an autonomous agent can handle.

I built a trading signal API where AI agents pay per call using the x402 protocol (USDC micropayments on Base L2). No signup, no API keys. Agent shows up, pays half a cent, gets data.

How x402 Works

x402 revives the HTTP 402 ("Payment Required") status code:

  1. Agent calls GET /signal/NVDA
  2. Server responds with HTTP 402 + payment instructions
  3. Agent wallet signs a USDC transfer on Base L2
  4. Agent retries with a payment proof header
  5. Server verifies via Coinbase facilitator, returns data

The entire flow takes ~200ms.

The Signal Engine

Each call returns a composite momentum score built from:

  • RSI (14) — oversold/overbought detection
  • ADX (14) — trend strength (>25 = strong trend)
  • MACD (12/26/9) — crossover + direction
  • Volume ratio — current vs 20-day average

Score maps to BUY (>=30), SELL (<=-30), or HOLD, with a confidence value from 0 to 1.

Endpoints

Endpoint Price Returns
/signal/TICKER $0.005 Single stock signal
/scan/momentum $0.01 Top 10 momentum setups
/risk?tickers=X,Y $0.01 Portfolio risk analysis

Stack

  • FastAPI (sync endpoints for yfinance blocking I/O)
  • x402 Python SDK with ASGI middleware
  • LRU cache (200 entries, 5-min TTL)
  • Deployed on Fly.io

Open source: https://github.com/pmestre-Forge/signal-api

If you're thinking about building services for the emerging AI agent economy, this is a template you can fork and adapt.

Top comments (0)