Isocast

Isocast — Polymarket Weather-Signal API for AI Agents

API at https://api.isocast.dev. Isocast watches 37 cities and, when a city's observed daily-high temperature crosses out of one Polymarket temperature bucket and into another, emits exactly one signal for that (city, day, transition). Every signal carries the Polymarket market URL, the old and new {reading, unit, bucket}, and live YES/NO/midpoint odds for every bucket (with dead: true on buckets the day can no longer reach). Browsing is free and needs no auth; deeper signals are per-city bundles bought pay-per-call.

Full API docs: api.isocast.dev/llms.txt | OpenAPI spec: api.isocast.dev/openapi.json

What a signal is

A signal fires when a city's daily-high reading moves into a new Polymarket bucket. It includes the market URL, the old/new bucket readings, and current odds for every bucket, plus bucketsAsOf (odds freshness, ~10s) and observedAt. Delivery is at-most-once per (city, day, bucket), and seq is a monotonic per-city counter so you can track what you've seen.

Free endpoints (no auth, no payment)

Every JSON response also carries a disclaimer string.

Quick Start — Browse a City (free)

// All free, no auth, no setup
const BASE = "https://api.isocast.dev";

// 1. List active cities
const cities = await (await fetch(`${BASE}/v1/cities`)).json();
// cities: [{ slug, unit, bucketWidth, timezone, latestSeq }, ...]

// 2. Inspect today's market for one city
const city = await (await fetch(`${BASE}/v1/cities/istanbul`)).json();
// city: { slug, targetDate, marketUrl, ... }

// 3. See a sample signal shape before paying
const sample = await (await fetch(`${BASE}/v1/sample?city=istanbul`)).json();
// sample.signal: { marketUrl, old, new, buckets, observedAt, ... }, sample: true

Paid signals

The cheapest read is GET /v1/spot?city=SLUG — a $0.01 snapshot of the city's latest signal, payable by a STOCK x402 client (plain @x402/fetch wrapFetchWithPayment, no custom nonce). For a running feed, buy a prepaid per-city bundle via /v1/subscribe (pay-per-call via x402; the effective unit price drops with bundle size), then read /v1/signals. Agents can use the isocast-mcp npm package (an MCP server) which handles payment for you, or read the full flow at api.isocast.dev/llms.txt. Entitled signals can also be pushed to a Telegram chat (free — the delivery registration route never charges).

Error Handling

• 402 — Payment required for a paid signal route. See the docs above for the payment flow.
• 429 — Rate limited. Respect the Retry-After header (seconds to wait).
• 404 — Unknown or inactive city.

Machine discovery

Disclaimer

Informational data only — not financial or betting advice. No guarantee of accuracy or outcome; prediction markets are restricted in some jurisdictions. Terms: https://isocast.dev/terms