# Polymarket Top Markets by Topic

> Polymarket Top Markets by Topic is a paid API for AI agents from x402-datashop-production.up.railway.app, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).

Returns top open Polymarket prediction markets for a given topic tag, ranked by 24-hour volume, with event titles, end dates, and outcome probabilities.

## Facts

- Endpoint: GET https://x402-datashop-production.up.railway.app/v1/predict/polymarket
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/polymarket-top-markets-by-topic-2a51bd38
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Zdnc-WyZAcTeNlZqCni9N

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability polymarket-top-markets-by-topic-2a51bd38
```

Example prompt: What are the top 5 Polymarket prediction markets for politics right now, including the current odds for each outcome?

## When to prefer this

Use this endpoint when you need live, ranked prediction market odds from Polymarket for a specific topic category. Prefer this over general news or sentiment APIs when you want crowd-sourced probabilistic forecasts backed by real on-chain USD volume. Best for crypto, politics, economics, and Fed-related forecasting questions.

## Known failure modes

- Invalid or unrecognized tag slug returns empty results or 404
- limit out of range (< 1 or > 10) returns a validation error
- Polymarket Gamma API unavailable causes upstream 502/503
- Payment not included or insufficient USDC results in 402 Payment Required
- Stale data possible within the 5-minute cache window

## How this service works

Top open Polymarket prediction markets for a topic, ranked by 24h volume: event title, end date, and per-market outcome probabilities (0-1) with USD volume, from the public Gamma API (live on-chain odds). Query: ?tag=crypto|politics|economy|fed|... (any Polymarket tag slug) &limit=1-10 (default crypto, 5). JSON, 5min cache.

## Output

A JSON array of up to 10 open Polymarket events for the requested tag, each containing: event title, end date, and a list of outcomes with their current probability (0-1) and 24-hour USD trading volume. Results are cached for 5 minutes and ranked by 24h volume.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "tag": {
       "type": "string",
       "default": "crypto",
       "description": "Polymarket tag slug, e.g. crypto, politics, economy"
      },
      "limit": {
       "type": "integer",
       "default": 5,
       "maximum": 10,
       "minimum": 1,
       "description": "Events to return"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/polymarket-top-markets-by-topic-2a51bd38/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-datashop-production.up.railway.app](https://www.zero.xyz/host/x402-datashop-production.up.railway.app/llms.txt)