# Polymarket–Kalshi Arbitrage Spread Finder

> Polymarket–Kalshi Arbitrage Spread Finder is a paid API for AI agents from x402.agentutility.ai, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-14).

Finds arbitrage opportunities by cross-referencing matching prediction market questions on Polymarket and Kalshi and surfacing probability spreads between them.

## Facts

- Endpoint: POST https://x402.agentutility.ai/polymarket-kalshi-arbitrage
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/polymarket-kalshi-arbitrage-spread-finder-2648f7f0
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_LJ3luwjii4DPhwSe5ob-w

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-kalshi-arbitrage-spread-finder-2648f7f0 -d '<json body>'
```

Example prompt: Can you scan Polymarket and Kalshi right now and show me which matched prediction market questions have the biggest probability spread between the two platforms — I want to find arbitrage opportunities.

## When to prefer this

Use this endpoint when you need a real-time, cross-platform comparison of prediction market probabilities specifically between Polymarket and Kalshi. Prefer this over manually querying each platform's API when you want pre-matched pairs with spread calculations already computed and ready to act on.

## Known failure modes

- Kalshi or Polymarket API unavailable — empty pairs list or partial results
- No matching questions found above threshold — returns empty pairs array
- Payment not received — x402 payment required error before data is returned
- Low match_score pairs only — semantic matching may miss non-obvious equivalents

## How this service works

Paid x402 endpoints organized into product clusters. USDC-settled on Base. MCP-callable. ERC-8004 identity registry agentId 47167.

## Output

Returns a list of matched question pairs found across both platforms, each with a match score, the yes-probability on each platform, the spread value, the spread direction (e.g. polymarket_higher), and both platforms' question titles. Also includes the total pair count and data attribution.

## 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",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "properties": {
      "category": {
       "type": "string",
       "description": "Optional Polymarket category filter (substring)."
      },
      "min_spread": {
       "type": "number",
       "description": "Minimum |p_poly - p_kalshi| spread to report. 0-1. Default 0.05."
      },
      "scan_limit": {
       "type": "number",
       "description": "Max markets to pull from each venue. 10-500. Default 100."
      },
      "min_match_score": {
       "type": "number",
       "description": "Minimum Jaccard token overlap to treat two titles as the same event. 0-1. Default 0.4."
      }
     }
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "pairs": {
       "type": "array",
       "items": {
        "type": "object",
        "properties": {
         "spread": {
          "type": "number"
         },
         "match_score": {
          "type": "number"
         },
         "kalshi_title": {
          "type": "string"
         },
         "poly_question": {
          "type": "string"
         },
         "poly_yes_prob": {
          "type": "number"
         },
         "kalshi_yes_prob": {
          "type": "number"
         },
         "spread_direction": {
          "type": "string"
         }
        }
       }
      },
      "pair_count": {
       "type": "integer"
      },
      "attribution": {
       "type": "string"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "pairs": [
   {
    "spread": 0.07,
    "match_score": 0.5,
    "kalshi_title": "Will X win the presidential election?",
    "poly_question": "Will X win the election?",
    "poly_yes_prob": 0.62,
    "kalshi_yes_prob": 0.55,
    "spread_direction": "polymarket_higher"
   }
  ],
  "pair_count": 1,
  "attribution": "Data: Polymarket gamma-api + Kalshi public API."
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/polymarket-kalshi-arbitrage-spread-finder-2648f7f0/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.agentutility.ai](https://www.zero.xyz/host/x402.agentutility.ai/llms.txt)