# Polygon PoS Checkpoint Fetcher

> Polygon PoS Checkpoint Fetcher is a paid API for AI agents from api.chainmarket-api.workers.dev, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-24).

Returns the latest Polygon PoS (Heimdall) checkpoints including block ranges, proposers, timestamps, and inter-checkpoint timing statistics.

## Facts

- Endpoint: GET https://api.chainmarket-api.workers.dev/api/crypto/polygon-pos-checkpoints?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-24
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/polygon-pos-checkpoint-fetcher-57a39a2d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_iVOcsCEj1uuwQI1D3Smiq

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 polygon-pos-checkpoint-fetcher-57a39a2d
```

Example prompt: What are the last 5 Polygon PoS checkpoints — give me the block ranges, proposers, and how long on average between them?

## When to prefer this

Use this endpoint when you need real-time Polygon PoS checkpoint data sourced directly from Polygon's official Heimdall API, especially for finality monitoring, validator/proposer tracking, bridge readiness checks, or cross-chain state verification — without needing an API key or account. Prefer it over raw RPC calls when you want pre-parsed, structured checkpoint metadata with timing statistics in a single pay-per-call request.

## Known failure modes

- Invalid count parameter (outside 1–10 range) may return an error or default behavior
- Upstream Heimdall API unavailability causing fetch failure
- Stale data if the upstream Polygon Heimdall API is lagging
- Network timeout from the Cloudflare Worker to the upstream source

## How this service works

Polygon PoS checkpoints from the Heimdall API: the latest K checkpoints (1 to 10) with their Bor block range, timestamp and proposer, plus the average spacing in blocks and seconds. Checkpoints are the Ethereum-anchored root commitments. State-sync logs are not included.

## Output

A JSON object containing the requested number of latest Polygon PoS checkpoints (default 3, max 10), each with checkpoint ID, start block, end block, proposer address, timestamp, block count, and Bor chain ID, plus aggregate statistics: average blocks between checkpoints and average seconds between checkpoints. Also includes the source URL and the time the data was fetched.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "count": {
       "type": "string",
       "description": "How many latest checkpoints, 1 to 10 (default 3)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "count": 3,
  "source": "https://heimdall-api.polygon.technology/checkpoints/latest",
  "checkedAt": "2026-10-23T09:36:01.084Z",
  "checkpoints": [
   {
    "id": 114911,
    "endBlock": 96027301,
    "proposer": "0x203847fbc212987f83680e0682e45e930eb11b0e",
    "timestamp": "2026-10-23T09:23:36.000Z",
    "blockCount": 1536,
    "borChainId": "137",
    "startBlock": 96025766
   },
   {
    "id": 114910,
    "endBlock": 96025765,
    "proposer": "0x02f70172f7f490653665c9bfac0666147c8af1f5",
    "timestamp": "2026-10-23T08:43:56.000Z",
    "blockCount": 512,
    "borChainId": "137",
    "startBlock": 96025254
   }
  ],
  "avgBlocksBetween": 1024,
  "avgSecondsBetween": 1600.5
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/polygon-pos-checkpoint-fetcher-57a39a2d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.chainmarket-api.workers.dev](https://www.zero.xyz/host/api.chainmarket-api.workers.dev/llms.txt)