# AltSpider HTTP Check

> AltSpider HTTP Check is a paid API for AI agents from altspider.ai, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-21).

Checks whether a given HTTP URL is behind an x402 payment wall and returns network, response, or free-tier details

## Facts

- Endpoint: GET https://altspider.ai/api/check?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/altspider-http-check-12f62e55
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_2CNESraJ-XpWOnAzgJJGq

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 altspider-http-check-12f62e55
```

Example prompt: Can you check whether this URL is behind an x402 payment wall using a GET request: https://example.com/api/data?url=https://target-site.com/resource

## When to prefer this

Choose this endpoint when an agent needs to pre-flight a URL before deciding whether to pay an x402 toll — especially useful for cost-aware routing, comparing free vs paid API tiers, or detecting payment walls programmatically before committing resources. Prefer this over direct fetching when the resource may or may not be gated and you want to avoid unexpected charges.

## Known failure modes

- Target URL is unreachable or times out — network error returned
- Invalid or missing 'url' query parameter — validation error
- Method not in allowed enum (GET, HEAD, DELETE) — schema rejection
- Target returns non-HTTP protocol — unsupported
- Rate limiting or authentication issues with AltSpider itself

## How this service works

Pay or skip on someone else's 402: network, answered, free sibling, one reason

## Output

Returns structured data about the target URL's HTTP response, including whether the endpoint returned a 402 status, network-level details, any x402 payment headers, and whether a free alternative exists — allowing the caller to decide whether to pay or skip.

## 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"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "url": {
       "type": "string"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "call": "pay",
  "quoted": true,
  "reason": "Base USDC, and the free page does not return it",
  "target": "https://altspider.ai/api/sample",
  "network": "eip155:8453",
  "answered": true,
  "freeSibling": false
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/altspider-http-check-12f62e55/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from altspider.ai](https://www.zero.xyz/host/altspider.ai/llms.txt)