# URL Reference Resolver (RFC 3986)

> URL Reference Resolver (RFC 3986) is a paid API for AI agents from url.openverbs.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).

Resolves a relative or absolute URL reference against an absolute base URL following RFC 3986 semantics

## Facts

- Endpoint: POST https://url.openverbs.com/v1/resolve
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/url-reference-resolver-rfc-3986-6cd1b378
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_4dZ-lFcJQSSAv01NE6uw2

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 url-reference-resolver-rfc-3986-6cd1b378 -d '<json body>'
```

Example prompt: I found the relative link '../images/photo.jpg' on the page 'https://example.com/blog/post/index.html' — can you resolve that to its full absolute URL?

## When to prefer this

Choose this endpoint when you need standards-compliant RFC 3986 reference resolution — especially for dot-segment paths like '../' or './', protocol-relative references like '//cdn.example.com/img.png', or any case where browser-like WHATWG URL resolution semantics are needed. It is ideal when building web crawlers, link extractors, sitemap generators, or redirect-chain resolvers that must correctly compute absolute URLs from relative hrefs found in HTML or HTTP headers.

## Known failure modes

- 400 error if base is not a valid absolute URL
- 400 error if inputs are malformed or missing required fields
- Malformed or oversized ref/base strings (exceeding 8192 characters) may be rejected
- Network timeout or 5xx if the service is temporarily unavailable

## How this service works

Resolve a relative or absolute reference against a base URL, following RFC 3986 reference resolution (e.g. base 'https://a.com/x/y' + ref '../z' → 'https://a.com/z'). The base must itself be a valid absolute URL, else a clean 400.

## Output

Returns the fully resolved absolute URL string computed by applying RFC 3986 reference resolution rules to the given base and reference. If the base is not a valid absolute URL, the endpoint returns a 400 error with a descriptive message.

## Request schema (JSON Schema)

```json
{
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "type": "object",
 "properties": {
  "input": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "type": "string",
     "enum": [
      "POST"
     ]
    },
    "bodyType": {
     "type": "string",
     "enum": [
      "json",
      "form-data",
      "text"
     ]
    },
    "body": {
     "type": "object",
     "properties": {
      "base": {
       "type": "string",
       "minLength": 1,
       "maxLength": 8192,
       "description": "The absolute base URL."
      },
      "ref": {
       "type": "string",
       "maxLength": 8192,
       "description": "The reference to resolve against the base."
      }
     },
     "required": [
      "base",
      "ref"
     ],
     "additionalProperties": false
    }
   },
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "additionalProperties": false
  }
 },
 "required": [
  "input"
 ]
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/url-reference-resolver-rfc-3986-6cd1b378/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from url.openverbs.com](https://www.zero.xyz/host/url.openverbs.com/llms.txt)