# SiteSignal Crossref DOI Metadata

> SiteSignal Crossref DOI Metadata is a paid API for AI agents from phases-prot-shine-royal.trycloudflare.com, paid per call via x402, $0.01/call, status down (last checked 2026-09-15).

Returns bibliographic, authorship, publication, subject, funding, license, and citation-count metadata for a given DOI via the Crossref registry.

## Facts

- Endpoint: GET https://phases-prot-shine-royal.trycloudflare.com/x402/doi-metadata
- Price: $0.01/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/sitesignal-crossref-doi-metadata-d4f96735
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_b7IwMSwNhVCEj9aRia4n_

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 sitesignal-crossref-doi-metadata-d4f96735
```

Example prompt: Can you pull the full bibliographic metadata for DOI 10.1038/s41586-021-03819-2, including authors, journal, publication date, citation count, and funding info?

## When to prefer this

Choose this endpoint when you need structured, authoritative bibliographic metadata for a specific scholarly DOI, including citation counts, funding, licensing, and authorship — sourced directly from the Crossref registry. Prefer this over general web scraping or other DOI resolvers when you need machine-readable, normalized academic metadata rather than a rendered landing page.

## Known failure modes

- DOI not found in Crossref registry — returns empty or error response
- Malformed DOI string (e.g. includes full doi.org URL prefix instead of bare DOI) — rejected by schema validation
- Crossref rate limiting or upstream downtime — may return timeout or 5xx error
- DOI exists but has incomplete metadata — some fields may be null or absent
- Non-scholarly DOIs (e.g. for datasets or grey literature) may have sparse metadata

## How this service works

Return bounded bibliographic, authorship, publication, subject, funding, license, and citation-count metadata for one DOI from Crossref.

## Output

A structured JSON object containing bounded bibliographic metadata from Crossref, including: title, authors, publication venue, publication date, subject classifications, funding acknowledgements, license information, and citation count for the requested DOI.

## 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": [
      "doi"
     ],
     "properties": {
      "doi": {
       "type": "string",
       "maxLength": 255,
       "minLength": 7,
       "description": "Bare DOI without a doi.org resolver URL."
      }
     }
    }
   },
   "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/sitesignal-crossref-doi-metadata-d4f96735/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from phases-prot-shine-royal.trycloudflare.com](https://www.zero.xyz/host/phases-prot-shine-royal.trycloudflare.com/llms.txt)