# SiteSignal Crossref DOI Metadata

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

Returns bounded bibliographic, authorship, publication, subject, funding, license, and citation-count metadata for a single DOI from Crossref.

## Facts

- Endpoint: GET https://trinity-throw-thursday-gravity.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-12b7b55b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Zie2CYtvY3n26NjD6XEjr

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-12b7b55b
```

Example prompt: Can you pull up the full bibliographic details for DOI 10.1038/nature12373 — I need the authors, journal, publication date, citation count, and license information?

## When to prefer this

Use this endpoint when you need structured, authoritative bibliographic metadata for a known DOI from Crossref's database, particularly when citation counts, funding details, and license terms are required alongside standard bibliographic fields. Prefer this over scraping publisher pages or using general web search when you need machine-readable, normalized metadata for academic literature workflows.

## Known failure modes

- DOI not found in Crossref — returns empty or error response
- Malformed DOI string (too short, invalid prefix) — rejected by input validation
- DOI exists but metadata is sparse (common for older articles) — partial fields returned
- Crossref API downtime or rate limiting — upstream timeout or error
- Payment failure — endpoint requires $0.01 USDC x402 payment before serving response

## How this service works

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

## Output

A structured record containing bibliographic metadata (title, authors, abstract), publication details (journal, publisher, volume, issue, page numbers, publication date), subject/category classifications, funding acknowledgements, license terms, and the Crossref 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-12b7b55b/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from trinity-throw-thursday-gravity.trycloudflare.com](https://www.zero.xyz/host/trinity-throw-thursday-gravity.trycloudflare.com/llms.txt)