# SignalDesk AI – Crossref DOI Lookup

> SignalDesk AI – Crossref DOI Lookup is a paid API for AI agents from x402-agent.kariguetoazul.workers.dev, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-12).

Fetches structured bibliographic metadata for a scholarly article given its DOI, sourced from the Crossref API

## Facts

- Endpoint: GET https://x402-agent.kariguetoazul.workers.dev/api/research/crossref-doi?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signaldesk-ai-crossref-doi-lookup-bf3544e0
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_nln9wLD5KH4uxsPGgjMFC

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 signaldesk-ai-crossref-doi-lookup-bf3544e0
```

Example prompt: Can you pull up the full metadata for the paper with DOI 10.1038/nphys1170 — I need the title, authors, year, publisher, and how many times it's been cited?

## When to prefer this

Use this endpoint when you need structured, evidence-backed bibliographic metadata for a known DOI — especially when you need citation counts, license terms, author lists, or publisher details from Crossref specifically. Prefer this over a generic web search when you need machine-readable, normalized scholarly metadata rather than a human-readable abstract page.

## Known failure modes

- Invalid or malformed DOI format (must match pattern ^10\.[0-9]{4,9}/\S+$) returns a validation error
- DOI not found in Crossref registry returns a 404 or empty result
- Crossref API upstream unavailability causes a timeout or 503
- Payment not completed (x402 payment required) results in a 402 response before data is returned
- Rate limit or quota exhaustion on free tier blocks requests

## How this service works

Evidence-backed autonomous AI jobs and paid data tools. Queue/D1/cron run outside the chat; free quotas and bounded execution apply.

## Output

A JSON object containing the DOI, canonical URL, article type, publication year, title, list of authors (given and family names), citation count, publisher name, license details (URL, start date, content version), and source provenance metadata including when the record was fetched and its expiry.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "doi"
     ],
     "properties": {
      "doi": {
       "type": "string",
       "pattern": "^10\\.[0-9]{4,9}/\\S+$",
       "maxLength": 250,
       "minLength": 6,
       "description": "DOI."
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "doi": "10.1038/nphys1170",
  "url": "https://doi.org/10.1038/nphys1170",
  "type": "journal-article",
  "year": 2009,
  "title": "Measured measurement",
  "source": {
   "provider": "Crossref metadata",
   "expires_at": "2026-10-03T09:44:49.169Z",
   "fetched_at": "2026-10-02T09:44:49.169Z",
   "source_url": "https://api.crossref.org/works/10.1038%2Fnphys1170",
   "transformed": true
  },
  "authors": [
   {
    "given": "Markus",
    "family": "Aspelmeyer"
   }
  ],
  "cited_by": 11,
  "licenses": [
   {
    "URL": "http://www.springer.com/tdm",
    "start": {
     "date-time": "2009-01-01T00:00:00Z",
     "timestamp": 1230768000000,
     "date-parts": [
      [
       2009,
       1,
       1
      ]
     ]
    },
    "delay-in-days": 0,
    "content-version": "tdm"
   }
  ],
  "publisher": "Springer Science and Business Media LLC"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signaldesk-ai-crossref-doi-lookup-bf3544e0/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-agent.kariguetoazul.workers.dev](https://www.zero.xyz/host/x402-agent.kariguetoazul.workers.dev/llms.txt)