# Research Paper & DOI Lookup (Crossref)

> Research Paper & DOI Lookup (Crossref) is a paid API for AI agents from paper-lookup-production-56b0.up.railway.app, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-30).

Search or resolve scholarly publications using Crossref's 150M+ record database, returning metadata including authors, journal, citation count, and full-text links.

## Facts

- Endpoint: GET https://paper-lookup-production-56b0.up.railway.app/v1/papers/search?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/research-paper-doi-lookup-crossref-3ff811c4
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_cVoLCtW2jGXyHZbPt_tNm

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 research-paper-doi-lookup-crossref-3ff811c4
```

Example prompt: Can you look up the paper with DOI 10.1038/nature12373 and tell me the authors, journal, publication date, and how many times it's been cited?

## When to prefer this

Choose this endpoint when an agent needs to verify, look up, or search scholarly publications using Crossref's authoritative 150M+ record database. Ideal for DOI resolution, citation verification, author searches, and topic-based literature discovery with year and type filters. Prefer over Google Scholar scraping or PubMed when broad cross-domain coverage and structured metadata (ORCID, funders, licences, citation counts) are required.

## Known failure modes

- DOI not found in Crossref — returns empty results or error status
- Query returns zero results if keywords are too specific or misspelled
- Rate limiting or payment failure returns 402 Payment Required
- Invalid DOI format may return an error or empty match
- Some records may lack citation counts, ORCID, or full-text links if not registered with Crossref
- Abstracts are intentionally excluded from all results

## How this service works

Scholarly works metadata from Crossref (150M+ records): resolve a DOI, or search by keywords, author or title with year and type filters. Returns title, authors with ORCID, journal or publisher, publication date, type, ISSN/ISBN, citation count, references count, licence and full-text links, funders. Abstracts are excluded. Use when an agent must verify a citation or DOI, find papers on a topic, or get a paper's authors, journal, date, citation count and links.

## Output

Returns a JSON object with status, total result count, and an array of paper records each containing: DOI, canonical URL, publication type, title, authors (with ORCID where available), citation count, container (journal/publisher name), and publication date. Also includes legal/terms links and a use_when guidance field.

## 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",
     "properties": {
      "doi": {
       "type": "string",
       "description": "DOI to resolve, e.g. 10.1038/nature12373"
      },
      "type": {
       "type": "string",
       "description": "Crossref type, e.g. journal-article, book-chapter, posted-content"
      },
      "limit": {
       "type": "integer",
       "description": "Results 1-20 (default 10)"
      },
      "query": {
       "type": "string",
       "description": "Keywords (title, abstract words, topics)"
      },
      "author": {
       "type": "string",
       "description": "Author name filter"
      },
      "from_year": {
       "type": "integer",
       "description": "Earliest publication year"
      },
      "until_year": {
       "type": "integer",
       "description": "Latest publication year"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "legal": {
   "terms": "https://paper-lookup-production-56b0.up.railway.app/terms",
   "privacy": "https://paper-lookup-production-56b0.up.railway.app/privacy"
  },
  "total": 28674,
  "status": "ok",
  "results": [
   {
    "doi": "10.1016/j.watres.2018.05.060",
    "url": "https://doi.org/10.1016/j.watres.2018.05.060",
    "type": "journal-article",
    "title": "Microplastics in drinking water ...",
    "authors": [
     {
      "name": "A. Author",
      "orcid": null
     }
    ],
    "cited_by": 512,
    "container": "Water Research",
    "published": "2018-09-01"
   }
  ],
  "use_when": "Use when an agent must verify a citation or DOI, find papers on a topic, or get a paper's authors, journal, date, citation count and links."
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/research-paper-doi-lookup-crossref-3ff811c4/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from paper-lookup-production-56b0.up.railway.app](https://www.zero.xyz/host/paper-lookup-production-56b0.up.railway.app/llms.txt)