Documentation

Learn how to integrate CitationAPI into your application. Generate perfectly formatted citations from any URL with a single API call.

Base URL

https://api.citationapi.com

All endpoints require HTTPS

Getting Started

Get up and running in under a minute.

Sign up

Create a free account at citationapi.com/signup

Copy your API key

Find it on your dashboard after signing in.

Make a request

Use the example below to cite your first URL.

cURL

curl -X POST https://api.citationapi.com/v1/citations \
  -H "Content-Type: application/json" \
  -H "X-API-Key: ca_live_your_key_here" \
  -d '{"url": "https://doi.org/10.1038/s41586-020-2649-2"}'

Authentication

Authenticate requests with an API key.

All API requests require an API key passed in the X-API-Key header. You can create and manage API keys from your dashboard.

Header

X-API-Key: ca_live_your_key_here

Note: Requests without a valid API key will receive a 401 Unauthorized response. Sign up for a free account to get your API key.

Endpoints

Create and retrieve citations.

POST/v1/citations

Create a citation from a URL. Returns structured CSL-JSON metadata and pre-formatted citations.

Request Body

Parameter	Type	Status	Description
`url`	string	Required	The URL to generate a citation for.
`style`	string	Optional	Any CSL style ID (e.g. `apa`, `mla`, `chicago`, `ieee`, `vancouver`, and 9,000+ more). Omit to return all default styles (APA, MLA, Chicago, BibTeX).
`force`	boolean	Optional	Bypass cache and re-extract. Default: false.

Example Request

JSON

{
  "url": "https://doi.org/10.1038/s41586-020-2649-2",
  "style": "apa",
  "force": false
}

Response

JSON

{
  "id": "a1b2c3d4e5f6...",
  "url": "https://doi.org/10.1038/s41586-020-2649-2",
  "source": "crossref",
  "confidence": 0.98,
  "csl": {
    "type": "article-journal",
    "title": "Array programming with NumPy",
    "author": [
      {"family": "Harris", "given": "Charles R."},
      {"family": "Millman", "given": "K. Jarrod"}
    ],
    "issued": {"date-parts": [[2020, 9, 16]]},
    "container-title": "Nature",
    "volume": "585",
    "issue": "7825",
    "page": "357-362",
    "DOI": "10.1038/s41586-020-2649-2"
  },
  "formatted": {
    "apa": "Harris, C. R., Millman, K. J., ... (2020). Array programming with NumPy. Nature, 585(7825), 357–362.",
    "mla": "Harris, Charles R., et al. \"Array Programming with NumPy.\" Nature, vol. 585, ...",
    "chicago": "Harris, Charles R., K. Jarrod Millman, ... 2020. \"Array Programming with NumPy.\" ...",
    "bibtex": "@article{harris2020array, ...}"
  },
  "cached": false,
  "extracted_at": "2025-02-10T14:30:00Z"
}

GET/v1/citations/:id

Retrieve a previously extracted citation by its hash ID. Returns the same response format as the POST endpoint.

Path Parameters

Parameter	Type	Status	Description
`id`	string	Required	The SHA256 hash ID returned from the POST endpoint.

Rate Limits

Limits vary by plan and are applied per API key.

Plan	Rate Limit	Monthly Requests
Free	`10 req/min`	500
Developer	`60 req/min`	50,000
Pro	`300 req/min`	500,000

When rate limited, the API returns 429 Too Many Requests. Cached responses do not count against your extraction quota.

Error Codes

Standard HTTP error codes with descriptive messages.

Code	Meaning	Description
`400`	Bad Request	Missing or invalid URL in request body
`401`	Unauthorized	Invalid or missing API key
`404`	Not Found	Citation ID not found in cache
`422`	Unprocessable	URL is valid but could not be cited (extraction failed across all layers)
`429`	Rate Limited	Too many requests — slow down or upgrade plan
`500`	Server Error	Internal error — retry with exponential backoff

CSL-JSON Schema

The canonical data format for citation metadata.

CitationAPI uses CSL-JSON (Citation Style Language JSON) as its canonical data format. This is the same schema used by Zotero, Mendeley, and other reference managers.

Key Fields

Field	Type	Description
`type`	string	CSL type: "article-journal", "book", "software", "post", etc.
`title`	string	Title of the work
`author`	array	Array of name objects with "family" and "given" or "literal" keys
`issued`	object	Publication date as date-parts array
`container-title`	string	Journal name, book title, or repository
`DOI`	string	Digital Object Identifier
`URL`	string	Source URL of the work

Example Object

JSON

{
  "type": "article-journal",
  "title": "Array programming with NumPy",
  "author": [
    {"family": "Smith", "given": "John"},
    {"literal": "Organization Name"}
  ],
  "issued": {
    "date-parts": [[2024, 3, 15]]
  },
  "container-title": "Nature",
  "volume": "585",
  "issue": "7825",
  "page": "357-362",
  "DOI": "10.1038/s41586-020-2649-2",
  "URL": "https://example.com",
  "abstract": "..."
}

The csl field in every API response contains the full CSL-JSON object. You can use this with any CSL-compatible tool to render citations in custom styles.

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