Welcome to crossref’s documentation!
Contents:
The Crossref API is a RESTful API based on HTTP and JSON. It is designed to be friendly and helpful. It is also rate limited to ensure fair usage.
The Crossref API is organized around [DOIs](https://www.doi.org/). DOIs are persistent identifiers for scholarly content on the internet. They take the form of a prefix and a suffix separated by a slash. The prefix is assigned to a publisher by [Crossref](https://www.crossref.org/). The suffix is created by the publisher and must be unique for each item they publish. The Crossref API allows you to retrieve metadata for a DOI as well as perform full text search and faceted queries.
The Crossref API is a [Hypermedia API](https://en.wikipedia.org/wiki/Hypermedia). This means that it is designed to be browsed with a web browser. You can use a web browser to explore the API and discover new resources. The API is also designed to be consumed by machines. You can use a programming language like Python or Ruby to write programs that interact with the API.
Rate Limits
The Crossref API is rate limited to ensure fair usage. The rate limit is 50 requests per second. If you exceed this rate you will receive a 503 response code. If you receive a 503 or 429 response code you should back off and retry after a few seconds.
Authentication
The Crossref API does not require authentication. You can make requests to the API without providing any credentials. However, if you are making a large number of requests to the API you should consider using an API key. You can obtain an API key by registering for a Crossref account at https://crossref.org/. You can then pass your API key as a query parameter with each request to the API. For example: