Making API Requests
How to craft a request to the JSON/YAML API for loc.gov
Content Covered by the loc.gov API
Most of the collections content on the loc.gov website is presented on parts of the website, called endpoints, that are implemented via the loc.gov API. There are a number of subsites on loc.gov that were not implemented with the loc.gov API and so do not provide API responses. A few examples of sites that do not provide loc.gov API response are:
- The National Library Service for the Blind and Print Disabled site at https://www.loc.gov/nls/
- The Publishers site at https://www.loc.gov/publish/
- The Cataloging and Acquisitions site at https://www.loc.gov/aba/
- Research room sites at https://www.loc.gov/rr/
- The American Folklife Center site at /research-centers/american-folklife-center/
- The Prints and Photographs Online Catalog site at https://www.loc.gov/pictures/
There are other parts of the website that are implemented using the API, such as the Library's events site and the Library's visitors site, but which do not provide simple search or item responses and are not discussed in the following documentation.
Base URL
The API response underlying any page displayed may be exposed by adding an API response
format parameter,
?fo=json, to the end of any loc.gov page that is implemented using the API. Requests
to the JSON/YAML API use the base url
https://www.loc.gov/{endpoint}/?fo=json. To return data in YAML format, simply change
fo=jsonto
fo=yaml.
The base url can be adjusted by changing the
endpoint and/or adding
parameters to the
query string, i.e. the portion of the url following a
? A query string uses
query parameters to narrow search results. Multiple parameters, also
known as
key value pairs, can be used in the same query string and are conjoined
by an
&, e.g.
https://www.loc.gov/photos/?fa=location:washington+d.c.&q=bridges&fo=json.
An explanation of the search endpoints (/search, /{format}, /collections, and /collections/{collection}) and the item / resource endpoints (/item, /resource) follows in the API Endpoints documentation. An explanation of some of the query parameters available with the API follows in the API Parameters documentation.