This set of Frequently Asked Questions (FAQ) provides answers to some commonly asked questions that may arise when using Library of Congress digital collections. If you have a question that you would like to have added and do not see represented here, please contact us via Ask a Librarian or email LC-Labs@loc.gov.
If you can see or hear the materials on the Library of Congress website, you may view or listen to them on the site. We are making them available to you for that very purpose. If you want to use or reuse the materials beyond our website, though, you need to be aware of copyright and other rights restrictions. (Just because we’ve put a work online doesn’t mean that you can freely reuse it.) You need to decide for yourself whether the way you plan to use the materials is allowed under copyright law.
API queries are subject to two types of limits: there is a limit to the rate at which the API will return information and a limit on how many results can be returned in a single search.
API rate limits depend on which collection you are attempting to access. Most collections are limited to a search burst of 80 requests per minute. If you exceed this limit, your access to the API will typically be blocked for an hour.
The current rate limits are:
Burst Limit - 20 requests per 1 minute, Block for 5 minutes
Crawl Limit - 20 requests per 10 seconds, Block for 1 hour
Item and resource endpoints
Burst Limit - 40 requests per 10 seconds, Block for 5 minutes
Crawl Limit - 200 requests per 1 minute, Block for 1 hour
Collections, format, and other endpoints
Burst Limit - 20 requests per 10 seconds, Block for 5 minutes
Crawl Limit - 80 requests per 1 minute, Block for 1 hour
Regardless of the rate at which results are returned, searches are limited to 100,000 results at a time.
Please visit the APIs for LoC.gov for more information.