All the documentation about API usage can be found on the API documentation page, but here is a quick summary:

-  The Open Food Facts database is available as open data under the Open Database License (ODbL), see https://world.openfoodfacts.org/terms-of-use for the legal details. The two conditions are attribution and share-alike. If you combine data from Open Food Facts with other databases, then the ODbL requires that the resulting database must be released as open data as well. It also means that you can combine the data only with sources that would allow such redistribution.

- You must always use a custom User-Agent when performing API calls to identify your app.

- Rate-limits are enforced for each API endpoint.