As of June 2019, FPbase is moving to a GraphQL-based API. GraphQL is a modern query language that gives clients the power to ask for exactly what (fields) they need and nothing more, and makes it easier to evolve APIs over time.
The new entrypoint is: https://www.fpbase.org/graphql/
If you visit the entrypoint in a browser, you will be met with the GraphiQL IDE for exploring the FPbase schema. Use the documentation explorer on the right to see what queries are available, and test out various queries in the pane on the left. For instance: get the name and sequence of every protein in the database
You may POST queries to the entrypoint to retrieve data in JSON format.
For more information on how to query in GraphQL, see the official documentation.
FPbase has a REST API for retrieving data in JSON or CSV format. It is very basic and still in development (unstable). Until we know there are people who would like to use it, there are a lot of other things that also need attention. So let us know if you'd like to use it!
NOTE: FPbase is moving away from the REST API, and all development will use the GraphQL API mentioned above.