OpenFisca provides a web API package, compatible with all country packages. Using a web interface, app developers can access information and computations without installing anything locally.
The latest version of the OpenFisca Country Template web API can be found at api.demo.openfisca.org. Its endpoints are documented at legislation.demo.openfisca.org/swagger.
Each country/jurisdiction can host an API endpoint and often an OpenFisca instance is deployed multiple times in support of different applications. By way of example, an instance of the French API is available at api.fr.openfisca.org. It is provided for prototyping purposes only: it has no SLA (service level agreement, i.e. guarantee of availability) and is kept up to date automatically, with no regard for breaking changes. No support is provided for this instance. You should not build production systems against it.
Anyone wanting a stable OpenFisca web API is invited to host their own.
Visit https://openfisca.org/en/showcase/ to browse a wide variety of use cases.
Please remember that OpenFisca is free software, licensed under an Affero GPL licence. That means you have to provide access to the source code of the API you make available, including any changes you might have made to the original code. You also have to provide a link to the OpenFisca source code, and state its licence, in a place that is easily discoverable by users of your software.
You could for example add one the following lines to a “credits” page:
Computations done by <a href="https://openfisca.org">OpenFisca</a>, the <a href="https://choosealicense.com/licenses/agpl-3.0/" title="AGPL-3.0">free and open-source</a> social and fiscal computation engine. Source code available at <a href="https://github.com/openfisca">github.com/openfisca</a>.
Calculs effectués par <a href="https://openfisca.org">OpenFisca</a>, le moteur <a href="https://choosealicense.com/licenses/agpl-3.0/" title="AGPL-3.0">libre et ouvert</a> du système social et fiscal. Code source disponible sur <a href="https://github.com/openfisca">github.com/openfisca</a>.
Let app developers access your country package information and computations by serving the web API that comes bundled with the OpenFisca-Core module. See the technical documentation for serving instructions.
If you want to track how your API is being used, you can install the OpenFisca Tracker.