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OpenFisca Legislation explorer

A web user interface to explore an OpenFisca tax and benefit system.

This application consumes a legislation description made available by the OpenFisca web API and makes its parameters and formulas searchable and interlinked. Example.

Development stack

This application is based on Node on the backend and React on the frontend.

In order to run the server or to improve the app, first install Node and NPM and Git. Then, run the following commands:

git clone
cd legislation-explorer
npm install --production

Configure your instance

You will need to tell the Legislation Explorer server where your OpenFisca API instance can be reached, as well as where your repository resides for contributors to be directed to. This is all done through environment variables, allowing you to use the same code for any instance by injecting these elements at runtime.

To set these options, you need to define them by prefixing the npm start or npm run dev commands with their definitions, in the $NAME=$VALUE syntax.

  • API_URL: the URL at which your OpenFisca API root endpoint can be found. For example: Defaults to
  • CHANGELOG_URL: the URL at which the changelog for the country package can be found. Used on 404 pages. For example:

If it gets lengthy or you want to persist these values, you can also use a .env file. Such a file is a plaintext file with name .env stored in the root directory of your legislation explorer instance (i.e. next to the package.json file). List all of your environment variables in the $NAME=$VALUE syntax, one per line. If you have trouble writing this file, read the parsing rules. An example file is provided as .env.example, setting default values. You can copy it, but changing it won't have any impact: only a file named .env will be taken into account. You should not commit this file: it depends on each instance.

Localisation (l12n / i18n)

The user interface of the legislation explorer has full support for internationalisation. Supported languages can be found in the src/assets/lang directory, and can be added by simply creating a new file with the two-letter language code to add support for.

For localisation, you can override any of the strings defined in these files through the UI_STRINGS environment variable.

  • UI_STRINGS: overrides the ui config object through a JSON string. Example: UI_STRINGS='{"en":{"countryName":"Tunisia"},"fr":{"countryName":"Tunisie"}}' npm start.

The value is a JSON-encoded object whose keys are ISO two-letters language codes and values are strings, these values will take precedence over any strings defined in the lang folder.

The following strings are strongly recommended to be overridden:

  • countryName: The name of the tax and benefit system you are modelling here.
    • forCountry: In case the default interpolation for your countryName does not give good results, you can also edit the prefix added before the countryName value.
  • search_placeholder: One or two suggested searches, preferably comma-separated, for your users to make sense of the search field. Best results will be obtained by using the most well-known parameters for your tax and benefit system.


This web app supports Matomo (ex-Piwik) analytics out of the box. To set it up, use the following environment variables:

  • MATOMO_URL: the base URL at which the Matomo instance can be reached. For example: MATOMO_URL= MATOMO_SITE_ID=4 npm start. Only taken into account if used in conjunction with MATOMO_SITE_ID and if MATOMO_CONFIG is not defined.
  • MATOMO_SITE_ID: The ID of the site to track in this Matomo instance. For example: MATOMO_URL= MATOMO_SITE_ID=4 npm start. Only taken into account if used in conjunction with MATOMO_URL and if MATOMO_CONFIG is not defined.
  • MATOMO_CONFIG: a JSON-encoded object describing how to contact your Matomo instance. The value is a configuration object for the piwik-react-router package (make sure to read its docs for the version specified in package.json). Defaults to not sending analytics at all. Example: 'MATOMO_CONFIG='{"url":"","siteId":4}' npm start.

Server and public URL

  • PATHNAME defines the path at which the Legislation Explorer is served. Defaults to /. For example: PATHNAME=/legislation to serve on
  • HOST: defines the host on which the app is served. Example: HOST= npm start. Defaults to (all local interfaces).
  • PORT defines the port on which the app is served. Example: PORT=80 npm start. Defaults to 2020.

Development-specific options

  • NODE_ENV defines if assets should be served minified or with hot module remplacement. Can be either development or production. Example: NODE_ENV=production PORT=2020 node index.js. Prefer using npm start.

Run the server

cd to the cloned legislation-explorer directory, and run the following commands:

npm run build  # compile the frontend code
npm start  # start the server

Improve the app

You can edit all files in the source folder you cloned. In order to ease development, a different set of commands will allow you to run the app with hot module replacement, which will reflect your changes almost instantly rather than rebuilding the whole package.

cd to the cloned legislation-explorer directory, and run the following commands:

npm install  # install development dependencies
npm run dev

Some additional commands can be useful for development. You can discover all of them by running npm run.


This app has both unit and integration tests. Its integration tests are implemented with Watai. You will first need to install its Selenium WebDriver dependencies to run these tests.

Then, build the app, run the server, run a Selenium instance and, in another Terminal, run:

npm run test