TaxMan is a very early prototype of a universal tax calculator API. It's running at http://taxman.openspending.org.

It provides a JSON API to find out tax rates for countries around the world, and to perform the relevant calculations to work out what tax citizens pay (and have paid in the past).

Get a list of jurisdictions currently supported by TaxMan:

$ curl -s 'taxman.openspending.org'
{
  "message": "Welcome to the TaxMan",
  "jurisdictions": {
    "gb": "http://taxman.openspending.org/gb"
  }
}

Get tax rates for the current year:

$ curl -s 'taxman.openspending.org/gb'
{
  "data": {
    "allowances": {
      "personal": 8105,
      "personal_income_limit": 25400
    },
    "income_tax": {
      "bands": [
        {
          "width": 34370,
          "rate": 0.2
        },
...

Get the UK personal allowance for 2002:

$ curl -s 'taxman.openspending.org/gb?year=2002' | json data.allowances.personal
4615

Find out how much income tax you would pay with a salary of £22,000:

$ curl -s 'taxman.openspending.org/gb?income=22000' | json calculation.income_tax.total
2779

And so on. Specify a callback GET parameter if you want JSONP back rather than JSON.

You can add a tax calculator for your own jurisdiction! Fork this repository and add a module for your jurisdiction, using the ISO 3166 two-letter code for your country as a name. For example, if you wanted to add taxes for Spain, you'd create tax/es/index.coffee, implementing the calculate() function:

exports.calculate = (params) ->
  # do your tax calculation...

  return {
    options: [parsed options]
    data: [raw data used to perform the tax calculation]
    calculation: [the tax calculation]
  }

At the moment we place no restrictions on what you return from the calculate function. That said, it is hoped that as we add more jurisdictions we will work out which parts of the API we can standardise. Consistency across jurisdictions is very important if TaxMan is to be useful, and at the moment we are relying entirely on contributors' discipline to ensure it.

To run the server locally, you'll need to have Node.js and npm installed. You can then run:

npm install .
`npm bin`/coffee serve.coffee