11 open source tax projects for Netherlands.

Every project on the list for Netherlands, grouped by kind. Global tools have a page of their own. Entries without a warning come first in each group; the labels mark what to check.

11 projects10 maintained7 on the map21 jurisdictions + globalFacts checked 6 Oct 2026

Browse these by tax area

Income tax Corporate tax Benefits VAT & indirect Cross-cutting

Tax engines

3 projects

Rules-as-code that compute liabilities, returns and reforms.

ALEF (Belastingdienst)Dutch Tax Administration tool for writing executable tax rules in RegelSpraak without programming.Tax engineNL

OpenFisca NLEarly OpenFisca model of Dutch tax and benefit rules.Tax engineNL

tax-treaty-agentRule-engine pre-review of China's treaties with NL, SG and KR for dividends, interest and royalties.Tax engineCN · NL · SG · KRDemo

Calculators

2 projects

Small tools that compute one tax for one country.

Dutch Tax Income CalculatorAngular web calculator for Dutch income tax; the rules sit in a separate npm package.CalculatorNLFor individual taxpayers

motorrijtuigenbelastingTypeScript SDK and CLI that calculate Dutch motor vehicle tax from vehicle data and RDW lookups.CalculatorNLInactive since 2024For individual taxpayers

Plugins

1 project

Bundles of skills, tools and agents, installable in one go.

NL Tax Agent SkillsPlugin that turns Dutch tax documents into workpacks for manual entry in Mijn Belastingdienst.PluginNLFor individual taxpayers

APIs

2 projects

Validation, rates, filings and registries you can call directly.

Dutch Peppol Authority validationSchematron and XSL validation artefacts for SI-UBL and NLCIUS e-invoices from the Dutch Peppol Authority.APINL

ubl-peppolPHP library that builds UBL 2.1 e-invoices for Peppol BIS Billing 3.0.APIEU · NL · BE

Automations

2 projects

Reusable workflows for provisions, reconciliations and compliance runs.

OCA l10n-netherlands (Odoo)Odoo modules for the Dutch VAT return, the ICP listing and the XAF audit file.AutomationNL

OpenBooksEarly-stage accounting app with EU VAT logic, invoicing and Peppol export.AutomationEU · NL

Tax datasets

1 project

Rates, treaties and statistics, open and versioned.

myTransferPricing referenceSummaries of 18 OECD transfer pricing country profiles, with a prompt that reviews a Local File against one.Tax datasetAT · BE · BR · DK · FR · DE · GR · IE · IT · LU · NL · PL · SG · ES · SE · CH · UK · US

Labels mark what to check before you rely on an entry: inactive or archived code, demos, paid services and unclear licences. Only maintained projects for companies and tax authorities appear on the map. Search and filter the whole list.

Missing a project? Add it to the list.

Submit a project

Next · Step 3 of 4The gapsThe activities with no open project yet, and the partly covered ones, with what to build on.