Build for a gap

Step 2 of 4 · ProjectsBy kind

All projects By kind Tax engines

Tax engines: 74 open source projects.

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

74 projects58 maintained45 on the map28 jurisdictions + globalFacts checked 6 Oct 2026

Browse these by tax area

Income tax Corporate tax Benefits Payroll tax VAT & indirect Cross-cutting

accounting-harnessDeterministic accounting and audit harness with an ASC 740 module for the current and deferred provision.Tax engineUS

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

CatalaProgramming language for writing law as code, next to the legal text it implements.Tax engineGlobal · FR

CIT24AI-assisted Thai corporate income tax provision and compliance platform, from ledgers to filings.Tax engineTHLicence unknown

Cost-of-Capital-CalculatorCalculates the cost of capital and effective tax rates on new investment.Tax engineUS

DGFiP calculette-irThe M-language rules of the DGFiP engine that computes French income tax and the real-estate wealth tax (IFI).Tax engineFR

EUROMODThe EU tax-benefit microsimulation model, maintained by the Joint Research Centre.Tax engineEU

GETTSIMThe German Taxes and Transfers Simulator: a microsimulation model of German taxes and benefits.Tax engineDE

IRS Fact GraphKnowledge-graph rules engine that models the US Internal Revenue Code, the calculation core of Direct File.Tax engineUS

IRS Form BuilderScala library that turns flow XML, fact dictionaries and locale files into questionnaire sites on Fact Graph.Tax engineUS

MlangCompiler for DGFiP's M language, used to compute the income tax of French taxpayers.Tax engineFR

OG-CoreOverlapping-generations model framework for evaluating the economic effects of fiscal policy.Tax engineGlobal · US

OpenFileFree tax filing tool built on the published code of IRS Direct File.Tax engineUSFor individual taxpayersLicence unknown

OpenFiscaRules-as-code framework: legislation written in Python, served as a web API.Tax engineFR · Global

OpenFisca ArgentinaEarly OpenFisca model of Argentina's tax and benefit system.Tax engineAR

OpenFisca AustriaEarly OpenFisca model of Austria's tax and benefit system.Tax engineAT

OpenFisca CzechiaEarly OpenFisca model of the Czech tax and benefit system.Tax engineCZ

OpenFisca FranceThe French tax and benefit system, written as OpenFisca rules.Tax engineFR

OpenFisca France EntreprisesMicrosimulation of French firms' taxes and subsidies around the carbon tax, built on OpenFisca.Tax engineFR

OpenFisca France indirect taxationOpenFisca model of French indirect taxes.Tax engineFR

OpenFisca IndiaEarly OpenFisca model of India's tax and benefit system.Tax engineIN

OpenFisca JapanJapan's tax and benefit rules as an OpenFisca API, with a web app on top.Tax engineJP

OpenFisca KoreaEarly OpenFisca model of South Korea's tax and benefit rules.Tax engineKR

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

OpenFisca Nouvelle-CalédonieNew Caledonia's tax and benefit system for OpenFisca.Tax engineNC

OpenFisca ParaguayParaguay's tax and benefit system for OpenFisca.Tax enginePY

OpenFisca Polynésie françaiseFrench Polynesia's tax system as OpenFisca rules-as-code.Tax enginePF

OpenFisca SenegalSenegal's tax and benefit system for OpenFisca.Tax engineSN

OpenFisca TunisiaTunisia's tax and benefit system for OpenFisca.Tax engineTNLicence unknown

openscheduleSouth African SARS customs tariff schedule tooling for versioned, auditable rule sets.Tax engineZA

OpenTaxUS federal tax engine as a single binary CLI built for AI agents; covers Form 1040 for 2025.Tax engineUSFor individual taxpayers

OpenTax EngineDeterministic US federal and state tax engine for AI agents with proof trees for each result.Tax engineUS

PolicyEngineOpen tax-benefit models with a public app for scoring policy reforms.Tax engineUS · UK

PolicyEngine AustraliaMicrosimulation model of Australia's tax and benefit system.Tax engineAULicence unknown

PolicyEngine CanadaModel of Canada's tax and benefit system, built on PolicyEngine Core.Tax engineCA

PolicyEngine CoreCore microsimulation engine for PolicyEngine models, forked from OpenFisca Core.Tax engineGlobal

PolicyEngine TAXSIMTAXSIM emulator built on PolicyEngine's US federal and state tax calculator.Tax engineUS

PolicyEngine UKOpen-source static tax-benefit microsimulation model for the UK.Tax engineUK

PolicyEngine USRules engine and microsimulation model of the US tax-benefit system.Tax engineUS

policyengine.pyPolicyEngine's Python package that brings the country models, analysis and charts together.Tax engineGlobal

section382Section 382 and 383 loss limitation engine: ownership-change analyser, annual limitation, anti-abuse rules.Tax engineUSLicence unknown

Skatteetaten trekktabellJava routine from the Norwegian Tax Administration that computes withholding tax from the tax tables.Tax engineNOLicence unknown

tariff-engineRule-based HS classification engine (AI at build time, deterministic at runtime) covering 20 chapters; on npm.Tax engineGlobal

Tax-CalculatorFederal income and payroll tax microsimulation from the Policy Simulation Library.Tax engineUS

tax-logic-coreJavaScript library for US federal and state tax calculations, with IRS citations.Tax engineUSFor individual taxpayers

tax-mindChinese tax risk assessment and compliance decision support: Golden Tax IV rules, four-flow matching, reports.Tax engineCN

tenfortyPython package that computes US federal and state income tax and is built on Open Tax Solver.Tax engineUSFor individual taxpayers

UK land value taxDashboard that models replacing UK council tax with a land value tax.Tax engineUKLicence unknown

UK VATLabToolkit for modelling UK VAT policy.Tax engineUKLicence unknown

UsTaxesFree web and desktop app to prepare US federal 1040 returns with data kept on the user's computer.Tax engineUSFor individual taxpayers

AfCFTA_Rules_of_OriginRust prototype encoding the AfCFTA rules of origin (Article 5) as rules-as-data.Tax engineGlobalDemo

Agent-Based Simulation of International Tax ComplianceNetLogo model of how a foreign tax system's spillover changes domestic tax evasion and avoidance.Tax engineGlobalInactive since 2021

borderlogix-hs-engineFastAPI implementing WCO GIR 1 to 6 for Papua New Guinea customs classification with duty and SAD mapping.Tax enginePGDemoNeeds a paid serviceLicence unknown

canataxLightweight Canadian sales and income tax calculator.Tax engineCAInactive since 2025

catala-explainModule that explains a Catala program's result from its execution trace.Tax engineFRInactive since 2023

customs-duty-calculator (ShahinHasanov90)Customs duty and tax engine (ad valorem, specific, compound and FTA rates) as a .NET 8 API.Tax engineGlobalDemo

customs-valuation-engineWCO six-method customs valuation engine in TypeScript with Incoterm adjustments and an audit trail.Tax engineGlobalDemoLicence unknown

DGFiP CAPROMASCAPROMAS, the Java calculator DGFiP uses for corporate income tax on the IS balance return (form 2572).Tax engineFRInactive since 2020

DGFiP CFECalculation code for the CFE, the property component of France's territorial economic contribution.Tax engineFRInactive since 2022Licence unknown

DGFiP CVAECalculation code for the CVAE, France's business value-added contribution.Tax engineFRInactive since 2021

DGFiP IFERCalculation code for the IFER flat-rate tax on energy, rail and telecom network companies.Tax engineFRInactive since 2022

DGFiP ir-catalaProof of concept of the French income tax calculation written in Catala, not used in production.Tax engineFRInactive since 2024Demo

DGFiP taxe d'habitationSource code and description of the French residence tax (taxe d'habitation) calculation.Tax engineFRInactive since 2024

DGFiP taxe foncièreSource code and description of the French property tax (taxe foncière) calculation.Tax engineFRInactive since 2024

fiscalize (grunt-it)Engine for EU national e-invoicing and fiscal clearance on EN 16931 with country adapters; a Slovenian pilot.Tax engineSI · EUDemoLicence unknown

HMRC CT calculationsScala library for UK Corporation Tax return boxes and CT600 computations, including CT600A and CT600J.Tax engineUKArchived

IRS Direct FileThe IRS filing tool. Shut down for 2026, but its code, Fact Graph included, is public.Tax engineUSArchivedDiscontinued · code public

OpenFisca AotearoaNew Zealand's legislation, regulation and policy as OpenFisca rules-as-code.Tax engineNZInactive since 2025

OpenFisca Canada (DTS)Experiment using OpenFisca as a rules engine for Canadian legislation, a jumping-off point for further work.Tax engineCAInactive since 2021Licence unknown

OpenFisca France inheritanceOpenFisca model of French inheritance tax rules.Tax engineFRInactive since 2025

PolicyEngine LegislationBuilderStreamlit app drafting legislation text from PolicyEngine reform code or plain-English prompts, using OpenAI.Tax engineGlobalNeeds a paid serviceLicence unknown

Scsl.Math.CustomsCode library for customs valuation and duty and VAT computation under Philippine regulations.Tax enginePHInactive since 2025

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

taxpro-ukUK FRS 102 corporate tax provision system: AI prepares, a deterministic engine calculates, people approve.Tax engineUKNeeds a paid service

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.

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