Tax is public law. Its software should be too.
Tax work happens in a company's tax department and in a tax authority. This site maps that work team by team, lists every open source project that does part of it, shows where nothing open exists yet, and teaches tax people how to build what is missing. No licence fees. No black boxes. No lock-in.
- Step 1The mapWhere tax work happens and by whom: a company's tax department and a tax authority, 19 teams and 35 activities, each marked covered, partly covered or gap.
- Step 2ProjectsEvery open source tax project, 733 today, placed on the map and searchable by tax, country and kind.
- Step 3The gaps3 activities with no open project and 23 partly covered, each with what to build on and where to start.
- Step 4Learn to buildHow engines, agents and MCP servers work, with a route for your role, so you can build for a gap.
Where open source already does tax work. And where it doesn't yet.
A company's tax department and a tax authority, drawn team by team: 19 teams and 35 activities. Every activity is marked covered, partly covered or gap, and opens its own page.
Company tax department19 activities · 2 covered · 12 partly covered · 3 gaps
Tax authority16 activities · 4 covered · 11 partly covered · 0 gaps
298 entries joined the list in Oct 2026. Every one with a page of its own.
The list holds 733 open source tax projects, each placed on the map where it fits. Browse them by tax area, by jurisdiction or by kind, or search the whole list.
- Automations82 new
- APIs70 new
- Tax datasets68 new
- Tax engines28 new
- Calculators27 new
- MCP8 new
- Models7 new
- Agent skills4 new
- Benchmarks4 new
10 to start with.
A first cut of the projects already out there. Some are run by governments, some by researchers, some by a single stubborn maintainer. The open slot is an invitation.
3 activities with no open project. Pick one and build it.
Each runs on published rules or a standard schema. On the Gaps page, every gap says what to build on, what a first version could do, and which track on Learn helps, and the 23 partly covered activities say what is open and what is still missing.
Written for fiscalists, not engineers.
Your judgement is the scarce part. Learn how open engines, agents and protocols work, so you can make that judgement run at scale — without handing it to a vendor.
- 01
Rules as code
Read how OpenFisca and Direct File turn statute into logic you can test, diff and review.
- 02
Agents and skills
Package your expertise as an agent skill: the steps, the sources, the checks — in plain language.
- 03
MCP and APIs
Connect agents to legislation, case law and your own ledgers through open protocols.
- 04
Evidence and review
Benchmarks, source citation, and the four-eyes review no model replaces.
--- name: eu-vat-reverse-charge description: Checks whether a cross-border B2B service falls under the EU reverse charge, and cites the provision it relies on. --- # Steps 1. Confirm supplier and customer are both taxable persons. 2. Validate the customer's VAT number via VIES. 3. Apply the general B2B place-of-supply rule — Art. 44, Directive 2006/112/EC 4. If it applies, the customer accounts for VAT — Art. 196 5. Cite every article. Flag exceptions for human review.
A tax system runs on trust, and trust needs checking.
Read the manifesto