Filed Open Tax Engine CLI
An open US federal tax engine in a single binary: a CLI and Claude Code skills that prepare and review Form 1040 returns.
- 134 ★ on the repository
- Last commit
- AGPL-3.0
Extended access
Why this level
- Handles tax data and personal identifiers; the result does not replace a professional.
Install
- Works in
Manual install
/plugin marketplace add filedcom/opentaxThe first plugin install step for Claude Code in the README, followed by `/plugin install opentax@opentax`. The CLI installs separately via the repository `install.sh` script.
Access and checks
How we reviewExtended accessThe tool runs code or makes network calls and only reads external data.
- Handles tax data and personal identifiers; the result does not replace a professional.
This is third-party code. Review the repository files before installing.
What it does
OpenTax calculates US federal income tax from official IRS publications. The engine is a graph of nodes, each taking validated input and returning typed output. It currently covers Form 1040 for 2025 with 195 input types (W-2, 1099, schedules, deductions), while Form 1040 and the Form 4868 extension are started for 2026. `opentax return create`, `form add`, `return get` and `return validate` create a return, add documents and check IRS rules locally. Export goes to MeF XML, a filled PDF or a submission package. In Claude Code the plugin adds `/opentax:opentax` for onboarding, `/opentax:tax-preparer` for preparation and `/opentax:tax-reviewer` for auditing a finished return.
Who it is for. Developers and US taxpayers who want an agent to compute a return on an open engine instead of inventing numbers.
Good fit when
- An agent must compute Form 1040 tax from W-2 and 1099 data.
- A finished return needs checking against source documents.
- You need offline IRS MeF business rule validation without sending data.
- A developer embeds tax calculation in their own agent service.
Not a fit when
- You need IRS filing; a clean validation is not IRS acceptance.
- You need state or non-US taxes; only the US federal return is covered.
- You want tax advice; the tool calculates but gives none.
Example request
Create a 2025 return, add a W-2 with wages of 55000 and 5200 withheld, then show the line summary and warnings.Limitations
Form 1040 for 2025 is covered. For 2026 the engine refuses inputs whose rules are not yet added. A clean validation does not mean IRS acceptance, and export needs the filer personal data, including the social security number. Data stays on disk in `./.state/returns`, but uploading documents to a hosted assistant discloses them to that provider. The engine and skills are maintained by AI agents and do not replace a tax professional. The license is AGPL-3.0.
How to disable. In Claude Code run `/plugin uninstall opentax@opentax` and delete the `opentax` binary from PATH. Remove local returns in `./.state/returns` by hand.
FAQ
Which tax forms are supported?
Form 1040 for 2025 with 195 input types. For 2026 Form 1040 (`general`, `w2`, `f8888`) and Form 4868 are started.
Does the tool file the return with the IRS?
No, it calculates, validates and exports files. Filing needs your own EFIN and Software ID, and a clean validation is not IRS acceptance.
Where is data stored?
Locally in `./.state/returns`. Uploading source documents to a hosted assistant discloses them to that provider.
How do I check the result?
Run `opentax return validate --returnId <id>`: it runs IRS MeF business rules locally. Warnings also appear in `return get` output.
How do I update?
Run `opentax update`. The engine reports when a new version is available.
Discussion
No questions or reviews yet.
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README in short
The engine is checked on 137 benchmark cases for 2025 with values compared against cited IRS publications. AI agents maintain the code: they read IRS instructions and write calculation nodes.