Filed Open Tax Engine
opentax.filed.com - Fully open-source federal tax calculation engine. Single binary. Runs on macOS, Linux, and Windows.
Note: This engine calculates taxes accurately for use by AI agents and developers. For filing your taxes, visit irs.gov.
Built and maintained by AI agents using official IRS publications as the sole source of truth.
Covers Form 1040 (TY2025) today. Additional forms and state returns coming.
Why
- Professional tax calculation engines are closed source, expensive, and built for humans — making it hard for AI agents to reliably use one as a calculator
- AI agents have drastically reduced the cost of building and maintaining a tax engine. It only makes sense to do it in the open
- This project aims to be the first truly open-source, up-to-date tax calculation engine that works for everyone
Designed for the AI era:
- Built to be run by AI agents more than humans
- Single binary CLI that AI agents can download and run instantly
- Everything stored locally. Open, secure, and accessible
Inspired by Andrej Karpathy's autoresearch, an autonomous loop where AI agents modify code, measure results, and keep only improvements. OpenTax applies the same idea to tax calculation: agents read IRS instructions, write implementations, generate test cases, and fix regressions in a continuous loop.
Use with AI agents
Copy-paste this into Claude Desktop app:
Load the skill here using curl or equivalent:
https://raw.githubusercontent.com/filedcom/opentax/main/skills/opentax/SKILL.md
Then run the onboarding flow.
Claude Code
If you use Claude Code, install OpenTax as a plugin so the skill is always available:
- Add the marketplace:
/plugin marketplace add filedcom/opentax
- Install the plugin:
/plugin install opentax@opentax
- Use the skills:
/opentax:opentax # guided onboarding, picks the right skill for you
/opentax:tax-preparer # prepare a return from scratch
/opentax:tax-reviewer # audit a completed return against source docs
Install CLI
One command. No runtime, no installer, no dependencies.
curl -fsSL https://raw.githubusercontent.com/filedcom/opentax/main/install.sh | sh
- Detects your OS and architecture automatically
- Downloads the right binary and puts it in your PATH
Or download manually:
Example: single W-2 filer
$ opentax return create --year 2025
{ "returnId": "a1b2c3" }
$ opentax form add --returnId a1b2c3 --node_type general '{"filing_status": "single"}'
{ "id": "general_01", "nodeType": "general" }
$ opentax form add --returnId a1b2c3 --node_type w2 '{"box1_wages": 55000, "box2_fed_withheld": 5200}'
{ "id": "w2_01", "nodeType": "w2" }
$ opentax return get --returnId a1b2c3
{
"returnId": "a1b2c3",
"year": 2025,
"summary": {
"line1z_total_wages": 55000,
"line9_total_income": 55000,
"line11_agi": 55000,
"line15_taxable_income": 39250,
"line24_total_tax": 4471.5,
"line33_total_payments": 5200,
"line35a_refund": 728.5
},
"lines": {
"filing_status": "single",
"line1a_wages": 55000,
"line12a_standard_deduction": 15750,
"line15_taxable_income": 39250,
"line16_income_tax": 4471.5,
"line24_total_tax": 4471.5,
"line25a_w2_withheld": 5200,
"line33_total_payments": 5200,
"line34_overpayment": 728.5,
"line35a_refund": 728.5
}
}
$55,000 in wages, $15,750 standard deduction, $39,250 taxable income, $4,471.50 tax, $728.50 refund. Every line traces back to the IRS instructions.
More commands
# Validate against IRS MeF business rules
opentax return validate --returnId a1b2c3
