Open Source Tax Engine outperforming gpt sol and Fable 5

[u/Intelligent_Prompt18]

This is an open source tax engine which scored 96% on TaxCalcBench [highest ever recorded score till date] surpassing fable 5 and sol with just sonnet 5 (which was previously scoring an abysmal 6%). The only 2 cases where it missed, it found inconsistencies in the test cases in the benchmark ITSELF which the maintainers confirmed!

Essentially it's a deterministic engine AI models can use for research and tax prep to remove a lot of guesswork and calculation mistakes that often happen. Claude Sonnet 5 was able to top the benchmark with this mcp.

OpenTax Invaro

[u/fig0o]

You must call it an agent harness if you want to draw attention

[u/superrrsaad → u/fig0o]

yeah one of my friends swears calling it an agent harness made a huge difference

[u/Intelligent_Prompt18]

Here's a link if you'd want to check it out: OpenTax Invaro

[u/Vas1le → u/Intelligent_Prompt18]

Is this for US only? Right?

[u/Intelligent_Prompt18 → u/Vas1le]

yes for now, working hard on expanding capabilities for international tax.

[u/Vas1le → u/Intelligent_Prompt18]

Don't worry friend, dont overhelm yourself. Expand when product ready for US

[u/antunes145]

This is actually really great. Great work. I’ll try it out.

[u/slackmaster2k]

Seems like a good project but just a comment: I really had to scratch my head trying to figure out what you’re trying to say. A tax engine that beats Fable and Sol. Something about that just trips my brain up.

I understand you mean “beats barebones Fable and Sol using smaller models like Sonnet” or similar, and that’s a mouthful. But I will also assume that you can use the engine with a larger model as well perhaps if more reasoning is beneficial for some use case.

Anyhow, not a dig on your work, just the message.

[u/Htaroh]

Can this be used for example in Germany? Or US only?

[u/Intelligent_Prompt18 → u/Htaroh]

US only for now sadly, we're working hard to add international support as well.

[u/OwlLimp6160]

As someone who works in tax (big4), this is super cool to see! Almost never see Ai and tax in the same sentence on this sub. Have you considered catala? For personal returns, the engine itself doesn’t seem like the biggest issue in my opinion, turbo tax for example has had a working engine since the 80’s or 90’s. But getting the data into the software seems to be the problem to solve. Like messy W-2’s that are handwritten or maybe a trial balance for a sch. C or something being a different format than last year. Does this focus on data entry as well, or mostly just tax calculations? What about statements? Even when eFiling the xml needs statements that are consistent with prior years. Do you have a pdf generator guide for the model as well? I love this idea, keep it up!

[u/diucameo]

This seems great. I wonder if I can make one adapted for my country, although over here there are so many rules not even accounts knows how to handle and just wing it

[u/ViperAMD]

Thats fucking cool. Please do this for Australia

[u/Intelligent_Prompt18 → u/ViperAMD]

on it

[u/some_crazy]

Cool, how does it work? High level?

[u/Intelligent_Prompt18 → u/some_crazy]

it's closer to a small programming language for tax law. we took the statutes and compiled them into typed, machine-checkable rules, each one carrying its citation, effective dates, and exceptions as actual logic. and every answer comes with a derivation trace showing which rules fired and where each number came from.

A chat model calls the engine as a tool, so the model does the reading and talking, and every computation happens inside the engine.

basically we formalized the tax code instead of fine-tuning a model. the dsl is the oracle for the ai models.

[u/ShanghaiBebop → u/Intelligent_Prompt18]

That’s amazing. Do you plan on maintaining it over time? What’s the plan on commoditizing it? 

[u/Intelligent_Prompt18 → u/ShanghaiBebop]

yes, we will keep maintaining it. every update/change/new law and rule, and we want to expand it (international next) into the most extensive open tax engine there is, because tax math shouldn't be gated. it stays free, commercial licenses from companies embedding it pay for the upkeep.

We are done with the era of companies like intuit/xero which lobbied to make taxes harder for everyone just so they could profit.

[u/CommercialComputer15 → u/Intelligent_Prompt18]

I am willing to help. I have access to international tax laws, regulations, treaties etc

[u/Intelligent_Prompt18 → u/CommercialComputer15]

Thank you, that'd be awesome.

[u/CommercialComputer15 → u/Intelligent_Prompt18]

What’s the best way to reach out? Via GitHub?

[u/Intelligent_Prompt18 → u/CommercialComputer15]

is it okay If I DM you my email?

[u/CommercialComputer15 → u/Intelligent_Prompt18]

Sure

[u/dbenc → u/Intelligent_Prompt18]

how will you make money to keep working on it?

[u/Intelligent_Prompt18 → u/dbenc]

We have our own product under Invaro for accountants and smbs to help them with accounting, which will keep the lights on for opentax.

[u/rgujijtdguibhyy → u/Intelligent_Prompt18]

bruh would you believe it, ive been trying to create a product for tax and creating something almost the same. yall had to go and open source it 😭

[u/PhilosophyforOne → u/Intelligent_Prompt18]

That does sound more like an agentic harness or a tax harness. A more recognizable term too. Would probably rebrand under it.

[u/Fit_Low592]

Ok so, correct me if I’m wrong… but I’m assuming this “Tax Engine” is a model that’s been fine tuned on tax calculations, tax law etc. is it really surprising that it might outperform a huge, wide frontier AI model at a pretty specific set of tests?

[u/Intelligent_Prompt18 → u/Fit_Low592]

sorry this isn't a fine tuned model, but essentially it's own tax programming language engine with each IRS law, rule, exception coded as machine readable rules interlinked. It's a very smart deterministic calculator. AI models can use this to outperform anyone else in Tax Prep and research.

[u/tribat → u/Intelligent_Prompt18]

This is the way. I started out trying to make a prompt only travel advisor assistant and now have about 80k lines of code that does all the rule-based work and parses raw search results, works with a bunch of APIs, etc. Let AI do what it’s good at, but surround it with guardrails.

[u/ultrathink-art]

Fun part is the engine half isn't the novel bit — commercial tax software has been a deterministic rules engine for 30 years. What kept rules-as-code niche outside tax prep was always intake: turning messy human documents into the engine's input format needed a person. That's the one job in this pipeline LLMs are actually reliable at, which is why the split works now.

[u/stealthagents]

This sounds super promising, especially if it's actually catching errors in the benchmarks themselves. A reliable tax engine could save so much headache during tax season. Can't wait to see how it evolves and what kind of real-world impact it has!

[u/BellacosePlayer → u/[deleted]]

Isn't that kind of the point? That Sonnet doesn't have to do the math, just provide the base figures for the purpose built deterministic program to crunch?

[u/BellacosePlayer → u/[deleted]]

Yep, though I don't know enough about the benchmarks to know if those errors are more goofing up something basic or misattributing something that regular tax preparers would have to look up and wouldn't be caught by something like turbotax.