# OpenTax Muse connector

From musedirectory.ai, the independent directory of Meta Muse connectors. Not affiliated with Meta.

## OpenTax

Verifiable US tax computation backed by cited federal and state tax rules for individuals and businesses.

- Record: https://musedirectory.ai/connector/opentax
- Category: Finance & Bills
- Developer: Invaro
- Muse status: Extra setup. Not in Muse's Connectors list yet. Muse can still use it: its page gives you a request to paste into Muse.
- Health: Working, 2457ms, checked 2026-09-28T08:15:48Z
- Endpoint: https://opentax.invaro.ai/mcp
- Auth: No account needed; Pricing: unknown
- Screening: Screened, no issues found (2026-09-24T03:00:58Z)
- Source: Found in the official MCP Registry (io.github.Invaro/opentax) https://registry.modelcontextprotocol.io/v0/servers?search=io.github.Invaro%2Fopentax

Computes federal individual income tax, business entity tax, estate and trust tax, and state returns (15 states) from a machine-checkable corpus of tax rules. Returns tax amounts with full derivation proofs and citations so results can be verified offline.

Example request: "Calculate my 2025 federal income tax from my W-2 wages, investment income, and dependent children."

How to connect: Not in Muse's Connectors list yet, but Muse can still use it. Paste this into Muse: "Use OpenTax to help me. It is a free service with an MCP server at https://opentax.invaro.ai/mcp. It does not need an API key. Ask me before you share anything with it." Muse asks before it shares anything with the app's site. Meta does not review apps used this way, so only use ones you trust. We tested this in the Muse app on September 24, 2026: Muse used an app's link directly this way and returned a live answer.

Tools:
- calculate_tax: Compute US federal INDIVIDUAL income tax (or balance due if withholding is given) from a content-addressed corpus of cited rules. NEVER estimate tax yourself — call this, and report ONLY numbers returned by oracle calls made with the real facts (never hand-check or approximate a 
- calculate_business_tax: Compute US federal BUSINESS-ENTITY tax from the same cited corpus: check-the-box entity classification, Form 1120 corporate income tax (§ 179/168(k)/174A/163(j)/DRD/NOL, § 250, GBC/FTC/BEAT), S-corp entity taxes, corporate estimates, the § 4501 buyback excise, AET and PHC taxes. 
- calculate_fiduciary_tax: Compute US federal income tax for an ESTATE or TRUST (Form 1041): the § 1(e) compressed brackets and § 642(b) exemption. Input is taxable income before the exemption, after the §§ 651/661 distribution deduction. Retained capital gains refuse loudly (§ 1(h) trust breakpoints not m
- determine_dependent: Determine whether ONE candidate person is the taxpayer's § 152 dependent — qualifying child or qualifying relative, including multiple-support agreements and the divorced-parents release — as a proof-backed yes/no with citations. Feed the result into calculate_tax's credits group
- compute_state_return: Compose a STATE return's printed-form line set deterministically (2025 IL-1040 / VA 760 / CA 540 / NY IT-201 / PA-40 / NJ-1040 / OH IT 1040 / NC D-400 / GA 500 / MD 502 / MO-1040 / WI Form 1 / MN M1 / SC1040 / AL Form 40 / OR-40 / OK Form 511 / CT-1040 / KS K-40 / AR AR1000F / NM
- compute_return: Compute the COMPLETE Form 1040 bottom-line set in one call — the 17 lines that determine the return (1a, 9, 10, 11, 12e, 15, 16, 17 AMT, 19, 22, 23, 24, 25d, 27a, 28, 32, 33, 34/37), each whole-dollar rounded by the engine. Takes the SAME input as calculate_tax (prefer the docume
- verify_tax_claim: Verify a claimed tax amount (yours, a user's, or another tool's) against the law. Returns verdict 'verified' or 'refuted' with the correct value. Use this as a self-check before presenting any tax number. Put asOf (and target, if any) INSIDE the facts object — e.g. facts: {..., "
- list_input_facts: Discover every input the tax corpus understands: id, type, whether required, and its documented default. Call this if unsure what information to collect from the user.
- explain_rule: Get a tax rule's statutory citation, verbatim excerpt, validity window, parameters, and dependencies. Use to quote the actual law behind an answer.
- find_tax_cliffs: Find exact dollar amounts where one more cent of an input costs MORE than a cent of tax (marginal rate over 100%) — e.g. the EITC investment-income kill switch, CTC phase-out steps. Every probe is a real evaluation.
- compare_filing_statuses: Compute the answer under every filing status for the same facts — e.g. to answer 'should we file jointly or separately?'. Statuses that need more facts report their error instead of guessing.
- lookup_tax_parameter: Look up the current-law dollar amounts behind a question ('standard deduction', 'CTC phase-out threshold', 'tips deduction cap') with their statutory citations and validity windows. Use this to fact-check ANY tax number before stating it — your training data likely predates the O
- search_tax_rules: Full-text search over the encoded tax-law corpus ('kiddie tax', 'NIIT threshold', 'california renters credit'). Returns matching rules: id, title, statutory citation, effective window, and a verbatim excerpt of the law text. A hit means the engine computes this; zero hits means i
- verify_fact: Fact-check a claimed dollar amount about tax law ('the 2026 MFJ standard deduction is $32,200', 'CTC is $2,000 per child') against the corpus. Returns verified / refuted (with the correct value and citation) / unknown. Never states a verdict it cannot ground.
- is_tipped_occupation: Determine whether a job is on the Treasury Tipped Occupation list (Treas. Reg. § 1.224-1, final Apr 2026) for the § 224 'no tax on tips' deduction. Fuzzy-matches the job name; returns the official listing (name, TTC code, category) or a definitive 'not listed'.

Screening checks:
- MCP handshake: pass (Answered in 346ms)
- Domain against threat feeds (Cloudflare security DNS): pass (opentax.invaro.ai not flagged)
- Published packages against the OSV malicious-package database: pass (No malicious-package advisories)
- Hidden instructions or invisible characters in tool text: warn (compute_state_return: Unusually long tool description)
- Inputs asking for passwords, card numbers or seed phrases: pass (None found)
- Domain and redirects: pass (No redirects off the domain)
- AI review of purpose and tool behavior: pass (No concerns)