Tax Numbers in Claude

Questions it answers

Get the US federal tax numbers right, with the IRS document each one comes from.

Ask "what are the 2026 tax brackets for a married couple?", "what is the standard deduction for head of household?", "what was the IRS mileage rate on 15 March?", "when is the next estimated tax payment due?" or "roughly how much federal tax on 90,000 dollars of wages and 30,000 dollars of freelance income?".

Tax Numbers holds the federal tax figures for tax years 2025 and 2026: brackets, standard deduction, long-term capital gains thresholds, the Social Security wage base and self-employment tax, 401(k) and IRA limits, the estate and gift tax basic exclusion amount, the standard mileage rates, and the filing and estimated-payment deadlines. Every figure comes with the Revenue Procedure, notice or IRS page it was read from, and every answer says when the table was last verified. A year is added only after all of its figures have been checked.

It can also work out a simple federal estimate: standard deduction only, with self-employment tax, long-term capital gains and the Additional Medicare Tax. Every estimate lists its assumptions and what it leaves out (credits, state tax, alternative minimum tax, itemized deductions and more), and says it is an estimate and not tax advice.

It also answers a seller's question about registration: tax_duty takes where you sell from, where your buyers are (an EU country, the United Kingdom or a US state), what you sell and your yearly sales, and says whether you must register, the limit, the standard rate and how often you file. Every answer links the official tax authority page it comes from, shows the day that page was read and ends with a note to check with an accountant. It covers the 27 EU member states with the One Stop Shop limit of 10,000 euros, the United Kingdom and 14 US states. A place that is not in the table gets an explicit not covered answer with the list of places that are, never a guess. Reduced rates, local taxes, sales to businesses and domestic limits inside an EU country are not included.

It does not fill in or file returns, give advice on what to do, or cover US state income tax. Your figures are used for the one calculation and are not stored; the only lasting record is a daily count of calls per tool.

Short questions this server answers, each with a direct answer: 2026 Standard Deduction, Tax Brackets and Mileage Rate Lookup.

What it can do

• Looks up federal tax brackets, standard deduction and capital gains thresholds with IRS citations
• Gives the Social Security wage base and self-employment tax rules
• Gives 401(k) and IRA contribution limits
• Finds the IRS standard mileage rate for any date
• Lists filing and estimated-payment deadlines for a tax year
• Estimates federal tax with stated assumptions and exclusions
• Says if a seller must register for VAT or sales tax in the EU, UK or a US state, with limit, rate and filing
• Adds an official source link, the check date and an accountant note to every duty answer

Tools

• get_tax_parameters, Look up US federal tax figures. Use this when the user asks for a published US federal tax figure, for example "what are the 2026 tax brackets for married filing jointly", "standard deduction for head of household in 2025", "long-term capital gains thresholds", "Social Security wage base", "401(k) contribution limit". Pass the tax year (2025 and 2026), the topic (brackets, standard_deduction, mileage, retirement_limits, capital_gains, self_employment, estate_and_gift or all) and optionally the filing status (single, mfj, mfs, hoh). Returns rows with the figure and the IRS document and section it was read from, the year's status (current, or amended when a later law or notice changed a figure, with amended_by), and when the table was last verified. It does not give advice and does not cover state taxes.
• get_mileage_rate, Look up the IRS mileage rate. Use this when the user asks for the IRS standard mileage rate on a day, for example "what was the business mileage rate on 15 March 2026", "how much per mile can I deduct for charity driving", "medical mileage rate in 2025". Pass the date (YYYY-MM-DD); the rate in force that day is returned in cents per mile for business, medical and charity use, with the period it covers, the IRS notice that announced it and when it was last verified. Rates are available from 1 January 2022. It does not add up trips or compute a deduction.
• tax_deadlines, List US federal tax deadlines. Use this when the user asks when a US federal individual tax date falls, for example "when is the 2025 return due", "when is the extension deadline", "when is the next estimated tax payment due". Pass the tax year (the year the income was earned) and optionally as_of (today, YYYY-MM-DD) to get the next deadline. Returns the four estimated payment dates, the filing date and the extended filing date, each with whether the IRS publishes it or it follows the standing rule, and its source. Weekend and holiday moves are already applied. It does not cover state deadlines or disaster-relief postponements.
• estimate_federal_tax, Estimate US federal income tax. Use this when the user wants a rough US federal income tax figure, for example "how much federal tax on 90,000 dollars of wages", "estimate my tax with 40,000 dollars of freelance income", "what is my marginal rate". Pass the tax year, filing_status (single, mfj, mfs, hoh) and wages in dollars, and optionally self_employment_income, other_ordinary_income, long_term_capital_gains and adjustments. It uses the standard deduction and adds self-employment tax (with the Social Security wage base and the half-deduction), the Additional Medicare Tax and long-term capital gains rates. Returns taxable income, ordinary tax, capital gains tax, self-employment tax, total, marginal and effective rate, the assumptions made and a not_included list (credits, state tax, alternative minimum tax, itemized deductions and more). It is an estimate, not tax advice, and it is not a return.
• tax_duty, Check VAT or sales tax registration duty. Use this when a seller asks whether they must register for VAT or sales tax in a place, for example "I sell e-books from Germany and made 14,000 euros to buyers in France, do I need to register?" or "my US company sells SaaS with 150,000 US dollars of sales to Texas, do I owe sales tax?". Pass seller_country, buyer_place, product_kind and yearly_sales in the money of the buyer place (leave it out when unknown); add yearly_transactions for US states that also count sales. Returns must_register (yes, no or unclear), the limit, the standard rate, the filing rhythm, where to register, the reasons, official source links with the day each was checked, and a not-tax-advice note. Covers the 27 EU states (One Stop Shop limit of 10,000 euros), the United Kingdom and 14 US states; other places return not_covered with the covered list. It does not advise or cover sales to businesses, reduced rates, local taxes or a seller's own-country limit inside the EU, and it does not file or register anything.

Add Tax Numbers in Claude

Claude connects to a remote MCP server as a custom connector. The connection is made from Anthropic's cloud, not from your laptop, so the server must be on the public internet. Tax Numbers is. These steps were checked against Claude's custom-connector article (updated 2026-08-11) and the Claude Code MCP docs on 2026-10-01.

On a Pro or Max plan:

1. Open Customize, then Connectors.
2. Select the plus button, then Add custom connector.
3. Paste this URL. Leave Advanced settings empty: this server does not need an OAuth client id or secret.

   https://tax.openkrill.app/mcp

4. Select Add. The connector is yours. Anthropic has not reviewed it, and it is not a Directory listing.
5. In a conversation, open the plus button, then Connectors, and enable Tax Numbers. Ask: What is the 2026 standard deduction for a single filer?

On Team and Enterprise, an Owner adds the connector first at Organization settings, then Connectors, then Add, then Custom, then Web, and pastes the same URL. Members then connect it from Customize. A Free plan can add one custom connector.

In Claude Code, add it from the project directory:

claude mcp add --transport http tax https://tax.openkrill.app/mcp

That writes a local or user config. A JSON entry needs "type": "http" (or streamable-http) plus the url. An entry with a url and no type is skipped. Confirm with claude mcp get tax. The tools you should see are get_tax_parameters, get_mileage_rate, tax_deadlines, estimate_federal_tax, tax_duty.

If Claude tries to fetch https://tax.openkrill.app/mcp from its code sandbox and reports HTTP 403, the block is Claude's sandbox network allowlist, not this server. The sandbox proxy answers 403 with x-deny-reason: host_not_allowed for every host outside the allowlist. Use the connector above instead: connector calls come from Anthropic's cloud and do not pass the sandbox proxy. To let the sandbox reach it as well, an Owner adds tax.openkrill.app under Settings, then Capabilities, then Additional allowed domains.

Enable the connector only in conversations that need it. Claude can call the tools while you work, including during research, so turn off any tool you do not want invoked. Tax Numbers does not write to your accounts. It still receives the arguments of each call. Read the privacy page before you paste anything that is not public.

If it does not work

A call checked on 2026-10-17

The 2026 single-filer standard deduction is a published IRS figure in the plugin's table. It is not tax advice. The request below was posted to https://tax.openkrill.app/mcp as tools/call. HTTP 200. Source: the Tax Numbers server, read 2026-10-17.

{
  "method": "tools/call",
  "params": {
    "name": "get_tax_parameters",
    "arguments": {
      "year": 2026,
      "topic": "standard_deduction",
      "filing_status": "single"
    }
  }
}

• status. current
• year. 2026
• rows. 2 returned
• source document. Rev. Proc. 2025-32 (2026 inflation adjustments)
• source date. 2025-10-09

Repeat the call yourself if you need a newer reading. Cached answers expire. A rate limit is not a result: wait and try again. Nothing in the call is a ranking, a filing, or advice.

Using it in production

Nothing to install and nothing to run: no package, no Python or Node.js version and no environment variable. Tax Numbers runs on our servers, and your client only needs the URL https://tax.openkrill.app/mcp.

Use it in other apps

• Tax Numbers in ChatGPT
• Tax Numbers in Cursor
• Tax Numbers in VS Code
• Tax Numbers in Pi

Roles that use Tax Numbers

• Compliance reader guide

Frequently asked questions

Words on this page

• MCP (Model Context Protocol) definition
• Streamable HTTP transport definition
• Tool primitive definition
• Rate limit policy definition

Source: plugin listing for tax in this repository, and a live tools/call on 2026-10-17. As of 2026-10-17.