# Grounding an LLM in real tax data with a public MCP server

> Source: <https://dev.to/d_edu_eebba6de1155fe/grounding-an-llm-in-real-tax-data-with-a-public-mcp-server-5h58>
> Published: 2026-08-19 04:26:39+00:00

We all know the failure mode: ask an LLM for a tax rate and it'll hand you a confident number with zero provenance. Fine for a demo, useless for anything you'd ship. The interesting question is how you *ground* the model in a source of truth — and MCP has quietly made that a one-liner.

Quick recap for anyone who missed it: **Model Context Protocol** is an open standard (Anthropic, late 2024) for connecting an assistant to external tools and data. Client support is now broad — Claude Desktop, Claude Code, ChatGPT, Cursor, VS Code, Windsurf.

2Fin runs a free public MCP server for tax at `taxmcp.ai2fin.com`

. No key, no auth. Point any MCP client at it:

```
{
  "mcpServers": {
    "tax": { "url": "https://taxmcp.ai2fin.com" }
  }
}
```

You get eight tools: `tax_rate_lookup`

, `compute_gst_vat`

, `income_tax_estimate`

, `company_tax_estimate`

, `cgt_estimate`

, `superannuation_estimate`

, `student_loan_repayment`

, `compare_countries`

— across 88 countries.

**Every response includes its source authority and a dataVerifiedOn date.** That's the part most "AI + data" integrations skip, and it's exactly what makes the output auditable instead of vibes. A wrong or stale number is

```
> income_tax_estimate { country: "AU", income: 95000 }
< { incomeTax: ..., medicareLevy: ..., takeHome: ...,
    source: "ATO — ato.gov.au", dataVerifiedOn: "2026-06-01" }
```

The same engine backs their web calculators, so the MCP answers and the site can't drift apart — which, if you've ever maintained two copies of the same rate table, you'll appreciate.

Good worked example of the pattern: don't make the model *remember* facts, give it a tool that *fetches* them with a citation attached. The tax domain just makes the stakes obvious — but the same design applies to any data your assistant has no business memorising.

If you want to poke at it, it's free and needs no account: [taxmcp.ai2fin.com](https://taxmcp.ai2fin.com).