McpStamp Per Diem

mcp-per-diem

Work out the daily travel allowance for a business trip on the rate tables the tax authorities actually publish, and keep the trips you priced. You give it where you went, when you left and when you got back, and which meals somebody else paid for; it gives you the amount per day and the total, in the scheme's own currency, with the partial-day rule and every meal deduction shown next to the number that produced it. Three schemes ship with it: the Polish delegation regulation (domestic and per country), the HMRC benchmark scale rates for travel inside the UK, and the US GSA CONUS standard M&IE and lodging. The tables are bundled files, not a live feed, so the same trip priced twice gives the same answer, and every rate carries the regulation, the source URL and the date it took effect. Nothing leaves your machine.

Built by theluckystrike.

In the official MCP Registry (io.github.theluckystrike/per-diem).

[per-diem demo]

Install

One-click (.mcpb): download per-diem.mcpb from the latest release and double-click it in Claude Desktop: https://github.com/theluckystrike/mcp-servers/releases/latest

Hosted, no install: point a URL-based client at https://mcp.zovo.one/mcp/per-diem. GET https://mcp.zovo.one/mcp/connect mints a token and prints a ready URL.

npm publish for @theluckystrike/mcp-per-diem is pending, so the npx line below returns 404 today.

Claude Desktop (~/Library/Application Support/Claude/claude_desktop_config.json):

{  "mcpServers": {    "per-diem": {      "command": "npx",      "args": ["-y", "@theluckystrike/mcp-per-diem"]    }  }}

Claude Code:

claude mcp add per-diem -- npx -y @theluckystrike/mcp-per-diem

Cursor (~/.cursor/mcp.json or .cursor/mcp.json): the same entry as Claude Desktop.

Tools

Free vs Pro

Get Pro: $19 one-time, or $39 for the bundle.

What is in the tables, and what is deliberately not

Every table under src/tables/ carries a header with the authority, the instrument, the source URL, the date the rates took effect and the date they were read. perdiem_rates returns that header with the rates, so the provenance travels with the number.

The rule for what is in them: a value that could not be stated with confidence from the public regulation text was left out, not guessed. A per diem figure ends up on a tax return. A wrong one that looks authoritative is worse than an absent one, because an absent one is refused by name and you go and look it up.

Rates change. Check the effective_date in any answer before you rely on it, and read the source_url if the trip is recent.

Rules the calculator applies

• Start and end are instants, not wall clocks. Pass ISO 8601 with an offset (2026-03-28T22:00:00+01:00) or a local datetime plus an IANA timezone. Elapsed hours are an epoch difference, so a trip across a clock change is 23 or 25 hours, not 24.
• Poland counts 24-hour periods from departure. Under 24 hours domestically: nothing under 8 hours, half the diet from 8 to 12, the whole diet above 12. Over 24 hours: a whole diet per period, then half for a remainder up to 8 hours and a whole one above. Abroad the ladder is a third up to 8 hours, half over 8 and up to 12, whole above. Free meals take 25/50/25 percent off a domestic day and 15/30/30 off a foreign one.
• The UK pays by band: 5.00 GBP from 5 hours away, 10.00 GBP from 10, 25.00 GBP from 15 when the journey is ongoing at 8pm, nothing under 5. A provided meal removes its share of the band, pro rata. HMRC states the principle ("the rate is not payable for a meal that was provided"); the pro-rata arithmetic is this server's reading of it, and it says so in the answer.
• The US counts calendar days in the destination zone, at 75 percent of M&IE on the first and last day. A provided meal is deducted at its own published amount, and the 5.00 USD of incidentals is never deducted. Lodging is a cap on receipted reimbursement, not an allowance that is paid out; the answer says so every time.
• Currencies are never added together. There is no exchange rate in this server, so a PLN diet and a EUR one stay two figures.

Exporting to the expense tracker

trip_export returns the exact expense_add arguments for the expense-tracker server, one payload per currency, and writes nothing itself. That is deliberate: expense-tracker publishes no library entry point, and its id counter, its category rules, its VAT split and its currency defaults all live inside its own expense_add handler under its own lock. Appending a row to its data.json directly would produce an expense with none of those applied: one that looks native and is not. Handing back the arguments is the same contract kanban uses for time-tracker's timer_start.

No vat_rate is set on the payload. A statutory per diem is an allowance, not a purchase, so there is no input VAT to reclaim on it.

A measured insight

Substring matching a country name is how a per diem gets quietly priced at another country's rate.

The first build resolved a destination by exact name, then ISO code, then country.includes(destination). A trip to Oman came back priced, in EUR, with no warning: "romania".includes("oman") is true, so it took Romania's 42.00 EUR diet. Oman is not one of the 34 countries this build bundles, so the correct answer was a refusal naming the gap. Instead the caller got a confident number, in the wrong currency, from a country 3,000 km away.

The fix is one line, the fallback is a prefix match of four characters or more, and it is asserted in test/adversarial.test.mjs. The general form is worth more than the fix: a fuzzy match is safe when a miss is cheap and expensive when a miss is silent. Here a miss produces a tax figure, so the fallback has to fail closed. The table being deliberately partial is exactly what makes the substring fallback dangerous: with a complete table the wrong row is a near miss, and with a partial one it is a row that should never have matched at all.

Privacy

Everything stays on your machine. Trips are JSON under ${XDG_DATA_HOME:-~/.local/share}/mcp-servers/per-diem/. The rate tables are files inside the package. There is no network call anywhere in this server, no account and no API key. License keys are verified offline.

License

MIT. Support: [email protected]

Use these docs as an MCP server

Any MCP client (Claude, Cursor, Windsurf, VS Code) can read this repository's documentation directly via GitMCP - no install:

• Docs MCP URL: https://gitmcp.io/theluckystrike/mcp-per-diem