0s and 1s CIS calculators MCP Server

Install 0s and 1s CIS calculators MCP server

claude mcp add --transport http cis https://0sand1s.co.uk/mcp

{
  "mcpServers": {
    "cis": {
      "url": "https://0sand1s.co.uk/mcp"
    }
  }
}

{
  "mcpServers": {
    "cis": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://0sand1s.co.uk/mcp"
      ]
    }
  }
}

{
  "servers": {
    "cis": {
      "type": "http",
      "url": "https://0sand1s.co.uk/mcp"
    }
  }
}

{
  "mcpServers": {
    "cis": {
      "serverUrl": "https://0sand1s.co.uk/mcp"
    }
  }
}

Context tax

Connecting this server adds ~2,252 tokens of tool definitions to every model turn (moderate, 7 tools). Measured 2026-10-19 via its hosted endpoint; o200k tokenizer, worst case for clients that load all tools up front. How we measure

Input prices as of 2026-10-06. Excludes your own prompt and output.

Tools (7)

• cis_late_penalties400 tok

  Works out the late filing penalties on one monthly CIS return under Finance Act 2009 Schedule 55: £100 the day after the 19th, £200 at 2 months, then the greater of £300 and 5% of the deductions at 6 and at 12 months (5% alone for a first return). Takes the tax year and month, the filing date or none, today's date, the deductions and whether a return had been filed before. Returns each penalty with its date and whether it is charged, avoided or still to come. Does not cover deliberate withholding, interest on late payment, or appeals.

• cis_nil_return_check384 tok

  Says whether a contractor must file a CIS nil return for a tax month (SI 2005/2045 reg 4(9A) and (9B), inserted by SI 2026/289 from 6 April 2026): due when a mainstream contractor that has paid subcontractors before pays none that month, unless it told HMRC no later than 14 days before the month started. Takes the tax year and month and yes or no answers. Returns whether a nil return is due, why, and the date it is due. Does not file anything.

• cis_gross_payment_turnover_test348 tok

  Checks the turnover test for CIS gross payment status (Finance Act 2004 Schedule 11, SI 2005/2045 reg 28): £30,000 net construction turnover for a sole trader; for a partnership or company, the lower of £30,000 for each partner or relevant person and £100,000. In a close company, shareholders count as well as directors. Returns the figure needed by each route, which one applies, and how far short. Covers the turnover test only, not the business test or the compliance test.

• cis_deduction343 tok

  Works out the CIS deduction on a payment to a subcontractor, from the gross bill to the net payment. Takes the gross including VAT, the VAT, the subcontractor's materials and the rate (0, 20 or 30). VAT is never taxed under CIS and materials come off before the rate applies; the deduction is rounded down to the penny. Returns each step of the working, money in pence and pounds. Does not cover retentions, or decide which rate applies (verify the subcontractor with HMRC for that).

• cis_gross_up271 tok

  Finds the gross amount (excluding VAT) that leaves a given net payment after the CIS deduction, for a subcontractor quoted a take-home figure. Takes the net, the subcontractor's materials and the rate (0, 20 or 30). Where rounding lets two grosses give the same net, the larger is returned so CIS is never under-deducted. Returns the forward working on that gross, money in pence and pounds. VAT is not included; add it on top if the subcontractor charges it.

• cis_needs_verification250 tok

  Says whether a contractor must verify a subcontractor with HMRC before paying them (SI 2005/2045 reg 6): not needed if the subcontractor was on one of this contractor's CIS returns, or was verified by this contractor, in the tax year of the payment or the two before. Takes the payment date, the tax years the subcontractor was on a return and the last verification date, all supplied by the caller. Does not contact HMRC or verify anyone, and does not cover group companies or business transfers.

• cis_tax_month162 tok

  For a date, gives the CIS tax month it falls in (the 6th to the 5th), the tax year, the date the monthly return (CIS300) is due (the 19th, also the date for paying HMRC by any means other than electronically), and the date for paying HMRC electronically (the 22nd, moved back to the banking day before when the 22nd is a weekend or an England and Wales bank holiday). Bank holidays are known to bank_holidays_known_until; after that only weekends move the date.

Security signals

97/100 — no known issues found as of 2026-10-19, from the checks below. This is not a guarantee of safety; review what a server can do before connecting it.

Scan it yourself before installing with vectra-guard, the open-source agent security CLI. Scoring rules

Freshness

Active — last maintenance signal today. The newest of the signals below sets the band.

1. Last commit (default branch)

   2026-10-18 · today · GitHub

2. Latest release

   no data · GitHub

3. Package published

   no data · npm/PyPI

4. Registry entry updated

   2026-10-18 · today · official registry · v1.0.1