0s and 1s CIS calculators

Connect it to your AI

Claude Code

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

Claude, ChatGPT, Cursor and other apps

Add it as a custom connector with this URL (Streamable HTTP):

https://0sand1s.co.uk/mcp

Cursor, VS Code and other apps (mcp.json)

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

Tools it offers

7 tools, as the server itself reported during our check on Oct 31, 2026.

• cis_deductionWorks 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 un
• cis_gross_upFinds 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). Wher
• cis_tax_monthFor 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 da
• cis_late_penaltiesWorks 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%
• cis_gross_payment_turnover_testChecks 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
• cis_needs_verificationSays 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
• cis_nil_return_checkSays 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

Questions