About 0s and 1s CIS calculators
The 0s and 1s CIS MCP server offers free calculators for UK Construction Industry Scheme contractors and bookkeepers, through a remote MCP server and JSON API. Results cite the GOV.UK and legislation.gov.uk pages used; they are not tax advice.
Key features
- 01Calculate CIS deductions and net payments
- 02Gross up a target net payment
- 03Work out tax months and payment dates
- 04Estimate late return penalties
- 05Check gross payment status and verification
- 06Check nil return requirements
Use cases
- 01Calculate CIS deductions on subcontractor payments
- 02Schedule CIS returns and electronic payments
- 03Check late penalties or nil return obligations
MCP support
The remote MCP server exposes seven CIS calculation tools, covering deductions, tax dates, penalties, and eligibility checks. No key or account is required; a REST JSON API is also available.
Configuration
Remote servers need no local install. Pick your client, then copy the config or install in one click.
https://0sand1s.co.uk/mcpclaude mcp add --transport http uk-co-0sand1s-cis https://0sand1s.co.uk/mcp{"mcpServers":{"uk-co-0sand1s-cis":{"type":"http","url":"https://0sand1s.co.uk/mcp"}}}Open in Cursor{"servers":{"uk-co-0sand1s-cis":{"type":"http","url":"https://0sand1s.co.uk/mcp"}}}Open in VS Code{"mcpServers":{"uk-co-0sand1s-cis":{"type":"http","url":"https://0sand1s.co.uk/mcp"}}}{"mcpServers":{"uk-co-0sand1s-cis":{"serverUrl":"https://0sand1s.co.uk/mcp"}}}Run commands in a terminal; paste JSON into the client’s MCP config and restart. Servers that need sign-in will prompt on first connect.
Tools
Details
From the project README0s and 1s CIS MCP server
Free calculators for the UK Construction Industry Scheme (CIS), as a remote MCP server and a JSON API. For contractors who pay subcontractors, and the bookkeepers who do it for them.
- MCP server:
https://0sand1s.co.uk/mcp(Streamable HTTP, no sign-in) - REST API:
https://0sand1s.co.uk/api/v1(OpenAPI) - Docs: https://0sand1s.co.uk/developers
No key and no account. Nothing you send is stored. Up to 60 requests a minute from one address, the API and the MCP server together.
Tools
| Tool | What it works out |
|---|---|
cis_deduction | The CIS deduction on a payment: gross, VAT and materials in, deduction and net out, with the working |
cis_gross_up | The gross to pay so the subcontractor receives a given net |
cis_tax_month | The tax month a date falls in, the return due date (19th) and the electronic payment date (22nd, moved for weekends and bank holidays) |
cis_late_penalties | What a late CIS300 or nil return costs, stage by stage |
cis_gross_payment_turnover_test | Whether a business meets the turnover test for gross payment status |
cis_needs_verification | Whether a subcontractor must be verified with HMRC before a payment |
cis_nil_return_check | Whether a nil return is due for a tax month |
Money goes in as pounds ("1,200.00") and comes back as pence and pounds. Dates are YYYY-MM-DD. Every answer lists the GOV.UK and legislation.gov.uk pages it follows. Answers follow the published rules; they are not tax advice and do not come from HMRC.
Connect
Claude (claude.ai and the desktop app): Customize, Connectors, Add custom connector, then name it 0s and 1s with the URL https://0sand1s.co.uk/mcp.
Claude Code:
claude mcp add --transport http 0sand1s https://0sand1s.co.uk/mcp
Cursor (~/.cursor/mcp.json):
{ "mcpServers": { "0sand1s": { "url": "https://0sand1s.co.uk/mcp" } } }
VS Code (.vscode/mcp.json):
{ "servers": { "0sand1s": { "type": "http", "url": "https://0sand1s.co.uk/mcp" } } }
Try the API
curl "https://0sand1s.co.uk/api/v1/deduction?gross=1200&vat=200&materials=300&rate=20"
About this repository
This repository holds the listing for the official MCP registry (server.json, name uk.co.0sand1s/cis) and this README. The server is hosted by 0s and 1s, CIS filing software for contractors. Questions: [email protected].
Comments
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