0s and 1s CIS calculators
Free UK CIS calculators: deductions, deadlines, late penalties, gross payment test, verification.
Install
Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).
claude mcp add --transport http 0s-and-1s-cis-calculators 'https://0sand1s.co.uk/mcp'{
"mcpServers": {
"0s-and-1s-cis-calculators": {
"type": "http",
"url": "https://0sand1s.co.uk/mcp"
}
}
}Documentation
From the project's README on GitHub, refreshed weekly. Links open on GitHub.
0s 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/mcpCursor (~/.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: support@0sand1s.co.uk.
Frequently asked questions
What is 0s and 1s CIS calculators?
Free UK CIS calculators: deductions, deadlines, late penalties, gross payment test, verification.
How do I install 0s and 1s CIS calculators?
It runs as a remote server. In Claude Code: claude mcp add --transport http 0s-and-1s-cis-calculators 'https://0sand1s.co.uk/mcp'. For other clients, paste the JSON configuration from this page into their MCP settings.
Does 0s and 1s CIS calculators need an API key?
Its registry entry lists no required key or secret. Some features may still need an account with the service it connects to.
Is 0s and 1s CIS calculators open source?
Yes. Its code is on GitHub under the MIT license.
Who maintains 0s and 1s CIS calculators?
It is published by 0sand1s-uk. AI.tn lists it but does not maintain or endorse it.
From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.