Sheet & Flow Landlord Math

Sheet & Flow Landlord Math (MCP server)

Landlord and rental-property calculators as Model Context Protocol tools, so Claude, Cursor, VS Code or any MCP client does the math the same way every time instead of estimating it.

• Offline and deterministic. No network calls, no API keys, no data leaves your computer.
• No dependencies. Plain Node.js (18+), about 380 lines you can read.
• Tested. 552 randomized cases against an independent Python model, and the worked examples from the Sheet & Flow tutorials, on Node 18, 20 and 22 in CI. The rental math was also cross-checked against spreadsheet-recalculated (LibreOffice) deals before release.

Tools

Tool	What it answers
rental_property_analysis	Year-one NOI, monthly and annual cash flow, cap rate, cash-on-cash, DSCR, gross rent multiplier, break-even occupancy, expense ratio
mortgage_payment	Monthly principal and interest, total interest
short_term_rental_analysis	Airbnb/VRBO booked nights, stays, gross revenue, cash flow, RevPAR, what each booked night is worth, break-even occupancy and break-even nightly rate
rent_late_fee	Days late and the late fee: grace period, flat + percent + daily fees, a cap; optional Colorado / New York / Texas examples
lease_renewal_notice	Date the renewal or rent-increase notice must go out, 0-30/31-60/61-90 day window, status, next lease end
irs_mileage_deduction_2026	2026 IRS standard mileage deduction (business 72.5¢ Jan–Jun, 76¢ Jul–Dec)

Percentages are fractions (0.25 = 25%). Dates are YYYY-MM-DD. A percentage passed as 7 instead of 0.07 is rejected with a clear message rather than silently computed.

Install

Claude Desktop (one click): download sheet-and-flow-mcp-<version>.mcpb from the latest release and open it.

Any MCP client (stdio): clone the repo and point your client at server/index.js:

{
  "mcpServers": {
    "sheet-and-flow": { "command": "node", "args": ["/path/to/sheet-and-flow-mcp/server/index.js"] }
  }
}

Docker: docker build -t sheet-and-flow-mcp . then use {"command": "docker", "args": ["run", "-i", "--rm", "sheet-and-flow-mcp"]} in your client config.

It is also listed in the official MCP Registry as io.github.onyxaholguin-cyber/sheet-and-flow-mcp.

Install as an agent plugin (Grok Build, Cursor, Claude Code)

This repo is also a plugin: the MCP server plus three skills that tell the agent when and how to use it.

Skill	Use it for
landlord-deal-analysis	"Does this duplex / Airbnb cash flow?", cap rate, cash-on-cash, DSCR, break-even occupancy
rent-late-fee	Days late and the late fee, with optional Colorado, New York and Texas limits
lease-renewal-notice	When the renewal or rent-increase notice must go out, for one lease or a list

Manifests: .grok-plugin/plugin.json, .cursor-plugin/plugin.json, .claude-plugin/plugin.json; MCP config: .mcp.json.

Privacy and terms: PRIVACY.md (no data collected).

Network and credentials (declared for reviewers): none at run time. The server makes no network calls, reads no files and needs no API key or account. At install time, .mcp.json runs npx -y github:onyxaholguin-cyber/sheet-and-flow-mcp#<full commit sha>, which downloads this repo at that exact pinned commit from GitHub (the package has zero dependencies). test/plugin_check.py fails CI if the pinned commit's server/ differs from the tested code.

Example

Ask: "Airbnb deal: $350,000, 25% down at 7%, $185 a night, 62% occupancy, 14 blocked nights, 3.2-night stays, $95 cleaning fee, $85 cleaning cost, 15.5% host fee, 9% maintenance, $920/month fixed costs, $10,500 closing, $25,000 furnishing. Does it cash flow?"

short_term_rental_analysis returns, among other fields:

{ "monthlyCashFlow": -208.64, "keptPerBookedNight": 135.53, "breakEvenOccupancy": 0.6726, "breakEvenNightlyRate": 200.24 }

So the deal loses about $209 a month as quoted; it needs 67.3% occupancy at $185, or $200.24 a night at 62%. The same example is worked step by step in the short-term rental calculator tutorial.

How the math works

Every formula is explained in a free tutorial:

• Cap rate, cash-on-cash and DSCR and the free rental deal calculator
• Short-term rental break-even occupancy and nightly rate
• Rent late fee calculator (grace period, cap, state examples)
• Lease renewal tracker and notice dates
• IRS 2026 mileage log and the mileage deduction calculator

Prefer a spreadsheet?

The same math comes as finished Excel / Google Sheets workbooks from Sheet & Flow (paid; this server is free and MIT-licensed and doesn't need them): Short-Term Rental Deal Analyzer · Rental Property Deal Analyzer · Landlord Tenant Toolkit · Lease Renewal Tracker · Freelancer Mileage Log · Free Rental Cash Flow Calculator

Development

npm test                       # node --test, no install step
python3 test/model.py          # regenerate fixtures from the independent Python model
python3 scripts/build_mcpb.py  # build dist/*.mcpb and dist/server.json

Releases: pushing a v* tag runs the tests, builds the .mcpb, attaches it to a GitHub release and publishes server.json to the MCP Registry with GitHub OIDC (no stored tokens).

Disclaimer

Estimates for planning only. Not legal, tax or investment advice. The late-fee state examples are a summary of statute text as of October 2026; check current law, city rules and your lease before charging a fee.

MIT License © Sheet & Flow