MonsiTools

MonsiTools is a calculator builder. You type a formula in plain words, for example "price - product cost - shipping", and each word becomes an input field. The answer updates as you type, and you can save the calculator and share the link.

What you can do with it

Build a calculator from a formula. Write the math the way you would say it. MonsiTools turns the words into labelled inputs and shows the result as you change them.

Use ready-made calculators. The library covers ecommerce fees and margins, VAT, break-even, SaaS metrics like MRR and runway, loans, payroll and take-home pay.

Chain calculators into workflows. The result of one step feeds the next. For example, monthly revenue flows into runway and then into a rough valuation, or landed cost flows into price and then into profit per order. Change the first number and every step after it updates.

Embed a calculator on your own site. Each calculator has a short embed snippet, and the frame resizes to fit your page.

Let an AI assistant run the math. A remote MCP server and a JSON API let tools like Claude, Cursor or your own code look up a calculator, read its formula and run it, so the assistant returns an exact number instead of doing arithmetic in its head.

Who it is for

Online sellers checking marketplace fees and margins, freelancers working out a day rate, SaaS founders tracking revenue and runway, finance students checking homework, and developers who want deterministic calculations inside an assistant or app.

Pricing

No account is needed to start, there are no ads, and the numbers you type stay in your browser. Every tool has a limited free allowance (15 calculations without an account, 25 a month signed in). A paid Premium plan removes the limit and unlocks calculation through the API and MCP server.