Open source

Every tool here is arithmetic plus a form. The arithmetic is the part worth getting right, and the part worth checking — so it is published on its own, tested on its own, and licensed so anyone can use it for anything.

That is not generosity. A formula that only exists inside a web page cannot be reviewed, cannot be reused and cannot be corrected by someone who knows better. As a library it can be all three, and the tools on this site are better for it.

Everything you can work out about an image without decoding it: dimensions, format, resolution and EXIF orientation read straight from the bytes, resize and crop geometry, srcset generation, and print and screen sizing.

The awkward cases are the reason it exists. A phone stores a portrait photo as a landscape frame with a flag saying which way up it goes, so a program that reads the header naively puts every thumbnail on its side. Apple pads odd dimensions up to an even frame and carries a crop that takes them back, so a 37 by 23 pixel photo is stored as 38 by 24 — and is reported wrongly by most code that looks. Both are handled.

npm install tooltiki-image-tools

It is the same arithmetic as the image resizer, the format converters and the DPI calculator on this site, extracted and tested on its own.

Source on GitHub · Package on npm

Financial maths that shows its working: amortisation schedules row by row, APR with the fees actually counted, IRR and XIRR, compound growth, progressive tax with the per-band breakdown, and money that splits three ways without losing a cent.

It also models linear repayment — a Dutch lineaire hypotheek, a German Tilgungsdarlehen — where the same slice of principal is repaid every month and the instalment falls as the balance does. That is how a large part of Europe borrows, and nothing else on npm will draw it for you.

No tax rates are bundled with it. Bands move every January, and a library that ships them is wrong the following year and quietly wrong for anyone who did not upgrade, so they go in as data instead.

npm install tooltiki-financial

It is the same arithmetic as the mortgage calculator, the compound interest calculator and the inflation calculator.

Source on GitHub · Package on npm

Neither does the heavy lifting. The image library never decodes, encodes or resizes a single pixel — it computes the numbers you hand to something that does. The financial one has no ledger, no exchange rates and no notion of a transaction.

That boundary is the point. It is why both have no dependencies at all, why they run unchanged in a browser, a worker or on a server, and why each is small enough to read through in an afternoon and decide for yourself whether it is right.

MIT, both of them. Use them commercially, fork them, ship them inside something closed. There is nothing to ask and nothing to attribute.

If you find a wrong number, that is the report worth sending. For the financial library, include the source that settles what the right answer should be; for the image library, the file that reads back wrong. Both repositories take issues and pull requests.

More will follow as the categories with enough substance to stand alone get there. One repository per category regardless of whether the category has anything in it would be padding, not open source.