Support this course

The sixteen lessons are free and will stay free. There is no account, no trial and no lesson that ends halfway with a price. This page says how the site is paid for, what money can and cannot buy here, and what a sponsor is and is not allowed to do.

Everything commercial on this site is switched on by its owner one piece at a time, and whatever is for sale shows up on this page with its price. If you see no price and no payment link below, nothing is being sold or asked for today, and you can close this tab and go back to the lessons.

What is free, and stays free

All sixteen lessons, with every question, prediction and reveal.
Every lab, its hidden tests, its hints and its reference solution.
The four checkpoints, both side quests and the glossary.
The capstone, both stages, and its download bundle: harness.py, adapter.py, lab.py, the tests, run_local.py and real_tools.py. Taking your harness out of the browser is the point of the course, so it is not the part with a price on it.

This is a promise, and it is also a fact about how the site works. The site is a folder of static files. Your browser has to download a reference solution before it can show it to you, so every solution is public by construction, and so is every test. Charging for something that is already one request away would be dishonest. Nothing that ships on this site is ever described as paid.

What money can buy, when something is for sale

The rule: a paid product here is packaging and depth on top of the free course, never a missing piece of it. Paid files are delivered by the checkout provider and are never hosted on this site, so there is nothing locked here to unlock. These are the kinds of thing the owner may put on sale. None of them is a piece of the sixteen lessons.

A one-time pack. The finished harness as a git repository with one commit per lesson, with its tests and a pytest entry point; the course as a single document for reading offline; and a copy of the whole site that runs from a folder on your machine. Every file in that repository can be rebuilt from the free course. You would be paying for the packaging, not for access.
Advanced modules, delivered with the pack as they are written. They are numbered A1, A2 and so on, never 17 and up: the course is sixteen lessons and is complete without them. A module that does not exist yet is not sold.
A team licence. The same pack for several people, with an invoice a company can file and permission to use the material in internal training.
A tip. A way to say thanks, once or monthly as the tipping service allows, with nothing delivered in return.

One-time means one-time. There is no subscription to the lessons and there will not be one: a finished course is a bad thing to rent, and a static site has no login to check. There are no countdowns, no discounts that expire tonight and no "most popular" ribbon.

Sponsor and ads policy

The sixteen lessons are free and carry no advertising inside them. A page may show one clearly labelled sponsor message, below the lesson navigation, after you have finished. It is a static link: no tracking, no animation, no pop-ups, ever. Sponsors have no say in what the lessons teach. If you have supported the course you can switch sponsor messages off on this page; it is an honour system. The site works fully with an ad blocker on.

In detail. The first two rules are checked by the program that builds the site, and a page that breaks one fails the build. The last two are promises from the owner:

At most one sponsor message on a page: below the navigation at the end of a lesson or side quest, at the foot of the syllabus and the glossary, and nowhere else. Nothing commercial sits between a lesson's first word and its last, so nothing interrupts a question, a prediction, a lab or a figure.
Lessons 1 and 2 and the capstone never carry a sponsor message. First impressions belong to the course, and the capstone's adapter is written against one provider's wire format, which is the wrong place for anybody's logo.
The message is always labelled sponsor, and a direct sponsor's link is marked rel="sponsored". The build writes both, so neither can be left off.
A sponsor is never named inside a lesson and has no say in what a lesson teaches or which tools it mentions.
A sponsor message is not an endorsement in either direction. The line in the footer stays true: this site is not affiliated with or endorsed by any model provider.

The supporter checkbox

When sponsor messages or support prompts are switched on, this page shows a checkbox: "I have supported the course". Ticking it hides sponsor messages and "support the course" prompts in this browser. That is all it does.

It is an honour system. Nobody checks a receipt, and the site has no way to. Anyone can tick it. A visitor who ticks it without paying would have blocked the message anyway.
It unlocks nothing, because nothing on this site is locked.
It is one value in this browser's storage, hfp:supporter. It is not sent anywhere. It travels in your progress export, so it survives a move to another browser, and unticking the box removes it.
It needs JavaScript. Without JavaScript the checkbox is not shown, and a sponsor message that is plain HTML cannot be hidden.

Questions

Will a lesson ever move behind a paywall?

No. Each lesson page is what people find, link to and teach from, and the course's promise is that you build the whole thing. Charging for lesson 12 would break that promise at the moment you are most invested. The technical reason is above: a static site cannot hide a file.

Is there a certificate?

No. Your progress lives in your own browser's storage, where you can edit it, so the site cannot know who did the work. A certificate issued on that basis would be a picture. The syllabus page shows what you have built, for your own use.

Who is the seller, and what about refunds?

When something is for sale, the payment happens on the checkout provider's own pages. The provider takes the payment and sends you the receipt and the files. This site never sees your card and learns nothing about the purchase. The owner sees what a checkout provider shows any seller, typically your name, your email address and what you bought. Refund terms, when the owner has published them, are at the bottom of this page; the provider's own terms apply either way.

What does this site know about me?

Very little, and nothing you type. Your answers, code and progress stay in your browser. The privacy page lists every request your browser makes and to whom.

Does any of the money go to Tau?

No. Tau is an independent open-source project under the MIT licence, and the lessons quote it as the reference implementation. This site is not part of Tau and is not endorsed by its authors, and nothing paid here reaches them. If Tau is useful to you, support it where it lives. Licences and attribution has the details.

Can I use what I build here at work?

Yes. The Python you write and the reference solutions are yours to use anywhere. The terms for the course text and figures are on the licences page.