What is stored and what is sent

Last updated 4 September 2026.

This is a study site for the American Computer Science League. There are no accounts, no sign in, and no advertising. Most of what it knows about you never leaves your own browser, but one part of it does, and this page says exactly which part.

Kept in your browser

The following is written to localStorage on the device you are using. It stays on that device, is not sent to us, and does not follow you to another browser or another computer.

• Which division you are studying for, Junior or Senior
• Your light or dark theme choice, and which programming language you last used
• Whether you answered each practice question correctly, which is what fills the missed questions list
• Whether you have solved a programming problem or viewed its solution
• The code you write for each problem in each language, and any custom test input
• A mock exam in progress, including its questions, your answers so far, and its deadline

The Clear my progress button in the footer deletes all of it. Clearing site data in your browser does the same thing. Neither is recoverable, because there is no copy anywhere else.

No cookies

The site sets no cookies and runs no analytics, tracking pixels, or third party scripts. Its content security policy blocks scripts from anywhere other than this site, which you can check in your browser's network tools.

Sent when you run code

Pressing Run, Submit, or Run with this input sends three things to our endpoint at /api/run: the language you chose, the full contents of the editor, and the test input for that run. That is the whole request body. The request also carries the ordinary HTTP metadata described in the next section, as every web request does. Browsing the guides, answering practice questions, and taking mock exams send nothing at all.

We cannot compile or run anything ourselves, so that request is forwarded to Wandbox, a free public compiler service operated by a third party. Your code is executed on their infrastructure, not ours, and their handling of it is governed by their terms rather than this page. Treat anything you paste into the editor as leaving your machine. Do not put personal information, passwords, or schoolwork you are not free to share into it.

Ordinary request information

The site is hosted on Vercel. Like any web host, Vercel receives the normal information that comes with an HTTP request, including your IP address, the address you asked for, your browser's user agent string, and the time. That happens for every page you load, not only when you run code. Vercel processes this as the site's hosting provider, chosen and configured by us, and controls its own infrastructure and retention. It describes its handling of this in its privacy notice.

Our code runner keeps a short lived count of requests per IP address, in memory only, so that one visitor cannot exhaust the service for everyone else. It is not written to disk and does not survive the process. We do not keep our own logs of submitted code or input.

Age

This site is built for high school students. It is not directed at children under 13 and asks for no personal information from anyone. If you are a parent, teacher, or administrator with a question about how it is used at your school, please get in touch before assigning it.

Your practice scores are not an assessment

The study content, the answer key, the hidden test cases, and the reference solutions are all downloaded to your browser, and anyone can read them. Running code is the one thing that still needs the site's own endpoint and Wandbox. Scores here are for your own practice and are not suitable for grading.

Not affiliated with ACSL

This is an independent study resource. It is not affiliated with, authorised by, or endorsed by the American Computer Science League. Contest rules and formats change between seasons, so check acsl.org for anything official.

Contact and changes

Questions, corrections, or a request to have something removed can go straight to contact@sfhsacsl.org. For anything security related, including a vulnerability in this site or its code runner, write to security@sfhsacsl.org. Both reach a person and need no account.

If you would rather report something in the open, or privately through GitHub, there is the issue tracker and the security advisory form, both of which need a GitHub account. If this page changes materially, the date at the top changes with it.