Single Page Sandbox is a free collection of seven single-file browser tools. Each one is a single HTML file you download and run yourself — unlock a PDF, build a fillable form, generate a QR code, design a banner, make a math worksheet, or check writing for AI.
The tool people arrive looking for most often.
Utilities · Featured
Tired of typing the password every time you open a PDF? Strip it out for good — one file, or a whole folder in a single pass. It decrypts with the password you supply and re-saves without it, so the file and the password never leave your computer.
Every tool below opens in the browser. Each one also downloads as a single HTML file you can keep and run offline.
Education
Custom math worksheets with auto-graded answer keys and printable certificates.
Free
One free newsletter subscription unlocks the whole sandbox — and new tools land there first.
Each topic page carries the formula, a worked example, sample problems with answers, and a link straight into Formula Worksheet Maker.
Yes. Every Single Page Sandbox tool is completely free — no paywall, no premium tier, no in-app purchase. The download is gated only by a free Substack newsletter subscription.
No. None of the tools require an account, login, or sign-in to use. The Substack subscription is for the newsletter, not for the tools themselves — you can also click "Already a subscriber" and proceed.
No. Every tool processes your text, images, and CSV files entirely inside the browser. Nothing is uploaded to a server. The site uses analytics internally to improve the experience — no content of what you type or generate is ever transmitted.
Most tools are, unless indicated otherwise. Each tool is a single HTML file. After you download the zip, extract home.html and open it directly in your browser — works fully offline with no internet connection.
Because the browser is the most universal runtime there is. A single HTML file bundles presentation, interactivity, and logic into one document that runs on practically any device — Windows, Mac, Linux, phone or tablet — with nothing to install. And it's no toy format: serious products like Figma and Google Docs run entirely in the browser. Running a tool locally, as a file you own, means no vendor lock-in, no subscription, and no handing your data to someone else's server — your work stays on your machine.
Nirav Bhatt at Brain Bound Learning. New tools and how-they-work deep-dives are posted on the Substack publication.
We try our best to make them safe. But we don't control the state of the user's machine, so we don't bear any legal liability for running them locally. See our Terms.
Tipsnguts stores a little data in your browser: local storage for app state (subscribe status, terms acceptance), and a random per-tab visit ID in session storage so we can count visits without cookies - it is deleted when you close the tab. Analytics are cookieless and aggregate; we do not profile you or track you across sites, and we skip the visit ID if your browser sends Global Privacy Control or Do Not Track. Learn more.