About Us

Zellio.io is a collection of 77 small, single-purpose tools for the kind of technical chores that interrupt a working day — formatting a stubborn JSON payload, stripping metadata from a photo before sending it, working out what a cron expression actually does, converting a timestamp someone pasted into a ticket. Alongside them sit 281 reference entries across 10 collections and 12 longer guides.

All of it is free, none of it requires an account, and every tool runs entirely inside your browser.

The one rule

Your data never leaves your device. That is not a privacy policy flourish — it is an architectural constraint that decides what can and cannot be built here. There is no upload endpoint, no processing server, and no account system, because none of those exist in the design. When you compress an image, the compression happens in your browser using the same rendering engine that draws the page. When you hash a string, it is your browser's own cryptography doing it.

The practical consequence is that we cannot see your files or your text, even if we wanted to, and even if you asked us to for support. It also means several obvious tools do not exist here and never will: anything requiring storage, sharing by link, or a login is a different kind of product.

How the content is checked

Reference material about regular expressions, cron schedules and shell commands is unusually easy to get wrong and unusually easy to publish anyway, because a plausible pattern looks exactly like a correct one. So the published examples are executed rather than proofread.

Every regular expression in the Library is run against its own listed matches and non-matches before each release; if a pattern no longer accepts what the page claims it accepts, or accepts something the page says it rejects, the release is blocked. Cron expressions are parsed with the same engine that powers the on-site cron tool. Fill-in-the-blank templates are checked so that every placeholder has a field and every field is used. Published JavaScript must parse. Links to our own tools must resolve to pages that exist.

This has caught real errors — a pattern whose documented edge case did not behave as written, a command whose flag combination would have killed more processes than intended, a spreadsheet formula described with the wrong argument order. Those corrections are recorded in the changelog. If you find something still wrong, please tell us — factual corrections are made promptly and are not quietly overwritten.

How the site is paid for

Zellio.io is funded by advertising. There is no paid tier, no usage cap held back for subscribers, and no feature withheld to sell later — every visitor gets the same tools.

Advertising has one honest consequence worth stating plainly: ad and analytics scripts are third-party code, and they are the only part of the page that talks to anyone other than your own browser. What they collect, and how to refuse it, is set out in the privacy policy. Visitors in the EEA, the UK and Switzerland are asked for consent before any of it loads. The tools themselves are unaffected either way; they do not report what you do with them.

What we get wrong

Browser-based processing has real limits, and pretending otherwise would be the easiest way to waste your time. Very large files are bounded by your device's memory rather than by a server's. Some tools are slower than a desktop equivalent because they are doing the work locally. Optical character recognition and background removal are approximate by nature. Where a tool has a known limitation, the tool's own page says so rather than leaving you to discover it.

Get in touch

Bug reports, tool requests, corrections and security findings all go to hello@zellio.io. The contact page explains what to include to make each kind of message actionable, and the security page covers scope and disclosure. Every message is read.