About Sysadmin Toolbox

Why this site exists

Sysadmin Toolbox started from a familiar annoyance: needing a quick subnet calculation, a JWT decoded, or a cron expression explained, and having to pick through a page of ads, a login wall, or a "paste your data here" form on a site with no clear privacy policy. Most of what a sysadmin reaches for during a normal day — converting a timestamp, checking a DNS record, formatting some JSON, generating a password — doesn't need a server at all. It's arithmetic and string manipulation that a browser can do in milliseconds. This site is an attempt to put a wide set of those tools in one place, built so that using them doesn't require trusting a third party with whatever you happen to be working on.

What "runs in your browser" actually means

For the great majority of tools here, the JavaScript that does the work — parsing, hashing, encoding, calculating — runs locally on your machine, inside the tab you have open. Nothing you type into the subnet calculator, the JWT parser, the regex tester, or the password generator is sent to this site's server or anywhere else; there's no network request to intercept because none is made. A smaller set of tools, grouped under "Network Diagnostics" and parts of "Email Tools," genuinely can't work that way — resolving DNS, opening a TCP connection, or querying a WHOIS registry are operations a browser sandbox won't allow a page to perform directly. Those tools use this site's own backend to make the request on your behalf, and each one says so on its own page before you use it. The full breakdown is in the privacy policy.

How the tools get built

Every tool that implements a real algorithm or format — bcrypt, DNSSEC validation, ASN.1 parsing for certificate decoding, the NTP client, YAML/TOML/HCL parsing — is written and tested standalone against known-good reference data or an established library before it's wired into the site. That's a deliberate choice: a tool that silently produces a wrong subnet mask or a wrong hash is worse than not having the tool at all, so correctness is checked before anything ships, not after a bug report comes in.

How the site is run

Sysadmin Toolbox is a one-person project, run and maintained outside of normal working hours. It's free to use, with no account, no paywall, and no tool locked behind a tier. The site is supported by a small amount of advertising and by voluntary support through the Ko-fi link in the sidebar — neither is required to use anything here, and neither changes what data the tools do or don't collect (see the privacy policy for that). There's no roadmap promised and no SLA; tools get added and fixed as time allows, generally in batches, driven by what would actually be useful to reach for during real sysadmin work.

Feedback and requests

If a tool has a bug, produces a wrong result, or you'd like to see something added, there's a feedback form for exactly that — it goes straight to me, not a support queue.

This page describes how the site is built and run; it isn't a policy document — see the Privacy Policy for that.