About DevTools

What this site is for

Splitting a subnet, looking inside a JWT, checking when a certificate expires — these are chores that come up several times a day. Instead of writing a throwaway script each time or pasting values into a site you do not trust, DevTools puts the tools you need in one place.

There are 25 tools across five groups: IP/subnet, DNS/network, web/security, encoding/conversion, and reference. Every tool page carries an explanation of what it computes, how to use it step by step, and the pitfalls that tend to catch people out, along with an FAQ.

Computation stays in the browser where it can

Subnet math, base conversion, Base64 and URL encoding, JWT decoding, hashing, regex testing — all of it runs inside your browser. What you type never leaves the page. That matters when you are handling internal IP ranges or tokens that must not go anywhere.

DNS lookup, reverse DNS, HTTP header inspection, SSL certificate checks, and the my-IP tool have to query the outside world, so they go through a server. Those tools are marked with an API badge. What the server receives and what it keeps is spelled out in the privacy policy.

Where the reference data comes from

The port list and HTTP status codes are grounded in the IANA registries and the RFCs, but they are not wholesale copies. Entries are selected for what you actually run into in practice, and each one carries our own note on why it matters or where people commonly get it wrong. Links to the upstream registries appear on each page.

The standards are always the authoritative source. Where our notes and the original disagree, follow the original — and please tell us so we can fix it.

Operation

This is a personal site, built and run by one developer. Ads cover the running costs. The tools are free, with no signup and no login.