Developer cheat sheets
Five tools for things you look up again and again and never quite memorise. What is the difference between a 401 and a 403? When does 0 9 * * 1-5 run? Which versions does ^1.4.0 accept in package.json? Each one answers with your actual input instead of sending you off to read the whole spec.
The HTTP list covers every code from 100 to 511, with its RFC and when to use it. The cron explainer turns an expression into words and lists the next runs in your time zone. The subnet calculator gives you the network, mask, broadcast and host range of an IPv4 address, and the User-Agent parser tells you which browser, OS and device a string copied from a log claims to be, and whether it looks like a bot.
All 5 tools
- HTTP status codesEvery HTTP status code from 100 to 511, with its official name, what it means, when to use it and the RFC that defines it. Search by number or word.
- Cron expression explainerTurn a cron expression into plain words and list its next run times in your time zone, with daylight saving changes handled like Unix cron.
- User-Agent parserPaste a User-Agent and see the browser, engine, operating system, device and CPU it reports, whether it looks like a bot, and your Client Hints.
- Semver range checkerCheck which versions satisfy an npm semver range (^, ~, x, hyphens and ||), with the range explained in words and the highest matching version.
- CIDR calculatorWork out the network, mask, broadcast, host range and usable addresses of an IPv4 subnet in CIDR or mask notation, and whether the IP is private or public.