Developer tool guides

The jobs people reach for a website to do, and why doing them on your own machine is usually the better answer.

• How to decode a JWT without pasting it into a website

  A JSON Web Token is a bearer credential: whoever holds it can act as you until it expires. Pasting one into a web decoder hands that credential to a third party.

• A JSON formatter for Mac that leaves your key order alone

  Most online formatters silently reorder your keys and re-encode your strings. On a config file or an API response you are about to diff, that is not a formatting change — it is a content change.

• Encode and decode Base64 on a Mac

  Base64 is an encoding, not encryption. Anything encoded in it is readable by anyone who bothers, which is exactly why it should not be handed to a website.

• A regex tester that reports named groups by name

  A green tick tells you the pattern matched something. It does not tell you what, where, or whether the group you care about captured what you think.

• Compare two blocks of text on a Mac

  Two config files that look identical usually differ by something invisible — a tab against four spaces, a trailing space, or a line ending from another operating system.

• Convert a Unix timestamp to a date

  1700000000 is a moment in November 2023. Nobody reads that at a glance, which is why the conversion is one of the most-searched developer tasks there is.

• Generate SHA-256 and MD5 hashes on a Mac

  A hash generator that runs on a website is asking you to send it the thing you are hashing. That is often a password, a token, or a file you are checking precisely because you do not trust its origin.

• Generate a UUID on a Mac

  A UUID from a website is generated on someone else's machine, which is a strange place to source an identifier you are about to treat as unique and unguessable.

• Work out a subnet from CIDR notation

  192.168.1.10/24 contains everything you need to know about the network — but only after arithmetic that nobody should be doing mentally at the point they need the answer.

• Read and write a cron expression

  Five fields with no labels, and one of them counts from a different starting number than the rest. Cron is read wrongly more often than almost any other syntax in common use.