Developer Utilities

Developer utilities are the small, single-purpose tools you reach for in the middle of real work: reading a token, planning a subnet, converting a timestamp, testing a regular expression or checking a cron schedule. Every tool on this hub runs entirely in your browser, so the token, address plan or log line you paste is never sent to a server. That matters, because the inputs are often real credentials and production data.

What the tools are really computing

• A JWT is readable by anyone. It is three base64url-encoded segments, a header, a payload and a signature, joined by dots. Decoding shows the claims but proves nothing about whether the token is genuine; only verifying the signature with the right key does that, and that check belongs on the server.
• Unix time counts seconds since 1970-01-01 UTC. A JWT’s exp and iat claims use seconds, while many JavaScript APIs use milliseconds, and mixing the two is a classic expiry bug.
• A CIDR block is bit arithmetic. In 10.0.0.0/24 the first 24 bits name the network and the remaining 8 address hosts: 256 addresses, 254 usable in classic networking. Cloud providers reserve more; AWS keeps five addresses in every subnet.
• Identifiers trade randomness for order. A version 4 UUID carries 122 random bits. A ULID puts a millisecond timestamp first, so IDs sort by creation time and insert more neatly into database indexes.
• Cron has five fields, minute, hour, day of month, month and day of week, evaluated in the timezone of whatever runs the schedule, which on servers is often UTC.

How the formats fit together

Most of this hub is tools, built to be bookmarked and used in seconds. The one handbook, on OAuth and authentication, explains where the tokens you decode come from: authorization codes, PKCE, scopes and the difference between an ID token and an access token. A few tools sit on the boundary with other hubs: the backoff calculator sizes retries, the cosine similarity calculator shows how embedding search measures closeness, and the sampling simulator reshapes a model’s next-token probabilities.

Common mistakes

• Trusting a decoded JWT without verifying its signature, or accepting tokens that declare alg: none.
• Pasting real secrets into online tools that send input to a server.
• Writing a regular expression with nested quantifiers such as (a+)+, which can backtrack catastrophically on hostile input.
• Restricting both day-of-month and day-of-week in a cron expression and expecting both to apply; standard cron runs the job when either one matches.
• Running chmod 777 to fix a permission error instead of granting the one permission that was missing.