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Guides
The reasoning behind the tools. Each guide explains one concept well enough that you can defend the decision in a code review.
These guides exist because a tool that shows you a ratio or a field breakdown is more useful when you understand why the rule is what it is. Each one covers a single idea — the ones that come up in code reviews, in incident write-ups and in the arguments that take an afternoon to settle.
They are written by Enrique M., they are checked against the specification or the implementation they describe, and every tool they mention runs in your browser.
How to Read a JSON Web Token (JWT) 6 min read · A practical guide to reading a JSON Web Token: what the header and payload… Twelve Regular Expressions Worth Knowing by Heart 8 min read · Twelve regular expressions for the tasks that come up in every project… Cron Expressions: A Cheat Sheet and Its Traps 7 min read · The five fields of a Unix cron expression, the day-of-month and day-of-week… UTC vs Local Time: The Bugs It Causes 6 min read · Why storing local time is a bug waiting to happen, how daylight saving breaks… WCAG Contrast Ratios for Developers 5 min read · What the contrast requirements actually are, which ones apply to your UI, and… Handling Environment Variables Safely 6 min read · How to keep credentials out of version control and out of your shell history… A Naming Convention for UTM Parameters 5 min read · How to pick UTM source, medium and campaign values that produce a readable… What a Useful Diff Looks Like 6 min read · Why line diffs are too coarse, when word-level highlighting helps, and how… Common JSON Errors and How to Fix Them 7 min read · The six JSON mistakes behind almost every parse error: trailing commas… Base64 Is Not Encryption 6 min read · What Base64 actually does, why it is not a security measure, when it is the… Cache-Control and ETag, Explained 9 min read · How HTTP caching works: what Cache-Control directives mean, what an ETag is… Designing API Error Responses 8 min read · What an API error body should contain, which status code to use, and how to… How Webhook Signature Verification Works 8 min read · How to verify that a webhook really came from the provider: HMAC signatures… Quoting and Escaping in Shell Commands 9 min read · Why unquoted variables break, the difference between single and double… UUIDs, ULIDs and Snowflake IDs 9 min read · How to choose an identifier: random UUIDv4, time-ordered UUIDv7, ULID… How SQL Injection Works, and How to Prevent It 9 min read · What SQL injection is, how string concatenation creates it, why parameterised…