Developer Guides
Plain-language guides on JSON, JWT, regex, timestamps and more - written by developers for developers.
20 guides
JSON
How to Format JSON: Readable Output in the Browser, Editor or Terminal
Format minified JSON for readability with an online formatter, an editor shortcut, or a command-line tool like jq or python -m json.tool.
7 min read
How to Validate JSON: Find the Exact Line and Column of a Syntax Error
Validate JSON syntax with the online validator, JSON.parse in JavaScript or json.loads in Python, and diagnose the most common parse errors.
7 min read
JSON Syntax Guide: The Six Value Types and the Rules That Catch You
A complete walkthrough of JSON syntax: objects, arrays, strings, numbers, booleans and null, plus the edge cases that break real documents.
8 min read
JSON vs YAML: Which Format Should You Use, and How Do You Convert?
JSON for data crossing system boundaries, YAML for configuration humans write. Compare syntax, footguns and how to convert between them losslessly.
8 min read
Common JSON Errors: The Five Mistakes That Break Every Parse
The short list of JSON parse failures - trailing commas, unquoted keys, missing commas, comments and unbalanced braces - with symptom, cause and fix.
8 min read
JWT
What Is a JWT? How JSON Web Tokens Work
A JSON Web Token (JWT) is a compact, signed token of three base64url parts: header, payload and signature. Learn why it is not encryption.
8 min read
How to Decode a JWT: Read the Header and Payload Without a Secret
Decode any JWT by splitting on the dots and base64url-decoding the header and payload. No secret is needed, because decoding is not signature verification.
8 min read
JWT Header Explained: alg, typ and kid
The JWT header is the first base64url segment and declares the signing algorithm. Learn what alg, typ and kid mean and why alg=none is a known attack vector.
7 min read
JWT Payload Explained: Claims Like sub, iss, aud and exp
The JWT payload holds the claims: sub, iss, aud, exp, nbf, iat and jti. Learn what each registered claim means and why the payload is readable by anyone.
7 min read
JWT Expiration Explained: exp, iat, nbf and Refresh Tokens
The exp claim sets when a JWT stops being valid. Learn how exp, iat and nbf work, how servers enforce expiry and how refresh tokens extend a session.
8 min read
Regex
Regular Expressions Guide: How Regex Works with Examples
Learn regular expressions from scratch: literals, metacharacters, character classes, quantifiers, anchors, groups and flags, with examples you can test online.
10 min read
Regex Cheat Sheet: Every Metacharacter Explained
A compact regex cheat sheet: anchors, character classes, quantifiers, groups, alternation and flags, with the meaning and an example for every common token.
8 min read
Email Regex: How to Validate an Email Address
A practical email regex, why the full RFC 5322 pattern is a trap, and how to validate email in HTML5, JavaScript and Python without over-engineering.
7 min read
URL Regex: How to Match and Validate a URL
Match and validate URLs with regex: protocol, host, path, query and fragment, plus practical patterns and when to use the URL API instead of a regex.
7 min read
Regex Groups and Capturing: How Grouping Works
Capturing groups, non-capturing groups, named groups and backreferences: what parentheses do in regex and how to extract pieces of a match.
8 min read
Time & Date
Unix Timestamp Guide: Convert and Read Epoch Time
A Unix timestamp is the number of seconds since 1970-01-01 UTC. Convert one in the tool or in code, and understand the 2038 limit on 32-bit systems.
8 min read
Epoch Time Explained: The Epoch, UTC and the Year 2038 Problem
Epoch time counts seconds since 1970-01-01 00:00:00 UTC. Learn why the epoch exists, why it is timezone-free, and how the 2038 problem works.
7 min read
ISO 8601 Date Format Explained: What It Looks Like and How to Use It
ISO 8601 is the international date and time format, written like 2026-08-15T14:30:00Z. Learn how to read it, why the order matters and which form to store.
8 min read