Developer Guides & Tutorials
Practical guides on JSON, regex, encoding, networking and text handling, each linked to a free browser tool you can use right away.
Each article explains one problem in plain terms, such as why a parser rejects your JSON or what a regular expression actually matches, and links to the tool that lets you try it. Like the tools themselves, every example runs in your browser, so nothing you paste is uploaded.
- How to Decode a JWT Without Trusting ItA JWT is readable by anyone, so decoding proves nothing. See its three parts, the claims worth reading, and what verification must check before you trust it.
- CIDR Notation and Subnetting ExplainedWhat /24 and /26 mean, how to find the network address, broadcast address and usable hosts, with a full CIDR table and a worked IPv4 subnetting example.
- Cron Expression Cheat Sheet With ExamplesRead and write cron expressions: the five fields, the special characters, and copy-paste schedules for every 5 minutes, weekdays at 9am, monthly jobs and more.
- Unix Timestamps: Seconds, Milliseconds, 2038A Unix timestamp counts time since 1970-01-01 UTC. Tell seconds from milliseconds, convert to dates, avoid time zone bugs and understand the 2038 limit.
- UUID v4 vs v7: Which Should You UseUUID v4 is fully random; UUID v7 starts with a timestamp so it sorts by creation time. Compare them for database keys, privacy and what each one reveals.
- Base64 vs Base64URL: What Is the DifferenceBase64 and Base64URL use two different characters and padding rules. Learn when each is correct, why URLs and JWTs need the URL-safe form, and how to convert.
- Fix JSON Unexpected Token ErrorsWhy JSON.parse throws "Unexpected token" or "Unexpected end of JSON input", the six usual causes, and how to find the exact character that breaks it.
- Regex Cheat Sheet for JavaScriptA compact reference for JavaScript regular expressions: character classes, quantifiers, anchors, groups, lookarounds and flags, with examples you can test live.