Guides
Longer explanations for the jobs the Fieldkit tools do in one click. Each guide is paired with a tool, and its examples show real inputs with the exact output that tool produces.
Regular expressions in JavaScript: a working guide
Classes, flags, greedy vs lazy, anchors, lookbehind and the patterns that freeze a tab.
Read guide → GUIDE · TIMESTAMPUnix timestamps: seconds, milliseconds, time zones and 2038
Seconds vs milliseconds, offsets in ISO 8601, JavaScript date parsing and the 2038 limit.
Read guide → GUIDE · BASE64Base64 explained: padding, base64url, size and common mistakes
Padding, the URL-safe alphabet, the 33% size cost and how to read a JWT payload.
Read guide → GUIDE · JSONConverting JSON to CSV without losing data
Uneven keys, nested objects, arrays, quoting, big numbers and spreadsheet traps.
Read guide → GUIDE · JSONPretty-print JSON without breaking it
Parse first, then format. Trailing commas, duplicate keys, big integers and key order.
Read guide → GUIDE · CRONCron expressions in practice
Field order, steps and ranges, the day-of-month OR rule, time zones and DST.
Read guide →How these guides are written
The tools answer "what is the output?". The guides answer "why is it that, and what can go wrong?". They focus on the mistakes that show up in real logs, configs and spreadsheets: a timestamp read in the wrong unit, a cron line that fires on the wrong days, a regex that accepts a lookalike domain, a CSV that loses digits.
Technical claims are checked against the primary sources where one exists: the RFCs for JSON (8259), CSV (4180), Base64 (4648) and date-time strings (3339), the POSIX definition of epoch time, the ECMAScript specification for JavaScript dates and regular expressions, and the crontab(5) manual page. Every example input was run through the same code the matching tool uses, and the output shown is the output it produced.
Each guide shows the date it was last updated. If you spot an error, the Contact page has the email address; please include the section and the source you are relying on.
Guides by tool
- Regex Tester: Regex in JavaScript
- Timestamp Converter: Unix timestamps
- Base64 Encoder & Decoder: Base64 explained
- JSON to CSV Converter: JSON to CSV
- JSON Formatter & Validator: Pretty-print JSON
- Cron Expression Generator: Cron expressions
The UUID Generator, URL Encoder and Color Converter do not have a dedicated guide yet. Their tool pages carry their own worked examples.