Developer tools guide: JSON, Base64, regex, JWT and more
AltFTool's Developer category has free in-browser utilities for everyday coding jobs: JSON Formatter, JWT Decoder, Regex Tester, Base64 and URL encoders, UUID Generator, Cron Expression Generator, SQL Formatter and Diff Checker. Most process input locally, so tokens and payloads are not uploaded.
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The everyday developer toolkit
The Developer category holds hundreds of utilities. These are the ones that cover most daily tasks:
- JSON Formatter: pretty-print and validate JSON, and preview what a GET, POST-form or POST-JSON request would look like.
- JWT Decoder: read a token's header and payload, see each claim's type, and check exp and iat in your local time.
- Regex Tester: live match highlighting, capture groups and positions using your browser's JavaScript RegExp engine.
- Text to Base64 and URL Encoder/Decoder: encode and decode strings, and dump a query string to JSON.
- UUID Generator: up to 100 v4 or v1 UUIDs at once, copied or downloaded as text.
- Cron Expression Generator: build a five-field cron string with a plain-English reading and the next five run times.
- SQL Formatter, YAML to JSON and JSON to TypeScript for reshaping data and code.
- Diff Checker: side-by-side comparison with additions, deletions and a similarity score.
- Unix Timestamp Converter: epoch seconds or milliseconds to local time, UTC and ISO 8601, and back.
Example: debug an API response
A common sequence when an API call returns something unexpected:
Format the body
Paste the raw response into the JSON Formatter. If it will not parse, the panel shows the parser's own error message, which usually reveals trailing commas, single quotes or other JavaScript-only syntax.
Inspect the auth token
Paste the bearer token into the JWT Decoder and check whether exp is already in the past or the audience claim is wrong.
Check timestamps
Convert any epoch values with the Unix Timestamp Converter to confirm they are in seconds rather than milliseconds.
Compare with a working response
Paste a known-good response and the broken one into the Diff Checker to spot the changed field.
Working safely with secrets
The tools listed above run in your browser, so pasting a token or payload does not send it to AltFTool. Even so, treat production secrets with care: prefer test tokens, and close the tab when done.
Going further
For network and domain checks, see the Security & Privacy category and the AltF DomainOps workspace. The AltF API & Widgets product documents AltFTool's public read APIs. Search shorthand helps here too: typing 'dev' or 'code' in site search expands to developer, JSON, HTML, CSS, SQL and regex tools.
Tools used in this guide
- JSON FormattingRegular formatted display of JSON, plus automatic formatting/conversion for API interface testing (GET, POST, POST-JSON).
- JWT DecoderDecode JWT header and payload claims instantly in the browser.
- Regex TesterTest and validate regular expressions instantly with live results.
- Text to Base64Encode text into Base64 and decode Base64 locally.
- Cron Expression GeneratorBuild cron expressions with readable schedule previews.
- Diff CheckerCompare two files and highlight the differences
Frequently asked questions
Is it safe to paste a JWT into an online decoder?
AltFTool's JWT Decoder runs entirely in your browser and does not upload the token. Still, avoid pasting live production tokens anywhere you do not need to.
Which regex flavour does the Regex Tester use?
It uses your browser's built-in JavaScript (ECMAScript) RegExp engine, so results match what your JavaScript code will do.
Does the JSON Formatter send requests to my API?
No. Its request panels build and display what the request would look like, but nothing is sent. Copy the payload into your own HTTP client to run it.