The Best Free Developer Tools Available Online Right Now
Developers are always looking for faster ways to debug, format, test, and convert. Online tools have eliminated the need to install local software for most day-to-day tasks. Here's a roundup of the most useful free online developer tools — all available at Toolzie.ca.
JSON Tools: Format, Validate, and Edit
JSON is the universal data format for APIs and configuration files. A good online JSON tool lets you:
- Format/pretty-print minified JSON for human reading
- Validate JSON syntax and spot errors instantly
- Convert JSON to TypeScript interfaces, YAML, or CSV
- Edit JSON in a tree view instead of raw text
The Toolzie JSON Editor handles all of these and shows live validation as you type.
Regex Tester
Regular expressions are powerful but notoriously hard to write correctly. An online regex tester with live highlighting shows you exactly what your pattern matches — in real time, as you type.
Good regex testers support multiple flavours (JavaScript, Python, PHP), show capture groups, and let you test against multiple strings simultaneously. Try it here.
JWT Decoder
JSON Web Tokens (JWTs) are base64-encoded by design but not always readable at a glance. An online JWT decoder breaks the token into its three parts — header, payload, and signature — and shows the decoded content instantly.
This is invaluable for debugging authentication issues in APIs. Decode a JWT here.
Base64 Encoder/Decoder
Base64 encoding turns binary data into ASCII text for safe transmission. You'll encounter it constantly in API responses, email attachments, and authentication tokens. An online encoder/decoder converts in both directions instantly. Use it here.
CSS Tools
Modern CSS development benefits from several dedicated tools:
- CSS Box Shadow Generator — visually design shadows with a live preview
- Gradient Generator — create CSS gradients visually with colour stops
- CSS Unit Converter — convert between px, rem, em, vh, vw
Cron Expression Builder
Cron expressions are powerful but cryptic. 0 9 * * 1-5 means 'every weekday at 9am' — but few people can write that from memory. A visual cron builder lets you set the schedule in plain English and generates the expression for you.
SQL Tools
For database work, a browser-based SQL editor and SQL formatter are essential. Format messy SQL queries into readable, properly indented code without any local setup.
Frequently Asked Questions
Are online developer tools safe to use with sensitive data?
Be cautious with any sensitive data (API keys, production database credentials, personal user data). Choose tools that process data client-side (in your browser) rather than uploading to a server. All Toolzie developer tools process data locally in your browser.
Can I use these tools offline?
Browser-based tools typically require an internet connection to load, but once loaded, most process data locally. Some tools can be saved as bookmarks and used partially offline if cached by the browser.
What is the difference between a JSON formatter and a JSON editor?
A formatter just pretty-prints existing JSON. An editor provides an interactive interface to view, navigate, and modify the JSON structure — including tree view, add/remove keys, and type validation.
Is there a free alternative to Postman for API testing?
For simple API testing, browser-based tools cover many use cases. For full API testing (sending requests, viewing responses), Postman has a free tier, as does Insomnia. For quick HTTP header checking, a browser-based HTTP header viewer works well.
Try the JSON Editor
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