Developer tools should be fast and frictionless. The last thing you want when debugging a JWT or formatting a JSON response is to create an account, verify your email, and navigate a dashboard. Here are 10 free browser-based dev tools that are ready the moment you open them.
1. JSON Formatter
Paste any JSON and instantly get a beautifully formatted, syntax-highlighted result. Detects errors with exact line numbers so you can fix malformed JSON fast. Essential for working with API responses, config files, and schema markup.
- Validates JSON and highlights syntax errors with line numbers
- Beautify or minify with one click
- Supports large JSON files without performance issues
2. JWT Decoder
Decode any JSON Web Token instantly — inspect the header, payload, and signature without needing the secret key. Useful for debugging auth flows, checking token expiry, and verifying claims during development.
Privacy note: The JWT Decoder processes tokens entirely in your browser. Your token is never sent to any server — safe to use with real tokens during development.
3. Base64 Encoder / Decoder
Encode strings and files to Base64 or decode Base64 back to plain text. Used constantly in web development for encoding images in CSS data URIs, HTTP Basic Auth headers, and API payloads.
4. URL Encoder / Decoder
Encode special characters for safe use in URLs, or decode percent-encoded strings back to readable text. Critical for building query strings, canonical tags, hreflang attributes, and UTM parameters correctly.
5. UUID Generator
Generate RFC 4122 compliant v4 UUIDs in bulk. Copy a single UUID or generate a list of 10, 50, or 100 at once. Useful for database primary keys, API request IDs, and test data generation.
6. Regex Tester
Test regular expressions with live match highlighting as you type. Supports flags (global, case-insensitive, multiline), shows match groups, and highlights all matches in the test string. Saves hours of trial-and-error in your IDE.
7. CSS & JS Minifiers
Reduce CSS and JavaScript file sizes by 20–40% instantly. Removes whitespace, comments, and redundant code. Run it before deploying to improve page load speed and Core Web Vitals scores — no build tool required.
8. Cron Expression Generator
Build cron schedules visually without memorizing the syntax. Select minute, hour, day, month, and weekday values and get the cron expression instantly. Includes a human-readable description so you can verify the schedule is correct before deploying.
9. SQL Formatter
Paste messy, minified or auto-generated SQL and get a clean, indented, readable query back. Supports SELECT, INSERT, UPDATE, DELETE, JOIN, and subqueries. Makes code reviews and debugging significantly easier.
10. DNS Lookup
Check DNS records for any domain — A, AAAA, CNAME, MX, TXT, NS and more. Useful for verifying domain configuration, debugging email delivery issues, and checking SSL certificate domains.
Frequently Asked Questions
What is the best free JSON formatter?
AllOmniTools JSON Formatter is a free browser-based tool that validates and beautifies JSON with syntax highlighting and line-number error detection. No account or upload required — open the page and paste your JSON.
Can I decode JWT tokens online safely?
Yes, if the tool processes the token locally in your browser. AllOmniTools JWT Decoder decodes tokens client-side — your token is never sent to any server. Safe to use with real tokens during development.
What is Base64 encoding used for?
Base64 encoding represents binary data as ASCII text. Common uses include encoding images in CSS data URIs, encoding credentials in HTTP Basic Auth headers, and encoding binary data in JSON APIs.
Do these tools work offline?
Yes, after the first page load. AllOmniTools is a Progressive Web App with a service worker that caches tools locally. Once loaded, they work without an internet connection.
Browse all dev tools: allomnitools.com/dev-tools/ — 20+ free developer utilities, no account required.