15 Free Developer Tools You Should Bookmark Right Now

Why Browser-Based Developer Tools Win

Server-side developer tools require you to paste API keys, JWT tokens, database credentials, and sensitive strings into someone else's server. This is a security antipattern. Browser-based tools run your sensitive data through JavaScript locally — the server never sees your inputs.

Modern browser JavaScript is fast enough for virtually every developer tool use case. Regex testing, hash generation, JSON formatting, JWT decoding, cron expression building — these are pure computational tasks that don't need network connectivity after the page loads.

1. JWT Decoder — Stop Copying Tokens into jwt.io

JSON Web Tokens are base64-encoded strings containing authentication claims. Every time you copy a production JWT token into jwt.io, you're sending potentially valid authentication credentials to a third-party server. Our JWT Decoder decodes and validates tokens entirely locally — header, payload, expiry status, and algorithm badge, all processed in your browser.

Use case: debugging authentication issues, checking token expiry, verifying claims in API responses. Works instantly with any JWT regardless of the signing algorithm (HS256, RS256, etc.) — just decoding, not verification.

2. Cron Expression Builder — Stop Guessing Cron Syntax

Cron expressions are notoriously cryptic. '0 9 */2 * 1-5' — what does that mean? Our visual Cron Builder explains every expression in plain English, shows the next 10 scheduled run times, and generates platform-specific syntax for Linux crontab, GitHub Actions, and node-cron.

• Supports standard 5-field cron (min, hour, day, month, weekday)
• Real-time plain-English explanation
• Next 10 run times calculated instantly
• Copy syntax for Linux, GitHub Actions, and Node.js

3. Hash Generator — SHA-256, MD5, SHA-512 Instantly

Generating checksums, verifying file integrity, hashing passwords for comparison — hash generation is a daily developer task. Our Hash Generator computes MD5 (via pure JS implementation), SHA-1, SHA-256, and SHA-512 simultaneously using the Web Crypto API. All four hashes from a single text input, copy-ready.

Security note: MD5 and SHA-1 are deprecated for cryptographic security. Use SHA-256 or SHA-512 for any security-sensitive application. MD5 is still useful for non-security checksums and cache-busting keys.

4. Number Base Converter — Binary, Hex, Octal in One Place

Converting between decimal, binary, hexadecimal, and octal is something every systems programmer and embedded developer does regularly. Type in any field and all other bases update instantly. Includes visual bit analysis showing exactly which bits are set — invaluable for bitmasking and flag operations.

Also includes Base64 conversion in the same interface — useful for understanding how binary data is encoded for API payloads.

5–15. The Complete Developer Toolkit

All of the above are available for free at SiteConversor.com. No account required. No rate limits. No watermarks. Processing is 100% local in your browser.

• JSON Formatter & Validator — prettify API responses, catch syntax errors with precise line numbers
• Regex Tester — live match highlighting, all JS flags, individual match listing
• Base64 Encoder/Decoder — encode text and binary data, URL-safe mode for JWTs and query params
• URL Encoder/Decoder — encode special characters, decode percent-encoded URLs
• UUID/ULID Generator — v4 and v1 UUIDs, ULIDs, bulk generation up to 100, format options
• Meta Tag Generator — generate complete SEO, Open Graph, and Twitter Card tags
• Markdown to HTML — preview rendered output, export clean HTML
• Word Count — characters, words, sentences, reading time — useful for writing content within limits
• Password Generator — cryptographically random, configurable complexity
• SVG to PNG — convert vector graphics to raster at any resolution
• Cron Builder — visual editor with presets for the most common schedules