The Best Free Online Developer Tools
Developers waste hours on repetitive tasks: formatting JSON by hand, manually encoding strings, memorizing regex syntax. These free online tools eliminate that friction. All available at RoughTools Developer Tools — no signup, no download, instant results.
1. JSON Formatter & Validator
Paste minified or malformed JSON and get beautifully formatted, syntax-highlighted output instantly. Validates JSON and shows exactly where errors are.
Use case: Reading API responses, debugging config files, formatting data for readability
2. Regex Tester
Write and test regular expressions with live match highlighting. Shows capture groups, matches, and replacements in real time. Supports JavaScript regex flags.
Use case: Validating email/phone patterns, writing form validation, parsing log files
3. Base64 Encoder / Decoder
Encode strings, files, or images to Base64 and decode Base64 back to readable text. Useful for embedding images in CSS, handling auth headers, and data URIs.
4. JWT Decoder
Paste a JSON Web Token and instantly see the header, payload, and signature — decoded and formatted. Useful for debugging authentication issues without touching the code.
Pro tip: A JWT is three Base64-encoded parts separated by dots. The middle part (payload) contains the claims — use the JWT decoder to verify what claims your server is actually sending.
5. UUID Generator
Generate RFC 4122 compliant UUIDs in v1 (time-based), v4 (random), and v5 (name-based) formats. Generate up to 1000 at once for bulk inserts.
6. Hash Generator
Generate MD5, SHA-1, SHA-256, and SHA-512 hashes from any string or file. Useful for file integrity checking and password hashing examples.
7. CSS Minifier
Minify CSS by removing whitespace, comments, and redundant rules. Reduces file size by 30–60% for most stylesheets.
8. Diff Checker
Paste two blocks of text and see exactly what changed, line by line. Highlights additions in green and deletions in red. Useful for comparing configs, API responses, or code snippets.
9. Timestamp Converter
Convert Unix timestamps to human-readable dates and vice versa. Supports milliseconds and seconds. Shows the date in multiple time zones.
10. Cron Expression Parser
Paste a cron expression and get a plain-English description of when it runs, plus the next 5 scheduled execution times. Invaluable for setting up and debugging cron jobs.
Honorable Mentions
- SQL Formatter — Format messy SQL queries with proper indentation
- YAML Validator — Validate and convert YAML to JSON
- Markdown Editor — Live preview Markdown editor with export
- Chmod Calculator — Build Unix file permissions visually
Why Free Online Tools vs. Installing Software?
- No installation: Works on any machine, including locked-down corporate laptops
- No context switching: Open a browser tab, use the tool, close it
- Always up to date: No version mismatches
- Works on mobile: Review a JWT or check a regex from your phone