25 Free Developer Tools That Run 100% in Your Browser
If you've ever pasted sensitive data into a random online tool and immediately regretted it — this post is for you.
I built toolsstack.cloud — a collection of 25 free developer tools that run entirely in your browser. No backend. No account. No data ever leaves your device.
Here's the full list, grouped by category.
🔐 Security & Auth
1. JWT Decoder
Decode and inspect JWT tokens instantly — header, payload, expiry, and signature status. Useful when debugging auth issues without needing Postman or curl.
2. Hash Generator
Generate MD5, SHA-1, SHA-256, and SHA-512 hashes from any text. Client-side using the Web Crypto API — nothing is sent to a server.
3. Password Generator
Cryptographically secure passwords with options for length, uppercase, numbers, symbols. Uses crypto.getRandomValues() — genuinely random, not Math.random().
📦 Data & Encoding
4. JSON Formatter & Validator
Format, minify, and validate JSON with syntax highlighting. Shows line numbers on errors. One of the most-used tools on the site.
5. YAML to JSON Converter
Paste YAML, get JSON. Or paste JSON, get YAML. Uses js-yaml — supports anchors, multiline strings, and nested objects. Great for switching between Kubernetes manifests and API calls.
6. JSON to CSV Converter
Convert JSON arrays to CSV with auto-detected column headers. Download the result directly. No server upload needed.
7. Base64 Encoder / Decoder
Encode and decode Base64 — supports both text and file input. Handles UTF-8 correctly (unlike some tools that break on non-ASCII characters).
8. Image to Base64
Upload an image, get a Base64 data URI. Copy it directly into your HTML <img src=""> or CSS background-image. Useful for embedding small icons without an extra HTTP request.
9. URL Encoder & Decoder
Encode/decode URLs with two modes: encodeURIComponent (for query params) and encodeURI (for full URLs). Also parses URLs into protocol, host, path, and individual query parameters.
10. HTML Entity Encoder
Encode special characters like <, >, &, " to HTML entities and back. Useful when embedding user-generated content or debugging XSS-safe output.
🛠️ Developer Utilities
11. UUID / GUID Generator
Generate UUID v4 identifiers — single or bulk up to 1000 at once. Options for uppercase, no hyphens, or {braces} GUID format. Uses crypto.getRandomValues() for proper randomness.
12. Regex Tester
Test regular expressions with live match highlighting, group capture display, and flags support. Faster than switching between your editor and a browser console.
13. Cron Expression Generator
Build cron schedules with a visual builder — minute, hour, day, month, weekday. Shows a human-readable description and the next 5 run times. No more googling "cron every 15 minutes".
14. Epoch / Unix Timestamp Converter
Convert between Unix timestamps and human-readable dates in any timezone. Also shows the current timestamp live — useful for debugging API responses with created_at fields.
15. Diff Checker
Paste two blocks of text and see line-by-line differences highlighted in green/red. Good for quickly spotting config file changes or API response differences.
16. chmod Calculator
Click checkboxes for owner/group/others read/write/execute permissions and see the numeric value update in real time. Never google "chmod 755 meaning" again.
💻 Code & Text
17. CSS Minifier
Minify CSS and see the exact bytes saved. Pure client-side — paste your stylesheet, get minified output without uploading to any server.
18. SQL Formatter
Format and beautify SQL queries with proper indentation and keyword casing. Supports SELECT, INSERT, UPDATE, DELETE, JOIN, subqueries.
19. Markdown Converter
Convert Markdown to HTML with a live preview. Useful for checking how your README or blog post will render before committing.
20. Lorem Ipsum Generator
Generate placeholder text — choose paragraphs, sentences, or word count. Starts with the classic "Lorem ipsum dolor sit amet" or generates fully random Latin-ish text.
🎨 Design & Visual
21. Color Converter
Convert between HEX, RGB, HSL, and HSV instantly with a color picker. Copy any format with one click. Useful when your designer gives you a hex code but your CSS needs HSL.
22. QR Code Generator
Generate QR codes for URLs, WiFi credentials, vCards, email, SMS, and more. Customize dot styles, eye shapes, colors, and upload a logo overlay. Download as PNG or SVG.
🌏 Specialized
23. IP Lookup
Shows your public IPv4 and IPv6 addresses with geolocation (country, city, ISP). Useful for verifying VPN connections or debugging network issues.
24. PDF Text Extractor
Extract text from PDF files — supports both English and Thai. Uses pdf.js entirely in the browser. The PDF never gets uploaded anywhere.
25. Thai Text to URL Slug
Convert Thai text to URL-friendly slugs using RTGS (Royal Thai General System of Transcription) romanization. For example, สวัสดีครับ → sawatdi-khrap. Useful for building SEO-friendly URLs for Thai-language content.
Why client-side only?
Most online developer tools send your data to a server. That means:
- Your JWT tokens (with user data) go to someone else's server
- Your passwords get logged somewhere
- Your internal API responses are stored in someone's database
Every tool on toolsstack.cloud processes data entirely in your browser using native browser APIs (crypto.getRandomValues, URL, FileReader) and trusted open-source CDN libraries like js-yaml and pdf.js.
The network tab stays clean.
Tech stack
Pure HTML + Vanilla JavaScript. No framework. No build step. No node_modules. The entire site is static files on shared hosting.
For tools that need libraries:
-
js-yaml@4.1.0— YAML parsing -
pdf.js@4.4— PDF text extraction -
qrcode-generator— QR code rendering
Everything else uses browser-native APIs.
If you find any of these useful — or want to suggest a tool that's missing — feel free to drop a comment below.
