I Built 16 Free Dev Tools That Never Touch Your Data — Here's How

Tanu Mukherjee — Sun, 24 May 2026 15:13:09 +0000

Tags: webdev, javascript, opensource, productivity

The Problem

Every developer uses online tools daily. Format some JSON. Test a regex. Decode a JWT. Compare a diff.

But most online tool sites have a dirty secret: they upload your data to their servers. That JWT token you just pasted? It's been logged. That JSON with API keys? Stored somewhere.

On top of that, they're slow, covered in pop-ups, and half of them require sign-ups to do basic things.

What I Built

DevToolBox — 16 developer tools that run entirely in your browser. No backend server. No uploads. No sign-up. No tracking.

Live site: devtoolboxes.net

Open source: github.com/tanumuki/dev_tool_box

The Full Tool List

Category	Tools
Developer	JSON Explorer, Diff Checker, Regex Playground, Cron Visualizer, JWT Decoder, Markdown Preview
Encoding	Base64 Encoder/Decoder, URL Encoder/Decoder, Hash Generator
Files	PDF Tools (merge/split/compress/rotate/watermark), Image Compressor
Design	CSS Generators, Color Palette, OG Preview, QR Generator
Utility	Timestamp Converter

The "Zero Upload" Guarantee

Don't take my word for it. Open any tool, open your browser's Network tab, and use it. You'll see zero outbound requests. Everything processes in JavaScript on your machine.

Technical Decisions

Framework: Next.js with static export. Every page is prerendered at build time and served via Vercel's CDN. No server-side rendering needed since there's no dynamic data.

PDF Tools: Uses pdf-lib which runs entirely in the browser. Merge, split, compress, rotate, and watermark — all client-side.

Hash Generator: SHA-1, SHA-256, SHA-384, SHA-512 use the Web Crypto API (crypto.subtle.digest). MD5 required a custom JavaScript implementation since the Web Crypto API doesn't support it.

JWT Decoder: Just atob() and JSON.parse(). No jsonwebtoken dependency needed for decoding (verification requires the secret key, which is a server-side concern).

Markdown Preview: Built a custom parser using regex. No marked, no remark, no react-markdown. Handles headings, bold, italic, code blocks, lists, links, images, blockquotes, and horizontal rules.

Styling: Tailwind CSS with a dark theme. Glass-card components with backdrop blur. Gradient accents.

SEO Strategy

Each tool page has:

JSON-LD structured data (WebApplication + FAQPage + BreadcrumbList schemas)
4-5 FAQ entries targeting real search queries (e.g., "How do I decode a JWT token?")
Related tools section for internal linking
Optimized meta descriptions with canonical URLs

The homepage has Organization and WebSite schemas with a SearchAction for Google's sitelinks searchbox.

Total: 20 pages in the sitemap, all statically generated.

What's Next

Adding a blog with SEO articles targeting high-volume developer queries
More tools based on community feedback
Possibly Carbon Ads as an AdSense alternative (better CPM for developer audiences)

Try It

Site: devtoolboxes.net
Source: github.com/tanumuki/dev_tool_box

What tools would you want added? Let me know in the comments.

DEV Community: Tanu Mukherjee