I Built 15 Free Browser-Based Developer Tools — Here's What I Learned

ARUN GOPAL — Thu, 09 Apr 2026 20:08:08 +0000

Every developer has that moment: you need to quickly format some JSON, generate a UUID, or encode a string to Base64. You google it, click the first result, and get hit with cookie banners, newsletter popups, and a loading spinner while 3MB of JavaScript downloads to do something that takes 5 lines of code.

I decided to fix this by building ToolPry — a collection of 15 developer tools that are fast, private, and free.

The Rules I Set for Myself

Every tool must run 100% in the browser. No server calls. No APIs. Your data never leaves your machine.
No frameworks. Each tool is a single HTML file with inline CSS and JS. No React, no Tailwind, no build step.
No tracking. No Google Analytics, no Hotjar, no cookies (except for ads).
No sign-up. Every tool is fully functional for everyone, immediately.
Must work offline. Service worker caches everything after first visit.

The 15 Tools

Here's what I built:

Data & Encoding

JSON Formatter & Validator — Format, validate, minify with syntax highlighting. Uses native JSON.parse() / JSON.stringify().
Base64 Encoder/Decoder — Full UTF-8 support via btoa(unescape(encodeURIComponent())).
URL Encoder/Decoder — Both encodeURI and encodeURIComponent modes.
HTML Entity Encoder — Prevents XSS by encoding <, >, &, ", '.

Security

Password Generator — Uses crypto.getRandomValues() (the same CSPRNG banks use). Customizable length, character types, bulk generation.
Hash Generator — MD5 (JS implementation), SHA-1, SHA-256, SHA-512 (via Web Crypto API crypto.subtle.digest()).

Generators

UUID Generator — RFC 4122 v4 UUIDs using crypto.getRandomValues. Bulk generate up to 100.
Lorem Ipsum Generator — Paragraphs, sentences, or word count. Classic or random start.
QR Code Generator — Uses qrcodejs library. Configurable size and error correction. Download as PNG.

Text & Writing

Word & Character Counter — Words, characters, sentences, paragraphs, reading time (238 WPM), speaking time, keyword density, vocabulary richness.
Markdown Preview — Live rendering using marked.js, sanitized with DOMPurify to prevent XSS.

Developer Utilities

Regex Tester — Real-time match highlighting with flag toggles (g, i, m, s). Shows match groups and indices.
Color Converter — Hex ↔ RGB ↔ HSL with live preview, native color picker, and random generator.
Timestamp Converter — Unix epoch ↔ human dates. Auto-detects seconds vs milliseconds. Live clock.
CSS Gradient Generator — Linear/radial, 3 color stops, adjustable angle, one-click CSS copy.

Technical Decisions

Why no framework? Each tool is self-contained. A JSON formatter doesn't need React's virtual DOM — it needs JSON.parse() and a <pre> tag. Keeping things vanilla means each page is 6-15KB total, loads instantly, and has zero dependencies to maintain.

Why Web Crypto API? For the password generator and hash generator, I use the browser's built-in cryptographic functions. crypto.getRandomValues() provides the same quality of randomness used in TLS connections. For SHA hashing, crypto.subtle.digest() is faster and more secure than any JavaScript implementation.

Why DOMPurify on Markdown? The Markdown preview renders user input as HTML. Without sanitization, a user could inject malicious scripts via Markdown. DOMPurify strips any XSS vectors before the HTML reaches the DOM.

What's Next

I'm planning to add:

JWT Decoder
Diff Checker (text comparison)
CSV to JSON converter
DNS Lookup tool
Cron Expression Parser

Try It

The site is at toolpry.com.

What developer tools do you find yourself reaching for most often? I'd love suggestions for what to build next.

Built with vanilla HTML/JS. Hosted on Cloudflare Pages (free tier). Total monthly cost: one domain name.

DEV Community: ARUN GOPAL