Every developer has a collection of bookmarklets and random websites they use for quick utilities: format some JSON, diff two configs, generate a UUID, encode something in base64.
Most of these tools send your data to a server. I built 10 developer utility tools that never leave your browser.
The Stack (or Lack Thereof)
Each tool is one HTML file. No React, no Vue, no build step. Vanilla JS + browser APIs:
crypto.getRandomValues() for UUIDs, random numbers, secure passwords
Canvas API for QR code rendering
localStorage for saving preferences (with try-catch guards)
LCS algorithm for text diffing
GitHub-Flavored Markdown parser (regex-based, not a library)
Hosting: GitHub Pages (free, global CDN). No server-side code. No database.
The 10 Tools
1. JSON Formatter & CSV Converter
Format, validate, minify JSON. Convert between JSON and CSV with smart type inference. Handles nested objects and big integers.
3. Base64 Encoder & Decoder
Encode/decode text and files to/from Base64. Also includes hex and binary modes. File drag-and-drop support.
5. Password Generator
crypto.getRandomValues() for secure randomness. Configurable length (8-128 chars), character sets, ambiguous character exclusion. Full entropy — no Math.random() shortcuts.
7. Markdown Editor
Split-pane editor with live preview. GitHub-Flavored Markdown (tables, strikethrough, code blocks). Copy HTML or download.
9. Timestamp Converter
Human-readable dates to Unix timestamps (seconds and milliseconds) and vice versa. Timezone-aware ISO 8601 support. Relative time display.
Bonus: Quick Reference Tools
Case Converter — UPPER, lower, Title, Sentence, camelCase, snake_case, kebab-case
Word Counter — Words, characters, sentences, paragraphs, reading time
Random Generator — Numbers, coin flips, dice rolls, list picker, shuffle (crypto.getRandomValues)
HTML Formatter & CSS Minifier — Tag-aware HTML indentation, CSS whitespace stripping
Color Picker — HEX/RGB/HSL converter with EyeDropper API support
Why Browser-Native?
Security. Your JSON payloads, API keys, and configuration files never leave your device.
Offline. All tools work without internet after first load. Service workers cache everything.
Speed. No network round-trip. Type a UUID, get it instantly. Diff two files, see results immediately.
Auditable. View source to confirm: no telemetry, no analytics, no hidden API calls.
Free vs PRO
Every tool works fully for free with reasonable limits. The PRO Bundle ($19.99 one-time) removes all limits across all tools with a single license key.
Part of | 5 Image Tools
SOCIAL SHARE CARD GENERATOR