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.

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2. Text Diff Checker

Compare two texts side by side. Line-by-line and character-level diff using Longest Common Subsequence algorithm. Highlights insertions and deletions.

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3. Base64 Encoder & Decoder

Encode/decode text and files to/from Base64. Also includes hex and binary modes. File drag-and-drop support.

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4. UUID Generator

Generate UUID v4 (random) and v7 (time-ordered). Batch up to 100 at once. Uses crypto.getRandomValues() for true randomness.

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5. Password Generator

crypto.getRandomValues() for secure randomness. Configurable length (8-128 chars), character sets, ambiguous character exclusion. Full entropy — no Math.random() shortcuts.

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6. QR Code Generator

Generate QR codes for URLs, WiFi networks, email, SMS, and vCard contacts. Wraps qrcodejs library. Download as PNG.

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7. Markdown Editor

Split-pane editor with live preview. GitHub-Flavored Markdown (tables, strikethrough, code blocks). Copy HTML or download.

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8. URL Encoder & Decoder

Full URL and component encoding. Data URL generation. Handles edge cases like nested encoding and special characters.

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9. Timestamp Converter

Human-readable dates to Unix timestamps (seconds and milliseconds) and vice versa. Timezone-aware ISO 8601 support. Relative time display.

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10. Number Base Converter

Binary, octal, decimal, hexadecimal. Fractional number support. Step-by-step conversion mode for learning.

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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.

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Part of 24 free browser tools — all client-side, no signup, no tracking.

Previously: 7 PDF Tools | 5 Image Tools