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.
Each tool is one HTML file. No React, no Vue, no build step. Vanilla JS + browser APIs:
Hosting: GitHub Pages (free, global CDN). No server-side code. No database. Format, validate, minify JSON. Convert between JSON and CSV with smart type inference. Handles nested objects and big integers.
Compare two texts side by side. Line-by-line and character-level diff using Longest Common Subsequence algorithm. Highlights insertions and deletions.
Encode/decode text and files to/from Base64. Also includes hex and binary modes. File drag-and-drop support.
Generate UUID v4 (random) and v7 (time-ordered). Batch up to 100 at once. Uses crypto.getRandomValues() for true randomness. crypto.getRandomValues() for secure randomness. Configurable length (8-128 chars), character sets, ambiguous character exclusion. Full entropy — no Math.random() shortcuts.
Generate QR codes for URLs, WiFi networks, email, SMS, and vCard contacts. Wraps qrcodejs library. Download as PNG.
Split-pane editor with live preview. GitHub-Flavored Markdown (tables, strikethrough, code blocks). Copy HTML or download.
Full URL and component encoding. Data URL generation. Handles edge cases like nested encoding and special characters.
Human-readable dates to Unix timestamps (seconds and milliseconds) and vice versa. Timezone-aware ISO 8601 support. Relative time display.
Binary, octal, decimal, hexadecimal. Fractional number support. Step-by-step conversion mode for learning.
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.
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 24 free browser tools — all client-side, no signup, no tracking.
Previously: 7 PDF Tools | 5 Image Tools