# 10 Free Developer Utility Tools That Run Entirely in Your Browser

> Source: <https://dev.to/xueboyang1985/10-free-developer-utility-tools-that-run-entirely-in-your-browser-bd1>
> Published: 2026-05-31 00:10:28+00:00

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*