Free Tools for Developers — JSON, Regex, Hash, Favicon Pack, In Browser | ToolKoala
For Developers
"I'm a developer. These are the utilities I keep open in pinned tabs — favicons, JSON, regex, hashes, encoders. No CLI install, no signup, no telemetry. — Milo 🐨"
You don't need most of these every day. But the day you need a SHA-256 of a string, a regex tester that doesn't lag, or 17 favicon sizes from one SVG — you really need them. This page is the curated dev utility shelf. Everything runs locally in your browser; nothing phones home; no rate limits.
The 3 tools you'll use most
- JSON Formatter / Validator — Paste, pretty-print, validate, minify. Handles deeply nested structures and gives sane error messages for broken JSON. Use it for API debugging when you don't trust your terminal pipe.
- Regex Tester — Live highlighting, capture groups, match count. Test against ECMAScript-flavored regex (the same engine your JavaScript uses). Quick replace preview included.
- Favicon Generator — One source image → all required sizes (16, 32, 48, 64, 128, 256, 512, 180 for Apple Touch, plus manifest.json). One ZIP, drop it into your
public/folder, done.
A real workflow: shipping a new app's favicon set
Common scenario: design gives you one SVG logo. You need a complete favicon set for the web app, iOS install banner, Android manifest, and Apple Touch. Here's the 5-minute path:
- Source from SVG: open SVG to PNG, rasterize at 512×512 with transparent background. Save the master PNG.
- Generate the set: drop that master into Favicon Generator. Get the full pack (favicon.ico, .png variants, Apple Touch, manifest.json) as a single ZIP.
- Unzip into
public/: copy paste into your project; the manifest.json includes the standard link tags you can drop into<head>. - Verify cross-platform: test in Safari (Apple Touch Icon), Chrome on Android (manifest), and a bare-bones browser tab (.ico fallback).
Five minutes. No CLI. No npm install. No "free for 3 generations" SaaS gate.
Full developer toolkit (by use case)
🧪 Data inspection & transformation
- JSON Formatter — Pretty-print, minify, validate
- CSV ↔ JSON — Convert between formats, preserves types
- YAML ↔ JSON — Lossless conversion both ways
- Markdown ↔ HTML — Quick render or extract
- Text Diff — Side-by-side comparison with highlighting
🔐 Encoding & hashing
- Hash Generator — MD5, SHA-1, SHA-256, SHA-512 in browser
- URL Encoder / Decoder — percent-encoding for URLs and query strings
- Image to Base64 — data URLs for inlining images in CSS/HTML
- Timestamp Converter — Unix ↔ ISO 8601, multiple timezones
🎨 Asset preparation
- Favicon Generator — Full favicon pack from one source image
- SVG to PNG — Rasterize at any resolution with transparent BG
- Convert Image — HEIC, WebP, PNG, JPG interconversion
- Compress Image — Squeeze assets for app/web delivery
- QR Generator — URLs, WiFi, contact cards; SVG and PNG output
🧪 Quick utilities
- Regex Tester — ECMAScript flavor, live capture groups
- Color Converter — HEX ↔ RGB ↔ HSL ↔ named colors
- Color Picker (from image) — Pick exact hex from a screenshot
- Unit Converter — Bytes, time, distance, temperature
- Word / Char Counter — Useful for LLM token budgeting
- Case Converter — camelCase ↔ snake_case ↔ kebab-case
"Why a browser tool instead of a CLI?"
Honest answer: for one-off operations, you don't want to write a 10-line Python script, you want a 3-second answer. For SHA-256 of a token, a regex check, a quick favicon set — a browser tool with no install, no requirements.txt, no permissions dialog is faster than your terminal.
The other case: these tools work on machines where you can't install software — borrowed laptops, restricted corporate workstations, public coworking computers. They're useful exactly when your usual toolbox isn't there.
For everything else (batch operations, scripting, CI/CD), stay in the CLI. These complement your terminal, they don't replace it.
Frequently asked
Are these tools accurate? I can't have a buggy hash function.
The cryptographic functions (MD5, SHA family) use the browser's native SubtleCrypto API — the same implementation Chrome uses for HTTPS. Regex uses the V8 regex engine (same as Node.js). JSON parsing uses native JSON.parse. If your browser is correct, these are correct.
Does my source code or data leak anywhere?
No. The tools run in your browser tab. The processing happens locally on your CPU. You can verify in DevTools → Network: drop a file or paste text, watch the network panel — no outbound requests with your data.
Can I use these in a script or CI?
These tools are interactive (browser-based). For scripting and CI, use proper CLI tools — they're the right shape for that. The browser tools fit the "I need this answer right now, in this tab" use case.
Why isn't there a tool for X?
Tell me. [email protected]. The roadmap is heavily reader-driven; if you ask for a JWT decoder, a YAML linter, a UUID generator, or any other dev utility, it has a fast track. The constraint is "must run in browser" — anything that needs server compute (LLM inference, large compilation) doesn't fit.
Why no dark/light theme on output panels?
There is — top right corner toggle. Setting persists across visits. The site defaults to your system's prefers-color-scheme.
Pin this page. The dev shelf you'll actually use.
Or jump to Regex Tester → · JSON Formatter →
— Milo 🐨 · [email protected]