I've been building a collection of free browser-based tools across 4 sites. Every tool processes data entirely in your browser using JavaScript — nothing is ever uploaded to a server.
Why Browser-Only?
- Privacy — Your data never leaves your device
- Speed — No network latency, instant results
- Reliability — Works offline after first load
- Trust — Open source, verify the code yourself
The Tools
ToolBox Online — 18 Tools
General-purpose tools for developers and everyone:
- Code Tools: JSON Escape/Unescape, GraphQL Formatter, TOML Formatter, Lua Beautifier, HTML to JSX
- Converters: Text to CSV, Pantone to Hex, IP to Hex, Hex to IP, Base64 Encode/Decode, JSON to YAML
- Calculators: Playback Speed, Geometric Progression, Combination Sum
- Generators: Random IP, Palindrome, UUID
DevToolKit — 10 Tools
Developer-focused utilities with higher complexity:
- TOML ↔ YAML conversion, SVG to JSX, SQL to MongoDB
- Cron Expression Generator, ENV File Generator, Nginx Config Generator
- Chmod Calculator, HMAC Generator, JSON to Zod
CalcHub — 10 Calculators
Practical calculators for real-world problems:
- LLM API Cost Calculator (compare GPT-4, Claude, Gemini pricing)
- TikTok Shop Fee Calculator, Marketplace Fee Calculator
- Freelance Tax Calculator, Salary Inflation Calculator
- EV Charging Cost, 3D Printing Cost, Electricity Cost
ImageToolKit — 10 Tools
Image processing without uploads:
- Resize, Compress, Crop, Circle Crop
- PNG ↔ JPG, HEIC to JPG conversion
- Watermark, Image to Base64, Color Palette Extractor
Tech Stack
All 4 sites share the same architecture:
- Next.js 16 (App Router) + React 19
- TypeScript + Tailwind CSS 4
- Deployed on Vercel (free tier)
- SEO-optimized with JSON-LD structured data
What I Learned
- Long-tail keywords work — Tools targeting specific queries like "pantone to hex converter" rank faster than generic terms
- Client-side processing is a feature — Users genuinely care about privacy
- SEO for tool sites is different — FAQ sections, how-to-use guides, and structured data matter more than backlinks
Open Source
All 4 projects are open source:
Which tool would you use the most? What's missing from the collection? I'm actively adding new tools based on demand.
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