I Built 20+ Free Dev Tools That Run Entirely in Your Browser

Why I Built This

As a developer, I constantly need small utilities: format JSON, encode Base64, generate UUIDs, test regex patterns...

There are plenty of online tools out there, but they all have issues:

• Some require registration
• Some are buried in ads
• Some might upload your data to their servers
• Some are terrible on mobile

Especially when handling sensitive data - debugging production API responses, processing config files with API keys - I always worry about data leaks.

So I decided to build my own tool site to solve these pain points.

Core Features

1. Runs Entirely in Your Browser - Privacy First

This is the most important part. All tools execute in your browser. Your data never gets uploaded to any server.

When you use the JSON formatter to process API responses, or the Base64 encoder to handle sensitive strings, that data only exists in your browser's memory. Close the tab, it's gone.

Technically, all processing logic is pure frontend JavaScript with no backend API calls. Open your browser's DevTools and check the Network panel - you'll see no data requests except loading the page itself.

2. Free, No Registration Required

Just open and use. No account creation, no login, no email required.

I know how annoying it is (for me too) when a simple tool asks you to register.

3. Multi-Language Support

Currently supports 6 languages: English, Chinese, Spanish, French, German, Japanese.

Just add the language code to the URL: /en/json-formatter for English, /zh/json-formatter for Chinese.

4. Mobile Friendly

All tools are responsive and work perfectly on mobile devices.

Sometimes you need to quickly process data on the go - just pull out your phone.

What Tools Are Available

Currently 20+ tools across several categories:

AI Development Tools

• Token Counter - Count tokens for GPT-4, Claude, Llama, etc.
• Function Calling Definition - Generate JSON Schema for AI function calling
• Prompt Template - Manage and test AI prompt templates
• Base64 Image to Data URI - Convert images to Data URI for multimodal AI
• JSON to TypeScript - Generate TypeScript types from JSON
• Markdown to API Doc - Convert Markdown to API documentation

JSON & Data Processing

• JSON Formatter - Format and minify JSON
• JSON Validator - Validate JSON syntax
• JSON to CSV - Convert JSON to CSV
• CSV Viewer - View and preview CSV files
• JSON Schema Generator - Generate schema from JSON
• SQL Formatter - Format SQL statements

Encoding & Conversion

• Base64 Encoder/Decoder - Base64 encoding/decoding (supports Unicode)
• URL Encoder/Decoder - URL encoding/decoding
• Text Converter - Text encoding conversion, fix mojibake
• Regex Tester - Test regular expressions

Generators

• UUID Generator - Batch generate UUIDs
• QR Code Generator - Generate QR codes, download as SVG/PNG
• Hash Generator - Generate MD5, SHA1, SHA256, SHA512
• API Key Generator - Generate random API keys

Other Tools

• Color Converter - Convert color formats (HEX, RGB, HSL)
• Timestamp Converter - Unix timestamp conversion
• Image Compressor - Compress images
• Webhook Tester - Test webhooks
• cURL Converter - Convert cURL commands to code

Tech Stack

Quick overview of the implementation:

• Framework: Next.js 14 (React)
• Styling: Tailwind CSS
• Deployment: Vercel
• Core Libraries:
  • crypto-js - Hash calculation
  • uuid - UUID generation
  • react-qr-code - QR code generation
  • Everything else uses native JavaScript APIs

The code is straightforward - each tool is basically a page component, ranging from 50 to 150 lines of code.

Common Use Cases

Here are some scenarios where I use these tools regularly:

Debugging API Responses
Backend returns minified JSON in one line. Can't read the structure at all. Use JSON Formatter to format it - instantly clear.

Handling Base64 Data
Sometimes need to encode images or files to Base64 for API calls, or decode to see the content. Previously used tools didn't support Unicode - now I fixed that.

Generating Test Data
Writing unit tests or creating mock data, need a bunch of UUIDs. UUID Generator can create 1000 at once - just copy and paste.

Testing Regular Expressions
When writing regex, never sure if it'll match what I want. Regex Tester shows matches in real-time.

Counting Tokens
Before calling GPT or Claude API, want to estimate token consumption. Use Token Counter for a quick estimate.

Try It Out

🔗 https://free-online.dev

Feel free to try it out. If you have any issues or suggestions, reach out via the contact page on the site.

Final Thoughts

I built this project mainly to solve my own needs and practice some skills. If it helps other developers, that's even better.

If you find it useful, feel free to share it with friends or colleagues.

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Tags: #webdev #tools #privacy #opensource #javascript

Contact: [e-mail]