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LocalDevToolbox

DEV

Your Data Stays Yours.

15 powerful developer tools — cURL converter, JSON formatter, JWT decoder, hash generator, regex tester, and more. All running locally in your browser. No server, no tracking, no data ever leaves your device.

Zero Tracking 100% Private Free Forever No Server
LocalDevToolbox — bash
$ curl -X POST https://api.example.com/v1/users \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer sk_live_...' \
  -d '{"name":"Ada","role":"admin"}'

# Convert to Python with one click
import requests

response = requests.request('POST', url,
  headers=headers, json=payload)
🔄

cURL Converter

Convert cURL commands to Python, JavaScript, Node.js, Go, PHP, Ruby, Rust, or C#. Or reverse: code back to cURL.

8 LANGUAGES
📋

JSON Formatter

Paste ugly JSON, get beautifully formatted, syntax-highlighted output with collapsible sections.

VALIDATE + FORMAT
🔐

JWT Decoder

Decode JSON Web Tokens. Inspect header, payload, and signature. Verify expiration and claims.

NO SERVER
🔤

Base64 Encode / Decode

Instantly encode or decode Base64 strings. Supports text, URLs, and binary-safe operations.

BIDIRECTIONAL
🔗

URL Encode / Decode

Encode special characters for safe URL transmission, or decode percent-encoded strings back to readable text.

QUERY FRIENDLY
🔍

Regex Tester

Test regular expressions in real-time. See matches, groups, and positions with live highlighting.

LIVE MATCHES
⏱️

Timestamp Converter

Convert Unix epoch timestamps to human-readable dates and vice versa. Supports milliseconds and seconds.

EPOCH ↔ DATE
#️⃣

Hash Generator

Generate SHA-256, SHA-512, and SHA-1 hashes from any text. Useful for verifying data integrity.

CRYPTO HASHES
📝

HTML Entity Encoder

Encode special characters to HTML entities (< → &lt;) or decode them back. Essential for web dev.

ENCODE + DECODE
📊

CSV ↔ JSON

Convert CSV data to JSON arrays or flatten JSON back to CSV. Handles headers and nested values.

BIDIRECTIONAL
🏷️

Type Generator

Generate TypeScript, Go, or Python type definitions from any JSON object or array. Paste API response, get types.

JSON → TYPES
🛠️

API Request Builder

Build cURL commands visually. Pick method, add headers, set body and auth — then convert to code instantly.

GUI → cURL
📑

Diff Checker

Compare two blocks of text side by side. Spot additions, deletions, and changes instantly. Perfect for API responses.

SIDE BY SIDE
🌐

URL Parser

Break down any URL into protocol, host, path, query params, hash. Rebuild or modify query strings with ease.

DECOMPOSE
🎲

Mock Data Generator

Generate realistic fake JSON data for API testing. Users, products, orders — customize count and fields instantly.

API TESTING

cURL Converter

cURL ↔ Code in 8 languages. Nothing leaves your browser.

$cURL command
Ctrl/Cmd + Enter
1
# Paste a cURL command on the left and hit Convert
Copied

JSON Formatter

Paste ugly JSON, get beautifully formatted output with syntax highlighting.

> Input (raw JSON)
Ctrl/Cmd + Enter
< Formatted output
Click ▸ to toggle nodes
# Paste JSON on the left and hit Format
Copied

JWT Decoder

Decode JSON Web Tokens. Inspect header, payload, and signature locally.

> Paste JWT token
Paste a JWT and hit Decode

Base64 Encode / Decode

Encode text to Base64 or decode Base64 back to text. All processing happens locally.

> Text to encode
Ctrl/Cmd + Enter
< Result
# Result appears here
Copied

URL Encode / Decode

Encode special characters for safe URL transmission, or decode percent-encoded strings.

> Text to encode
Ctrl/Cmd + Enter
< Result
# Result appears here
Copied

Regex Tester

Test regular expressions in real-time. See matches, groups, and positions.

/ Regular expression
> Test string
Matches update automatically
< Matches
Enter a pattern and test string to see matches.
Copied

Timestamp Converter

Convert between Unix epoch timestamps and human-readable dates.

> Unix timestamp
< Result
# Result appears here
Copied

Hash Generator

Generate cryptographic hashes from any text using SHA-256, SHA-512, or SHA-1.

> Input text
Ctrl/Cmd + Enter
< Hash output
# Hash appears here
Copied

HTML Entity Encoder

Encode special characters to HTML entities or decode them back to plain text.

> Text to encode
Ctrl/Cmd + Enter
< Result
# Result appears here
Copied

CSV ↔ JSON

Convert CSV data to JSON arrays or flatten JSON back to CSV format.

> CSV input
Ctrl/Cmd + Enter
< Result
# Result appears here
Copied

Type Generator

Generate TypeScript, Go, or Python type definitions from any JSON object or array.

> JSON input
Ctrl/Cmd + Enter
< Type definition
# Paste JSON and hit Generate
Copied

API Request Builder

Build cURL commands visually. Then convert to code with one click.

$ Request
< Generated cURL
# Fill the form and hit Build cURL
Copied

Diff Checker

Compare two blocks of text side by side. Spot additions, deletions, and changes instantly.

A Original text
B Modified text
Ctrl/Cmd + Enter
Δ Diff result
# Paste two texts and hit Compare
Copied

URL Parser

Break down any URL into components. Rebuild or modify query strings with ease.

> Paste URL

Mock Data Generator

Generate realistic fake JSON data for API testing. Customize count and schema instantly.

< Generated JSON
# Select a template and hit Generate
Copied

Developer Toolbox Guide

Complete reference for all 15 tools. What they do, when to use them, and how they work.

What is LocalDevToolbox?

LocalDevToolbox is a free, browser-based developer utility suite containing 15 powerful tools. Every operation runs entirely in your browser using JavaScript — no data ever leaves your device. There is no server, no tracking, and no cookies.

This guide explains what each tool does, common use cases, and the underlying algorithms. All tools are available instantly without registration.

🔄 cURL Converter

Parses cURL commands and converts them to Python (requests), JavaScript (fetch), Node.js (axios), Go, PHP, Ruby, Rust, or C# code. Also supports reverse conversion from code back to cURL. Uses a custom tokenizer to handle quoted strings, flags, headers, form data, and multipart uploads.

📋 JSON Formatter

Validates and pretty-prints JSON with syntax highlighting and collapsible tree view. Uses native JSON.parse() for validation. Supports minification and path-based node toggling.

🔐 JWT Decoder

Splits JSON Web Tokens into Header, Payload, and Signature components using Base64URL decoding. Displays claims like exp, iat, iss with expiration status. No signature verification (no secret key required).

🔤 Base64 Encode / Decode

Uses browser-native btoa() and atob() with UTF-8 safe encoding via encodeURIComponent. Handles text, URLs, and binary-safe operations in both directions.

🔗 URL Encode / Decode

Wraps encodeURIComponent() and decodeURIComponent(). Essential for preparing query strings, form data, and API parameters. Handles special characters, spaces, and Unicode.

🔍 Regex Tester

Compiles JavaScript RegExp objects with configurable flags (g, i, m, s). Shows all matches, capture groups, and positions in real-time. Useful for email validation, log parsing, and pattern extraction.

⏱️ Timestamp Converter

Converts between Unix epoch timestamps (seconds or milliseconds) and human-readable ISO/local dates. Uses native Date object. Includes "Use now" button for instant current timestamp.

#️⃣ Hash Generator

Generates SHA-256, SHA-512, and SHA-1 hashes using the Web Crypto API (crypto.subtle.digest). Useful for verifying file integrity, password hashing comparisons, and checksum generation.

📝 HTML Entity Encoder

Encodes special characters to HTML entities and decodes them back. Uses a temporary DOM textarea for accurate entity mapping. Essential for XSS prevention and HTML content generation.

📊 CSV ↔ JSON

Converts comma-separated values to JSON arrays and vice versa. Handles header rows, simple escaping, and basic nested structures. Useful for data migration, spreadsheet exports, and API payload preparation.

🏷️ Type Generator

Infers type definitions from JSON objects and generates TypeScript interfaces, Go structs, or Python classes. Recursively analyzes nested objects and arrays. Perfect for API integration when you only have sample responses.

🛠️ API Request Builder

Visual form for constructing cURL commands with method, URL, headers, body, and authentication. Outputs raw cURL that can be fed directly into the cURL Converter. Supports Basic Auth and Bearer tokens.

📑 Diff Checker

Compares two text blocks using a line-based LCS (Longest Common Subsequence) algorithm. Highlights additions, deletions, and inline character changes. Ideal for comparing API responses, config files, or code snippets.

🌐 URL Parser

Decomposes any URL into protocol, host, port, pathname, query parameters, and hash using the native URL constructor. Displays query params as a clean key-value list.

🎲 Mock Data Generator

Generates realistic fake JSON data for API testing. Includes templates for Users, Products, Orders, Blog Posts, Companies, and Employees. Supports custom field definitions. All data is generated locally using Math.random() — no external APIs called.

How to Use

1
Choose Your Tool

Pick from 15 available tools — cURL Converter, JSON Formatter, JWT Decoder, and more.

2
Paste Your Input

Enter your command, JSON, token, or text. No data leaves your browser.

3
Process or Convert

Click the action button and see the result instantly. All runs locally.

4
Copy or Download

Copy the output to clipboard or download directly for your projects.

Frequently Asked Questions

What is LocalDevToolbox?
A free browser-based developer utility suite with 15 tools. All processing runs locally in your browser — no data ever leaves your device.
Is my data private?
Yes. Zero outgoing requests. Verify with DevTools Network tab — you will see 0 requests when using any tool.
Do I need an account?
No registration, no login, no cookies. Open the site and use immediately.
Can I use it offline?
After initial load, yes. Save the HTML file locally and open it without internet.
What browsers work?
Chrome, Firefox, Safari, Edge. Web Crypto API requires HTTPS or localhost.
Is there a size limit?
No artificial limits. Very large inputs (MB+) may slow your browser since processing is in-memory.