Free Online Developer Tools

143+ tools that run entirely in your browser. No data sent to any server.

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JSON Formatter & Validator

Format, validate, and beautify JSON data with syntax highlighting.

Base64 Encode/Decode

Encode text to Base64 or decode Base64 back to plain text.

URL Encode/Decode

Encode or decode URL components for safe transmission.

JWT Decoder

Decode and inspect JSON Web Token header and payload.

UUID Generator

Generate random UUID v4 identifiers instantly.

Hash Generator

Generate MD5, SHA-1, SHA-256, and SHA-512 hashes from text.

Regex Tester

Test regular expressions against sample text with match highlighting.

Unix Timestamp Converter

Convert Unix timestamps to human-readable dates and vice versa.

Color Converter

Convert colors between HEX, RGB, and HSL formats.

Lorem Ipsum Generator

Generate placeholder text in paragraphs, sentences, or words.

Password Generator

Generate secure random passwords with customizable length and characters.

Markdown Preview

Write Markdown and see a live rendered preview side by side.

HTML Entity Encode/Decode

Encode special characters to HTML entities or decode them back.

CSS Minifier

Minify CSS code by removing whitespace and comments.

JavaScript Minifier

Minify JavaScript code by removing whitespace and shortening syntax.

SQL Formatter

Format and beautify SQL queries for better readability.

Cron Expression Generator

Build cron expressions visually with a human-readable preview.

.gitignore Generator

Generate .gitignore files for popular languages and frameworks.

Diff Checker

Compare two texts and see the differences highlighted line by line.

JSON to CSV Converter

Convert JSON arrays to CSV format for spreadsheet use.

QR Code Generator

Generate QR codes from any text or URL instantly.

Slug Generator

Convert text to URL-friendly slugs for SEO-friendly URLs.

Word Counter

Count words, characters, sentences, paragraphs, and estimate reading time.

Text Case Converter

Convert text between camelCase, snake_case, kebab-case, PascalCase, and more.

JSON to TypeScript

Generate TypeScript interfaces from JSON data automatically.

Image to Base64

Convert images to Base64 data URI strings for embedding in code.

Tailwind CSS Colors

Browse and copy all Tailwind CSS color palette values.

Chmod Calculator

Calculate Unix file permissions in octal and symbolic notation.

YAML ↔ JSON Converter

Convert between YAML and JSON formats instantly.

CSV to JSON

Convert CSV data to JSON array format.

Number Base Converter

Convert numbers between binary, octal, decimal, and hexadecimal.

HTTP Status Codes

Searchable reference for all HTTP status codes with descriptions.

Regex Escape

Escape special regex characters in a string for literal matching.

HTML to Markdown

Convert HTML markup to clean Markdown syntax.

Markdown to HTML

Convert Markdown text to HTML output.

JS Object to JSON

Convert JavaScript object literals to valid JSON.

JSON Path Finder

Explore JSON structure and find paths to every value.

Word-Level Diff

Compare texts and highlight differences at the word level.

JSON Tree Viewer

Visualize JSON data as an interactive collapsible tree.

Meta Tag Generator

Generate HTML meta tags, Open Graph, and Twitter Card tags for SEO.

Open Graph Preview

Preview how your page looks when shared on Facebook, LinkedIn, and X.

SVG to CSS Background

Convert SVG code to a CSS background-image data URI.

Tailwind to CSS

Convert Tailwind CSS utility classes to plain CSS properties.

Favicon Generator

Generate favicon PNG files from text or emoji with custom colors.

JWT Generator

Generate JWT tokens with custom header and payload for testing.

User Agent Parser

Parse user agent strings to detect browser, OS, and device type.

Placeholder Image Generator

Generate custom placeholder images with specified dimensions and colors.

Bcrypt Hash Generator

Generate bcrypt-format password hashes with configurable rounds.

TOML to JSON

Convert TOML configuration files to JSON format.

IP Address Info

Show your current public IP address, location, ISP, and timezone.

Code to Image

Turn code snippets into beautiful shareable PNG images.

Epoch Countdown Timer

Live Unix epoch clock with countdown timer to any date.

Box Shadow Generator

Generate CSS box-shadow with visual preview and live controls.

CSS Gradient Generator

Create linear and radial CSS gradients with color picker and angle control.

Flexbox Generator

Visual flexbox layout builder with live preview and CSS output.

.env ↔ JSON Converter

Convert between .env files and JSON format.

Text to Binary

Convert text to binary representation and back.

ASCII Art Generator

Convert text into ASCII art using canvas rendering.

Docker Run to Compose

Convert docker run commands to docker-compose.yml format.

Nginx Config Generator

Generate Nginx reverse proxy configs with SSL, gzip, and caching.

SQL to MongoDB

Convert SQL queries to MongoDB shell commands.

DNS Lookup

Query DNS records (A, AAAA, MX, NS, TXT, CNAME) for any domain.

SSL Certificate Checker

Check SSL certificate validity, issuer, expiration, and protocol for any domain.

IP Subnet Calculator

Calculate network address, broadcast, host range, and subnet mask from CIDR notation.

Robots.txt Generator

Generate robots.txt files with custom user-agent rules and sitemap URL.

Color Palette Generator

Generate harmonious color palettes using color theory (analogous, complementary, triadic).

Border Radius Visualizer

Visualize and generate CSS border-radius with individual corner controls.

XML Formatter

Format and minify XML documents with proper indentation.

Pomodoro Timer

Focus timer with 25-minute work sessions and 5-minute breaks.

Typing Speed Test

Test your typing speed (WPM) and accuracy with random programming quotes.

Barcode Generator

Generate barcode images from text with download option.

CSP Header Builder

Build Content-Security-Policy headers with visual directive editor.

Markdown Table Generator

Build Markdown tables visually with alignment controls and instant output.

JSON Schema Validator

Validate JSON data against a JSON Schema with detailed error reporting.

cURL to Code

Convert cURL commands to JavaScript, Python, or PHP code.

Markdown TOC Generator

Generate a table of contents from Markdown headings automatically.

JWT Expiry Checker

Check if a JWT token is expired and show remaining time until expiration.

HTML Minifier

Minify HTML by removing comments, whitespace, and redundant attributes.

JavaScript Beautifier

Beautify and format minified JavaScript code with proper indentation.

JSON Diff

Compare two JSON documents structurally and see added, removed, and changed values.

JSON Query

Query JSON with dot paths, array indexes, and wildcards to extract values.

Remove Duplicate Lines

Remove duplicate lines, sort, and clean up text lists.

Text Reverse & Repeat

Reverse characters, words, or lines, repeat text, and count occurrences.

AES Encrypt/Decrypt

Encrypt and decrypt text with AES-256-GCM and a passphrase, in your browser.

HMAC Generator

Generate HMAC signatures (SHA-1/256/384/512) from a message and secret key.

Caesar Cipher / ROT13

Encode and decode text with a Caesar shift cipher, including ROT13.

Morse Code Translator

Translate text to Morse code and back, with automatic direction detection.

JWT Signature Verify

Verify a JWT HS256/384/512 signature against a secret, locally.

HTTP Header Analyzer

Paste HTTP response headers to see what each one does and which security headers are missing.

CORS Config Generator

Build and understand CORS response headers for your API.

MIME Type Lookup

Find the Content-Type for a file extension, or search MIME types.

Cron Next Run Times

Enter a cron expression and see the next scheduled run times in your timezone.

Image Resize & Compress

Resize and compress images in your browser without uploading them.

Image Format Converter

Convert images between PNG, JPEG, and WebP locally.

EXIF Data Remover

Strip EXIF metadata (GPS, camera, timestamps) from images in your browser.

SVG Minifier

Minify SVG markup by removing comments, whitespace, and prologs.

Aspect Ratio Calculator

Calculate aspect ratios and scale dimensions while keeping proportions.

PX to REM Converter

Convert between px and rem/em based on a root font size.

Data Size Converter

Convert between bytes, KB, MB, GB, and binary KiB/MiB units.

JSON to XML

Convert JSON data to XML markup.

XML to JSON

Convert XML documents to JSON format.

CSV Viewer

View CSV data as a sortable table with instant column sorting.

JSON Sort Keys

Sort JSON object keys alphabetically, recursively.

File to Base64

Convert any file to a Base64 data URI in your browser.

Unicode Character Lookup

Inspect Unicode code points, HTML entities, and JS escapes for any character or emoji.

Find & Replace

Find and replace text with optional regex and case-insensitive matching.

Sort & Number Lines

Sort, number, reverse, or shuffle lines of text.

Whitespace Cleaner

Trim trailing spaces, collapse blank lines, and convert tabs to spaces.

Text Statistics

Analyze word count, reading time, reading ease, grade level, and keyword density.

RSA Key Generator

Generate an RSA public/private keypair in PEM format, in your browser.

Password Strength Checker

Test password strength and estimate entropy locally.

Random Token Generator

Generate cryptographically secure random tokens in hex, alphanumeric, or Base64URL.

Base32 Encode/Decode

Encode and decode Base32 (RFC 4648), used for TOTP secrets.

UUID Inspector

Validate a UUID and detect its version, variant, and v1 timestamp.

URL Parser

Break a URL into protocol, host, path, query, and hash components.

Query String ↔ JSON

Convert between URL query strings and JSON objects.

User Agent Generator

Copy realistic User-Agent strings for common browsers and bots.

JSON Payload Validator

Validate a JSON payload and see size, key count, and nesting depth.

.htaccess Generator

Generate Apache .htaccess rules for HTTPS, www, gzip, caching, and security.

Crontab Describe

Translate a cron expression into plain English.

Color Contrast Checker

Check WCAG AA/AAA color contrast ratios for accessibility.

CSS clamp() Generator

Generate fluid responsive font sizes with CSS clamp().

Cubic Bezier Editor

Visually build CSS cubic-bezier easing curves.

CSS Grid Generator

Build CSS grid layouts visually with live preview.

Timezone Converter

Convert a time across major world timezones with DST support.

Color Blindness Simulator

Preview how a color looks under common color-vision deficiencies.

JSON to Go Struct

Generate Go structs with JSON tags from sample JSON.

JSON to Python

Generate Python dataclasses from sample JSON.

JSON to Rust Struct

Generate serde-annotated Rust structs from sample JSON.

JSON to JSON Schema

Infer a Draft-07 JSON Schema from a sample JSON document.

3-Way Diff

Compare two versions against a common base and spot merge conflicts.

SQL EXPLAIN Formatter

Format EXPLAIN plans as an indented tree and flag costly operations.

Avatar Generator

Generate initials avatars with deterministic colors from a name.

API Mock Data Generator

Generate realistic mock JSON data from field names for API testing.

Semver Calculator

Bump and compare semantic versions (major/minor/patch).

GraphQL Formatter

Format and indent GraphQL queries, mutations, and schemas.

.editorconfig Generator

Generate an .editorconfig file with your indentation and formatting rules.

Dockerfile Linter

Check a Dockerfile for best-practice issues like unpinned tags and root user.

JWK to PEM

Convert RSA and EC JSON Web Keys to PEM format in your browser.

Protobuf Decoder

Decode raw protobuf wire data without a .proto schema.

ASN.1 / DER Parser

Parse DER-encoded ASN.1 (certificates, keys) into a readable tree.

WebAuthn Tester

Check WebAuthn support and run a passkey registration ceremony.

Cron to AWS EventBridge

Convert a Unix cron expression to AWS EventBridge cron syntax.

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Developer tools that run in your browser

DevKit is a set of 143+ utilities for the small, repetitive jobs that fill a developer's day: formatting a minified JSON response, decoding a JWT to inspect its claims, generating UUIDs or a secure password, converting a timestamp, testing a regular expression, or diffing two blocks of text. Each tool does one thing and does it without a server round-trip.

Everything runs client-side. When you paste data into a formatter or a decoder, that data is processed by JavaScript in your own browser and never uploaded. That makes DevKit safe to use with sensitive material — API keys, access tokens, internal payloads — that you would not want to send to an unknown backend. It also means the tools keep working offline once the page has loaded.

Common questions

Is DevKit free?

Yes. Every tool is free to use with no signup, no account, and no usage limits.

Is my data sent anywhere?

No. All processing happens locally in your browser. Nothing you type or paste is transmitted to a server.

Do I need to install anything?

No. DevKit works directly in the browser. You can optionally install it as a PWA for one-click access and offline use.

Which tools are available?

Formatters, encoders and decoders, generators, converters, calculators, and testers across 11 categories. Use the search box above or press Ctrl+K to jump to any tool.