Developer Tools
Hashing, UUID, JWT, Base64, regex tester, JSON/YAML formatters, cron parser, code minifiers, code screenshots, and more everyday developer utilities.
65 tools
Mermaid Diagram
Draw flowcharts, sequence diagrams, Gantt charts, class diagrams, and pie charts from text code. Embed-ready for GitHub README, Notion, Obsidian. Download SVG/PNG.
Age Calculator (Western/Korean)
Enter your birth date and see Western (international) age, Korean counting age, and yeonnai (year age) at once. Reflects Korea's June 2023 standardization to international age. Useful for paperwork, medical prescriptions, insurance, job applications, and confirming legal age for alcohol or tobacco.
Lunar ↔ Solar
Convert Korean lunar and solar dates in both directions. Range 1391–2050, leap month support, and ganji display. Useful for converting your parents' or grandparents' lunar birthdays to solar, ancestral rites date conversion, checking Lunar New Year and Chuseok dates, and entering data for fortune telling.
Caesar Cipher / ROT
Encrypt and decrypt text with Caesar cipher. ROT13/ROT47 presets and custom 1–25 rotation. Useful for CTF challenges, hiding spoilers on forums, introductory cryptography study, and fun message encoding.
HTTP Status Codes
Search the meaning of HTTP response codes 100–599. RFC standard codes plus common non-standard ones (418, 429, etc.). Useful for API debugging, error screen analysis, backend response design, interview prep, and web dev study.
CSS Gradient
Build linear/radial gradients visually by adding and adjusting color stops, then copy the CSS code. Live preview. Useful for website backgrounds, button designs, card UI headers, mobile app gradients, and marketing page backgrounds.
Base Converter
Convert between decimal, binary, octal, and hex instantly. Negatives and decimals supported, with auto-digit grouping. Useful for coding/CS study, color code (#RRGGBB) analysis, IP address conversion, bitwise op debugging, and assembly learning.
HTML Entity
Convert special characters like &, <, >, ", ' to HTML entities (&, <, >) and back. Numeric entities for Korean and emoji are also supported. Useful for safely displaying code samples on blogs, XSS prevention, writing HTML emails, and validating sitemaps and RSS feeds.
Password Strength
Score password strength by length, character types, and predictability. Detects common passwords, repeated patterns, and keyboard sequences. Useful for checking new account passwords, confirming corporate security policy compliance, and security awareness training.
Color Contrast (WCAG)
Calculate contrast ratio between text and background and check WCAG AA/AAA compliance. Useful for design accessibility audits, government and public sector sites (accessibility required), accommodating visually impaired users, and mobile readability checks.
Lotto Number Picker
Generate Korean Lotto 6/45 numbers using Web Crypto's secure RNG. Multiple games at once, with exclude option. Useful for weekly lotto picks, company year-end party games, and school or club random draws.
JSON Formatter
Pretty-print or minify JSON. Reports syntax errors and supports key sorting. Useful for API response debugging, config file review, log/monitoring data analysis, and external data source cleanup.
URL Encoder
Percent-encode Korean and special characters for URLs, or decode them. Supports encodeURIComponent and encodeURI modes. Useful for building API querystrings, analyzing search URLs, recovering broken Korean URLs, and web debugging.
Hash Generator
Calculate SHA-256, SHA-512, SHA-1, and MD5 hashes of text or files instantly. Use for integrity verification and checksums. Useful for verifying downloaded files, checking backup integrity, comparing API signatures, and security study.
UUID Generator
Generate multiple cryptographically secure UUID v4s at once. Supports hyphen and uppercase options. Useful for database primary keys, API identifiers, temporary tokens, tracking IDs, and avoiding filename collisions.
Unix Timestamp
Convert Unix timestamps (seconds or milliseconds) to human-readable dates and back. Supports ISO 8601, local, and UTC display. Useful for database log analysis, API debugging, checking cookie/JWT expiry, and timezone conversion work.
Image ↔ Base64
Encode an image as a Base64 data URL, or decode a data URL back to an image. Useful for inline-embedding images in CSS or email, inline SVG icons, including images in React components, and avoiding caching for tiny icons.
CSV ↔ JSON
Convert CSV data to JSON array and back. First row recognized as header; quoted and comma-containing values are properly handled. Useful for sending Excel data to APIs, processing report data, DB backup cleanup, and data migration.
YAML ↔ JSON
Freely convert between YAML and JSON. Useful for Kubernetes, GitHub Actions, OpenAPI, Docker Compose, and Ansible config files, and quick conversions between the two formats.
SQL Formatter
Pretty-print complex SQL queries. Supports 14 dialects including MySQL, Postgres, SQLite, MSSQL, BigQuery, and Snowflake. Useful for cleaning up code before review, analyzing ORM-generated queries, and recovering one-line queries from logs.
Cron Parser
Enter a cron expression to get a human-readable description and the next N execution times. Supports 5-field and 6-field (with seconds). Useful for writing Linux cron jobs, validating GitHub Actions schedules, AWS EventBridge, and Vercel Cron settings.
IPv4 / CIDR Calc
From CIDR notation (e.g., 192.168.0.0/24), calculate the network address, broadcast, subnet mask, and usable hosts. Useful for designing internal networks, splitting AWS VPC subnets, writing firewall rules, and networking exam prep.
JWT Decoder
Decode JWT header and payload. See expiry and issuer at a glance. No signature verification — use for debugging only. Useful for API auth debugging, expired token diagnosis, OAuth flow analysis, and SSO token inspection.
CSS Shadow
Build box-shadow visually with sliders and copy the code. Supports multiple shadow layers with live preview. Useful for card UIs, button emphasis, modal lift effects, and Material Design elevation.
JSON ↔ XML
Freely convert between JSON and XML. Attribute handling and indent options. Useful for legacy SOAP API debugging, RSS feed processing, analyzing Korean government public API responses, and Korean finance/insurance/telecom data work.
D-Day Calc
Calculate days between two dates, D-day until a specific date, or the date N days from today. Useful for counting down to exams, weddings, military discharge, anniversaries, project deadlines, dating days, birthdays. Korean lunar calendar not supported.
Unit Converter
Convert length (m, km, inch, ft), weight (g, kg, lb, oz), temperature (°C, °F, K), area (m², pyeong, acre), and volume (L, mL, gallon). Useful for converting US-unit movies and cooking recipes, comparing overseas online shopping sizes, air cargo weight, and listing height/weight while traveling.
Regex Tester
Enter a regex pattern and flags (gimsuy) to see live matches. Supports capture groups and replacement preview. Useful for data extraction, writing input validation rules, log analysis, previewing VS Code or IDE search patterns, and learning regex.
Color Converter
Convert between HEX, RGB, and HSL color codes. A free tool for designers and developers. Useful for organizing design system colors, writing CSS, transferring colors from Photoshop/Illustrator, and standardizing brand colors.
Base64 Convert
Convert between text and Base64. URL-safe option supported, with automatic Korean handling. Useful for analyzing API auth tokens, JWT payload decoding, email attachment debugging, and safe data transmission encoding.
Password Generator
Generate cryptographically secure random passwords. Choose length, uppercase, numbers, and special characters. Useful for signing up for new accounts, rotating corporate passwords, setting Wi-Fi router passwords, and generating temporary tokens.
URL Slug
Convert Korean, spaces, and special characters into SEO-friendly URL slugs. Includes optional Korean romanization. Useful for blog post URLs, WordPress/Tistory/Notion page addresses, static site paths, and product URL cleanup.
HTML Minifier
Remove whitespace, comments, and line breaks from HTML to reduce file size. Commonly used for faster production loading, Core Web Vitals improvements, and saving mobile data.
CSS Minifier
Strip whitespace, comments, and unnecessary semicolons from CSS to save bytes. Useful for production optimization, page speed, and reducing CDN costs.
JavaScript Minifier
Minify and mangle JavaScript with Terser, including identifier shortening and dead-code elimination. Useful for library publishing, npm packages, and static site optimization.
JSON Diff
Compare two JSONs object-by-object to show added, removed, and changed keys. Useful for tracking API changes, diffing config files, comparing GraphQL responses, and verifying schema migrations.
Text ↔ Binary
Convert text to bit-level binary and back. Supports both ASCII and UTF-8. Useful for CS study, debugging, cryptography practice, and CTF challenges.
Text ↔ Hex
Convert text to hexadecimal and back. Useful for debugging, encoding checks, network packet analysis, embedded firmware work, and hex dump inspection.
ANSI → HTML
Convert ANSI terminal escape sequences to HTML so you can display terminal colors on web pages, blogs, and docs. Useful for sharing CI/CD logs, replacing screenshots, and showing colored command output in tech posts.
Keycode Viewer
Press any key to see its event properties in real time: key, code, keyCode, and which. Useful for shortcut development, game controls, form key handling, and IME input debugging.
File → Base64
Encode any file (images, PDFs, videos) as Base64 data URLs, and decode data URLs back to files. Useful for inline attachments, embedding small files in code, and turning files into text for debugging.
Unicode Lookup
Look up the Unicode codepoint (U+XXXX) and name of a character, or build a character from a codepoint. Useful for emoji analysis, font compatibility debugging, Hanja code lookup, and special character input.
SVG Minifier
Strip comments, extra whitespace, and editor metadata (Inkscape, Illustrator) from SVG files to shrink size. Useful for web icon optimization, React icon components, and load speed.
Data Size Convert
Convert between bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes. Both SI (1000) and IEC (1024) supported. Useful for disk capacity comparisons, bandwidth calculations, file size estimates, and cloud cost projections.
MIME Types
Search by file extension or MIME type, both directions. Useful for HTTP response header configuration, file upload validation, security policy writing, email attachment handling, and web server config.
CSS Colors
All 148 CSS named colors with their HEX codes, searchable. Useful for color inspiration while writing CSS, rapid prototyping, and writing design guides.
HTTP Methods
Summary of HTTP method meanings, usage, and idempotency. Useful for RESTful API design, backend learning, interview prep, and API documentation.
.env Parser
Convert environment variable files to JSON objects, or convert JSON back to .env format. Useful for debugging environment settings, migrating variables across systems, and validating CI/CD environment variables.
Hangul Jamo Decompose
Decompose Hangul syllables into initial/medial/final jamo, or compose them back. Useful for Korean search and autocomplete, IME conversion, phonological analysis, and learning to code Korean text.
Seconds → Duration
Convert numeric seconds (7200) to readable formats (2:00:00 or 2 hours) and back. Useful for video/music durations, log analysis, API response handling, and workout records.
bcrypt Hash
Generate and verify bcrypt hashes with adjustable cost factor. Useful for auth system development, test dummy data, and database checks.
ROT 1-25
Display results for ROT1–25 all at once. Useful for Caesar cipher brute-force decoding in CTFs, quickly finding the right shift when unknown, and cipher learning.
Sensitive Data Mask
Auto-detect and asterisk-mask card numbers, Korean Resident Registration Numbers, phone numbers, and emails. Useful for pre-share log checks, screenshot prep, hiding personal info in blog posts and presentations, and pre-analysis anonymization.
Text Similarity
Calculate Levenshtein edit distance and percentage similarity between two strings. Useful for typo detection, similar-word lookup, search autocomplete, and data deduplication.
Font Preview
Live preview how text looks in any font. Useful for CSS font decisions, website design mockups, Korean font comparisons, and choosing fonts for business cards or posters.
Random String
Generate strings with cryptographically secure Web Crypto random. Useful for API keys, session tokens, temporary IDs and passwords, invitation codes, and UUID alternatives.
User-Agent Parser
Extract browser, OS, device, and version from User-Agent strings. Useful for web log analysis, compatibility debugging, analytics segmentation, and bot/crawler identification.
Password Compare
Evaluate two passwords side by side to see which is stronger. Useful for before/after comparison when changing passwords, showing family or colleagues why weak passwords are risky, and security education materials.
JS Beautify
Re-indent minified or compressed JavaScript for readability. Useful for analyzing external libraries, reading others' code, debugging, and educational code unpacking.
Code to Image
Paste source code, choose a language, and get a beautiful syntax-highlighted screenshot (Carbon-style) as PNG. For blog/SNS sharing, showing off code on Twitter, embedding in Notion or slides, and code review captures. 16+ languages.
HTML to Image
Enter HTML and CSS, then download the rendered result as a PNG. Useful for demo/portfolio previews, design mockups, email template checks, and widget design output. Powered by html2canvas.
SVG Blob
Generate random organic, curved SVG blobs. Use as website background decoration, hero-section accents, logo supplements, or illustration backgrounds. Control complexity, randomness, and color. Copy SVG code or download PNG.
Data URI Generator
Convert images, SVG, or text into Base64-encoded Data URIs. Inline in CSS background-image, embed images in HTML emails, build single-file demos with no external requests, or embed small favicons. Auto-detects MIME type.
File Hash Verify
Upload a file and paste the expected hash to auto-verify integrity. Useful for verifying downloaded files, checking OS ISO/executable tampering, and Git commit matching. Supports MD5, SHA-1, SHA-256, SHA-512. Browser-only processing.
File Split/Join
Split large files into smaller chunks (e.g. 10MB) or rejoin pieces. For email attachment limits, KakaoTalk transfer limits, cloud upload chunking. Splits auto-name `.part1`, `.part2`. Browser-only processing.