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A complete index of every page on this site so you can find what you need fast.
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Free Tools
- Tools overview (on home)
- QR Code Analyzer
- QR Code Generator
- QR Code Photo Restore
- 2D Fluid Simulator
- GIF Animator
- Japanese Phone Number Generator
- Japanese Address Generator
- QR Code EC Tester
- RAW Preview Extractor
- Manuscript Paper Sheet Counter
- Browser Info Viewer
- Email QR Code Generator
- WiFi QR Code Generator
- Japanese Name Generator
- ISBN Converter (10 / 13)
- Kana to Romaji Converter
- Contact QR Generator (vCard/MeCard)
- Kansuji Converter
- Sort Image Visualizer
- Email Address Generator
- Corporate Number Check Digit
- QR Code Print Size Calculator
- Aspect Ratio Calculator
- PixelPurge
- Manga Maker (YAML / JSON)
- Check Digit Calculator
- ULID Generator
- Base64 Encode / Decode
- JSON Formatter & Validator
- Metal Stress Simulator 2D
- UUID Generator (v1 / v4 / v7)
- Full-width / Half-width Converter
- DPI Calculator
- Barcode Photo Restore
- Reading Time
- Japanese Dummy Text Generator
- Newline Converter
- Network Segment Designer
- Circle and Line Logo Maker
- JSON Diff
- Barcode Generator
- Location (geo) QR Code Generator
- Video to GIF
- Relationship Diagram Video Maker
- Image EXIF Editor
- Lorem Ipsum Generator
- 3D Model Viewer
- Queue Simulator
- Markdown Preview
- Test Data Generator
- Color Code Converter
- Number Base Converter
- Contrast Ratio Checker
- URL Parser
- HEIC/HEIF Converter
- Images to PDF
- Movo Blocks (block-built image animation)
- Subtitle Timing Adjuster
- Slug Generator
- Image to Base64 (Data URL)
- Bulk QR Code Generator
- Circle and Line SVG Designer
- Unicode Code Point Inspector
- Japanese Era (Wareki) Converter
- Unicode Escape / Unescape
- Unix Time Converter
- HTTP Status Codes
- MeCard QR Code Generator
- Bar Chart Race Maker
- NATO Phonetic Alphabet Converter
- Password Generator
- Date Difference Calculator
- Regex Visual Builder
- Image Format Converter
- 3D Rig Animator
- Filter Syntax Checker
- YAML / JSON Converter
- Subnet Calculator
- Character Counter
- Consumption Tax Calculator
- Time Duration Calculator
- Face Blur
- Ranking Video Maker
- Characters to Words
- URL Encode / Decode
- Dummy Company Name Generator
- SMS QR Code Generator
- UTM QR Code Generator
- Invisible Character Checker
- Case Converter
- Random Date Generator
- QR Code Capacity Checker
- Work Hours Calculator
- Animated Line Graph Maker
- Roman Numeral Converter
- Base58 Encode / Decode
- JSON Relationship Map
- Cron Expression Parser
- Time Zone Converter
- Hash Generator (SHA)
- Percentage Calculator
- CSV ⇄ JSON Converter
- Phone Number QR Code Generator
- Data Size Unit Converter
- Dummy Article HTML Generator
- Strip Mixer
- SRI Hash Generator
- Unicode Normalization Comparer
- Mojibake Repair
- HMAC Calculator
- Character Encoding Dump
- Text Diff
- JWT Decoder
- Regex Tester
- Line Tools
- Calendar Event QR Code Generator
- Calendar Event QR Code Generator
- Placeholder Image Generator
- CSS Unit Converter
- Test Barcode Number Generator
- Punycode Converter
- JSONL / JSON Converter
- CSV to vCard (.vcf)
- ISO 8601 Duration Converter
- Fixed-width / CSV Converter
- QR Code Color Contrast Checker
- Cron Expression Builder
- CSV Encoding Converter
- Find the Source of a Hash
- HTML Escape / Unescape
- Line Sorter & Duplicate Remover
- MAC Address Generator and Formatter
- Basic Auth Header Generator
- IPv6 Address Expander and Compressor
- JSON Schema Generator
- JSON to TypeScript
- chmod Calculator
- NanoID Generator
- Documentation IP Generator
- Business Day Calculator
- CSV Column Cut & Reorder
- Character & Word Frequency
- Meta Tag and OGP Generator
- Excel Serial Number Converter
- Age Calculator
- JSON String Escape / Unescape
- Base32 Encode / Decode
- .env and JSON Converter
- CSV ⇄ Markdown Table
- Lorem Ipsum by Character Count
- Text Wrapper
- Ruby (Furigana) HTML Generator
- MIME Header Decoder
- SQL IN Clause Builder
- Email Header Analyzer
- SPF / DMARC Record Checker
- QR Code with Logo
- QR Code Batch Reader
- HTML Table to CSV
- CSV Duplicate Rows
- ICS File Generator
- robots.txt Generator
- Set-Cookie Analyzer
- Cache-Control Analyzer
- JSONPath Evaluator
- Product Master Test Data
- Snowflake ID Decoder
- UUID Inspector
- otpauth QR Code Generator
- CSP Header Builder
- CRC Calculator (32/16/8)
- Morse Code Translator
Study Posters
- Study Posters (index)
- How QR Codes Work
- How Barcodes Work
- IPv4 Addresses
- Introduction to HTML
- Introduction to CSS
- Introduction to JavaScript
- How a Web Page Is Rendered
- Attacks on Servers
- CVE (Vulnerability Info)
- OSS (Open Source Software)
- How Binary & Hex Work
- How Hash Functions Work
- Color Codes & RGB
- How to Make a Strong Password
- What Is Base64?
- What Is JSON?
- What Is a UUID?
- How URL Encoding Works
- Computer Time
- How Diff Works
- What Is a JWT?
- HTML Escaping and XSS
- Naming Conventions
- What Are Regular Expressions?
- CSV and JSON
- Character Codes and UTF-8
- What Is Placeholder Text?
Tech Blog
- Tech Blog (article index)
- How to Restore an Unreadable QR Code from a Photo
- What Is an API? (REST, Endpoints, Auth)
- QR Code Mask Patterns
- Choosing Japanese Dummy Text
- Why a QR Code Won't Scan
- What Is URL Encoding? Percent-Encoding Explained
- What Is Unix Time? Epoch Seconds, Time Zones, and Year 2038
- What Is a Hash Function? SHA-256, Use Cases, and Why It's Not Encryption
- How Diff Works
- What Is a JWT? Structure, Signatures, and Use Cases
- HTML Escaping and XSS
- Naming Conventions and Case Styles
- Binary and Hexadecimal Explained
- What Is Lorem Ipsum? Origin, How to Use It, and a Free Generator
- Regular Expressions for Beginners
- CSV vs JSON
- Text Processing Tips
- What Is a UUID? (v4, collisions)
- Color Codes Explained (HEX/RGB/HSL)
- Counting Characters and UTF-8
- Subnetting and CIDR Basics
- What Is JSON? (syntax, formatting)
- What Is Base64? (UTF-8, URL-safe)
- Understanding QR Code Specifications
- Understanding Barcode Specifications
- Understanding QR Code Error Correction
- Sorting Algorithms Visualized
- Core Web Vitals Practical Guide
- How Top Engineers Use Claude Code
- Claude Code Project Workflow
- Building Test Scenarios with Claude Code
- Team Collaboration with Claude Code
- Documentation Management with Claude Code
- Armin Ronacher's Claude Code Workflow
- Simon Willison's Claude Code Workflow
- Boris Cherny's Claude Code Workflow
- Mitchell Hashimoto's AI Agent Workflow
- Claude Code Subagents
- Claude Code Hooks
- What Is a Check Digit (EAN-13, ISBN, Luhn)
- Wareki and Gregorian Conversion
- What Is a Code Point (Unicode, UTF-8)
- Characters to Words Conversion
- What Is YAML (vs JSON, Basic Syntax)