Browser tool
WebP Converter & Resizer
Convert JPG, PNG, HEIC, and HEIF images to one or more WebP sizes without uploading them.
Useful for: Preparing phone photos and transparent images for blogs, websites, and other web projects.
Built by frontend engineer Wataru Ito
Wataru’s Web Lab
Useful browser tools, playful web experiments, and practical frontend notes. I build things that solve real tasks, then write about how they work, what failed, and what I learned along the way.
Featured Tools
Focused tools you can use directly in your browser.
Browser tool
Background Remover & Image Cutout
Remove image backgrounds and download a transparent PNG or WebP without uploading the source.
Useful for: Creating product cutouts, profile images, stickers, and transparent assets for websites.
Browser tool
Image Upscaler
Enlarge JPEG, PNG, and WebP images by 2× to 8× with Pica interpolation and light sharpening.
Useful for: Making small images larger without uploading them or generating imaginary detail with AI.
Browser tool
JSON, YAML, TOML & Query String Converter
Convert structured data between JSON, YAML, TOML, and nested Query Strings in either direction.
Useful for: Moving API payloads, configuration data, and search parameters between formats without uploading them.
Browser tool
Word Counter & Frequency Analyzer
Count words in real time, rank repeated terms, and highlight every exact occurrence in your draft.
Useful for: Reviewing repetition and word choice without uploading or saving the text.
Browser tool
Text to Image Generator
Turn multiline text into a polished square, portrait, or landscape image with local Canvas export.
Useful for: Creating social graphics for Twitter / X, Pinterest, Facebook, Instagram, and TikTok.
Browser tool
Emoji Copy & Paste
Search the complete Unicode Emoji 17.0 set by name, meaning, code point, or keyword.
Useful for: Adding the right emoji to merge requests, Slack, email, release notes, and documentation in seconds.
Browser tool
Micro Habit Development Sheet
Build a printable monthly tracker for small habits and repeatable daily actions.
Useful for: Planning a month of small actions and marking progress with checks, colors, or stickers.
Browser tool
Mandala Mind Map
A private, browser-based 9×9 canvas for goals, plans, and ideas.
Useful for: Expanding one central thought into eight themes and 64 practical actions or supporting ideas.
Games
Quick browser games with no signup required.
Number game
Arithmix
Hunt through a luminous number grid and solve rapid-fire arithmetic prompts before time runs out.
Good for: A fast, tactile number hunt spanning mental arithmetic and prime numbers.
Number game
Sort Break
Race through Bubble Sort or rearrange the numbers yourself. Definitely not interview prep.
Good for: A tiny sorting brain break with guided comparisons or free reordering.
Number game
Make 10
Trace neighboring numbers and combine them to hit the target before the 60-second timer runs out.
Good for: A quick arithmetic path puzzle with addition, subtraction, multiplication, and division.
Number game
Perfect Grid
Swap numbered tiles until every row, column, and diagonal reaches the same target sum.
Good for: A focused number puzzle with three grid sizes and no hints to give away the solution.
Word game
Daily Anagram
Unscramble ten familiar words and track completed numbered puzzles in your browser.
Good for: A quick word challenge with hundreds of selectable puzzle sets.
Word game
Anagram Solver
Enter 3–12 letters and find exact English anagrams, with common words shown first.
Good for: Checking a letter mix or exploring alternate arrangements.
Word game
Word Grid
Connect neighboring letters in a 4×4 grid and find as many familiar words as you can.
Good for: A relaxed word search with no timer and hundreds of selectable boards.
Word game
Sevenfold
Build a chain of words, follow the last letter, and loop through all seven letters back to the start.
Good for: A relaxed word chain with hundreds of selectable loops and no timer.
Creative
Creative coding, visual experiments, and interactive studies.
Coding study
AutoMata
A color-field study in which neighboring cells evolve together through flocking-like rules.
3D study variation
Kira Kira 3D
The color-flocking logic of AutoMata, expanded into a three-dimensional field of points.
Study variation
Angle Field
A field of small lines turns with its neighbors while the background drifts through color.
Things I’d Rather Not Forget
Build notes, technical lessons, travel, parenting, and other things worth keeping.
What Is the Best Primary Key?
5/11/2026Auto-increment IDs are fast and simple—but are they the best choice for a primary key? A practical breakdown of UUID v4, UUID v7, ULID, cuid2, Nano ID, and when each makes sense.
Is JavaScript pass-by-value or pass-by-reference?
3/25/2026A pragmatic explanation of how JavaScript handles values and references, with clear examples and mental models for understanding assignment and equality.
Micro Habit Development Sheet: Motivation for Grown-Ups
3/25/2026A simple, sticker-chart-inspired tool to help adults build habits, based on the same motivational trick that works for kids.
JavaScript Event Loop
3/24/2026Understanding how JavaScript handles asynchronous operations through the Event Loop, Macro Stack, and Micro Stack mechanisms.
Notes on Using Claude: Tips & Architecture
3/22/2026Key takeaways and best practices for using Claude and multi-agent architectures, including prompt design, skills, and error handling.
Other Notes
Occasional field notes from family travel and life between Japan and the United States.
In Japan? Get a Melon. A Whole One.
8/21/2026Tokyo has many luxuries, but few are as gloriously excessive—or as delicious—as a whole Sembikiya muskmelon.
Osaka with Kids: Castle Park & Kaiyukan Aquarium
3/23/2026Explore Osaka Castle Park and Kaiyukan Aquarium—two must-visit family destinations in Osaka. Includes tips for access, activities, and making the most of your visit with children.
Osaka with Kids: Universal Studios & More
3/20/2026A practical guide for families traveling to Osaka with children, featuring Universal Studios Japan, Kids Plaza, and Hug Museum. Tips for planning, access, and making the most of your visit.