Guides & How-tos
Practical guides on money, files, text, images and more — with the free tools to put them into action.
How to Make an Image Smaller Than 100KB (or Any Size) for Upload Forms
Photo too big for an upload form? Shrink any image under 100KB, 1MB or another limit in one step, see how forms count KB, and check ID photos first.
2026-10-18 ImageWhat Is HEIC? How to Convert iPhone Photos to JPG for Uploads
Why won't your iPhone photo upload? It is probably HEIC. Learn what HEIC is and how to convert it to JPG in your browser, on iPhone, Mac, or Windows, plus tips for sending photos of ID documents safely.
2026-10-17 ImageHow to Rotate and Flip Photos: Fix Sideways and Tilted Images
Photo showing up sideways or upside down? Learn why it happens and how to rotate, flip, and straighten images in your browser, on iPhone, Android, Windows, or Mac.
2026-10-17 CalculatorHow Many Weeks Are in a Month? Days, Weeks, Months and Years Conversion Chart
A month is about 4.35 weeks (4 weeks and 2–3 days). See the math, weeks per month and per year, 1,000 days in years and months, plus easy conversion charts.
2026-10-17 CalculatorDog & Cat Years to Human Years: Why ×7 Is Wrong (Charts by Size)
Convert dog and cat years to human years with the AKC dog age chart by size, the FelineVMA cat age chart and the UCSD DNA formula, and see why ×7 is wrong.
VideoHow to Add Chapters to YouTube Videos: Timestamp Rules and Fixes
Add chapters to your YouTube videos the right way: timestamp rules for your description (start at 0:00, at least three, 10+ seconds each), YouTube Studio steps, a fix-it checklist, and title tips.
VideoYouTube Thumbnail Size and Design: Specs, File Limits, and Mobile Tips
YouTube thumbnail specs after the 2025 update: 16:9, 3840×2160 recommended, up to 50MB from a computer or 2MB from the app, JPG/PNG/GIF. Plus how to set one and design tips for small screens.
VideoHow to Embed YouTube Videos on a Website or Blog: Options and Fixes
Embed YouTube videos on your site or blog: get the official iframe code, add it to WordPress, use start, end, autoplay, and loop options, make it responsive, and fix Error 153 and other playback issues.
VideoHow to Extract a Still Image from a Video: Screenshot vs. Frame Export
Get a full-quality still from any video: screenshot vs. frame export, finding a blur-free moment, PNG/JPEG/WebP, batch export, and copyright tips.
VideoHow to Convert a Video to GIF: Settings for Smaller, Sharper GIFs
Turn a video into a GIF: why GIFs are limited to 256 colors, settings that cut file size, recommended settings by use, and when MP4 or WebP works better.
FinanceWhat Is Compound Interest? Use the Rule of 72 to Estimate Doubling Time
Learn what compound interest is, how it differs from simple interest, and how to use the Rule of 72 to estimate how long money takes to double, with examples and long-term saving insights.
FinanceHow Much Do You Need for FIRE? The 4% Rule and Annual Spending × 25
Learn the basics of FIRE (financial independence, early retirement): the annual-spending × 25 formula and the 4% rule behind it, the four types (Fat/Lean/Coast/Barista), and key risks, with concrete examples.
FinanceHow to Choose a Mortgage: Variable vs. Fixed Rates, Repayment, Deduction
A clear guide to choosing a mortgage: variable vs. fixed rates, equal-payment vs. equal-principal methods, safe debt-to-income guidelines, prepayment, and the tax deduction.
FinanceJapan Retirement Lump Sum Tax Basics: Deduction & Net Guide
Understand how a Japanese retirement lump sum (taishokukin) is taxed: the service-based deduction, half-taxation, separate taxation, your net amount, and when to file a return.
FinanceCrypto Tax Basics in Japan: Miscellaneous Income and Filing Explained
A beginner-friendly guide to taxes on crypto profits in Japan: how miscellaneous income and progressive aggregate taxation work, when gains are realized, why calculation is hard, how it differs from stocks and FX, and when you must file.
CalculatorUnit Conversion Basics: Length, Weight, Temperature & Area Made Simple
A clear guide to converting length (m/inch/ft), weight (kg/lb/oz), temperature (Celsius/Fahrenheit), and area (m²/tsubo/tatami). Learn the key reference numbers, the Fahrenheit-Celsius formula, and where conversions come up daily.
CalculatorPercentage Basics: How to Find X% Of, What Percent, Change, and Discounts
Learn percentage math with formulas and examples: how to find X% of a number, what percent of the whole, rate of change, and discounts and tax, plus the most common mistakes.
CalculatorElectricity Cost & Savings: kWh, Unit Price, Appliance Wattage & Standby Power
A clear guide to calculating electricity costs (kWh × rate + basic charge): typical wattage by appliance like air conditioners and fridges, standby power, reviewing your contracted amperage and rate plan, and saving tips you can start today.
CalculatorCalorie and PFC Basics: Basal Metabolism, TDEE, and Target Ratios
A clear guide to basal metabolism and TDEE behind calorie counting, the roles and target ratios of PFC (protein, fat, carbohydrate), and how plans differ for fat loss and muscle gain. Not medical advice.
CalculatorDate & Day Calculations: Elapsed Days, Business Days, Days From Now
A clear guide to counting days between two dates, business days (excluding holidays), a date N days before or after, and weeks. Learn leap-year and endpoint cautions, plus uses for deadline management and anniversaries.
Updated 2026-10-17 DeveloperWhat Is JSON? A Beginner Guide to Syntax, Writing, and Common Errors
Learn what JSON is from the ground up: objects and arrays, the data types you can use, common syntax errors like trailing commas, and practical uses such as formatting, validation, YAML conversion, and diffing.
TextHow Mojibake Works and How to Fix It: Character Encodings, UTF-8 vs Shift_JIS
Understand why garbled text (mojibake) happens, from the ground up. Learn how character encodings (UTF-8, Shift_JIS, EUC-JP) work, why CSV files break in Excel, common email and web cases, and how to repair and convert text.
FinanceHow Much Do You Need to Live Off Dividends? Yield Math and Taxes
Learn how to plan the money needed to live off dividends: back-calculating the required investment from target dividend ÷ yield, the 20.315% tax and NISA tax-free benefit, dividend-cut risk, and a realistic high-yield strategy with examples.
FinanceGross vs. Net Salary in Japan: What Gets Deducted and How Much
Understand the difference between gross annual income and take-home pay in Japan: income tax, resident tax, and social insurance deductions, the 75–85% net-pay rule, a quick reference table, and the basics of deductions.
CalculatorHow to Calculate Japan Consumption Tax: Inclusive vs. Exclusive & Rounding
Learn how to calculate Japan consumption tax with formulas and examples: converting pre-tax and tax-included prices, the 10% and reduced 8% rates, inclusive vs. exclusive pricing, rounding under one yen, and invoices.
CalculatorDue Date Calculation and Counting Pregnancy Weeks (Naegele Rule)
A clear guide to calculating the due date with Naegele's rule and counting pregnancy weeks, months, and trimesters from the last period, plus why the due date is only an estimate. Not medical advice.
Calculator90-Minute Sleep Cycles: When to Sleep and Wake Up Refreshed
Sleep runs in roughly 90-minute cycles. Learn how REM and non-REM work, how to back-calculate bedtime and wake time, how much sleep you need, and habits to improve quality. Not medical advice.
DeveloperRegular Expressions for Beginners: Metacharacters and How to Write Regex
Learn how to write regular expressions from scratch: the core metacharacters . * + ? [] () | ^ $, quantifiers, common patterns for email, phone, and URLs, groups and replacement, and tips for learning regex.
DeveloperWhat Is Base64? How It Works, Its Uses, URL-Safe Encoding, and Size Growth
Learn what Base64 is from the basics: how it turns 3 bytes into 4 characters, its uses in data URIs, email attachments, and API tokens, URL-safe encoding, and why the data grows about 1.33x, plus key caveats.
DeveloperMarkdown for Beginners: How to Write Headings, Lists, Links, and Tables
A beginner guide to writing Markdown. Learn the core syntax for headings, lists, links, emphasis, code, and tables, plus how to export to HTML and PDF and use Markdown on GitHub and blogs.
DesignWeb Color Basics: HEX, RGB, HSL Conversion, Palettes, and Contrast
A beginner-friendly guide to web color: what HEX, RGB, and HSL mean and how they convert, opacity (alpha), WCAG contrast ratios for accessible color, and how to build a color palette.
ImagePhoto EXIF Data and Privacy: Check, Remove Location, Use Mosaic
Learn what EXIF data (timestamps and GPS location) embedded in photos is, the risks of social posting, how to check and remove location data, and how to hide details with mosaic to protect photo privacy.
Updated 2026-10-17 DeveloperWhat Is a Hash? MD5, SHA-1, and SHA-256 Differences and Uses Explained
Learn what a hash value is from the ground up: properties like one-way and fixed-length, the differences between MD5, SHA-1, and SHA-256, uses in tamper detection and password storage, salting, how it differs from encryption, and collision risks.
DeveloperWhat Is a Unix Timestamp? Epoch Seconds Since 1970 Explained Simply
Learn what a Unix timestamp (epoch time) is from the ground up: the meaning of seconds since 1970, its relationship to time zones, milliseconds, the Year 2038 problem, and converting to and from human dates.
FinanceNew NISA vs iDeCo: Differences, Which to Prioritize, and Using Both
Compare new NISA and iDeCo by tax exemption, withdrawal freedom, deductions, and limits. Learn which to prioritize and how to use both, explained by situation.
DeveloperWhat Is a UUID? v1 vs v4, How Uniqueness Works, and Collision Odds
Learn what a UUID is from the ground up: the 128-bit structure, the difference between v1 and v4, why values do not collide, collision probability, uses such as database primary keys, and how it differs from auto-increment serial IDs.
DeveloperHow to Write Cron: The 5 Fields, Symbols, and crontab Examples Explained
Learn how to write cron (crontab) from scratch: the meaning of the five fields (minute, hour, day, month, weekday), how to use * / , -, common examples like daily, hourly, and weekly, and pitfalls to watch for.
DeveloperWhat Is a JWT? JSON Web Token Structure, Signing, and Verification Explained
Learn what a JWT (JSON Web Token) is from the ground up: the header.payload.signature structure, Base64URL encoding, how signing and verification work, the exp expiration claim, and why you must never put secrets inside it.
ImageWhat Is WebP? Differences from JPEG/PNG, Benefits, and Caveats
A clear guide to the next-gen WebP image format: how it differs from JPEG/PNG/GIF, lossless vs lossy modes, browser support, the benefits for lighter files and faster pages, and conversion tips.
DeveloperWhat Is CSV? Delimiters, Quotes, and How to Avoid Garbled Text
Learn what CSV is from the ground up: comma delimiters, quoting, line breaks, why text gets garbled when you open files in Excel and how to avoid it, plus practical uses like viewing and JSON conversion.
UtilityTime Zone and Time Difference Basics: UTC, JST, and DST Explained
A clear guide to time zones and time differences: the difference between UTC and JST, how daylight saving time (DST) works, tips for scheduling meetings across countries, and how it all relates to Unix time.
CalculatorSale and Discount Math: X% Off, Stacked Discounts, and Effective Rate
Learn how to find the sale price for X% off, reverse the discount rate, the pitfall of stacked discounts, how tax and point rewards interact, and the effective discount rate, with examples.
UtilityHow to Focus with the Pomodoro Technique: Why 25+5 and How to Do It
Learn the Pomodoro Technique of repeating 25 minutes of focus plus a 5-minute break: the basics, why 25+5 works, how to run it, adding long breaks, and its benefits and caveats. Start today with a timer.
DeveloperData Size Units Explained: KB, MB, GB and Bytes vs bps
A clear guide to bits and Bytes, the KB–MB–GB–TB ladder, the 1000-vs-1024 difference (KiB, MiB), how bps connection speed relates, and typical file sizes—including why "1 TB shows as 931 GB."
ImageHow to Make a Favicon: Sizes, Formats, and HTML Explained
Learn how to make a favicon from the basics: its role, the needed sizes (16, 32, 180, 192, 512), ICO/PNG/SVG formats, the HTML <link> tags, apple-touch-icon settings, and creation steps you can do in a browser.
DeveloperWhat Is an IP Address? Subnets and CIDR (/24) Made Simple
A beginner-friendly guide to IP addresses and subnets: the 32-bit structure of IPv4, private vs. global addresses, CIDR notation such as /24, subnet masks, and network and broadcast addresses.
CalculatorWhat Is a Standard Score (Hensachi)? The Formula and What 60 or 70 Means
Learn what the Japanese standard score (hensachi) is from the ground up: how it expresses your distance from the mean divided by the standard deviation around a base of 50, the formula, what a score of 60 or 70 means as a top percentile under a normal distribution, why it lets you compare different tests, and its limits.
DeveloperWhat Is OGP? Meta Tag Basics, og:image Size, and How Social Cards Work
A beginner-friendly guide to OGP (Open Graph Protocol) and meta tags: the roles of title and description, the meaning of og:title, og:image, og:type, and twitter:card, how social platforms build share cards, the recommended 1200x630 image size, and how to verify your settings.
DesignColor Contrast Ratio and Accessibility: WCAG Levels, Relative Luminance, and Readable Palettes
Learn color contrast and accessibility from the ground up: the WCAG thresholds (4.5:1, 3:1 for large text, 7:1 for AAA), how relative luminance works, why contrast matters, designing for color vision diversity, and how to build palettes everyone can read.
FinanceAnnual, Monthly, Hourly Pay Conversion: Methods, Work Hours, Gross vs. Net
Learn how to convert annual salary into monthly and hourly pay from the basics: the work-hour assumptions such as 160 hours a month, the difference between gross and net, how to handle bonus-inclusive salaries, and what to watch when comparing job offers.
UtilityHow Wi-Fi QR Codes Work: The WIFI Format, Encryption Types, and Auto-Connect
Learn why scanning a Wi-Fi QR code connects your phone instantly: how to read the WIFI:S:SSID;T:WPA;P:password;; standard format, the WPA/WEP/none encryption types, hidden SSIDs, the auto-connect flow, and security cautions when printing or sharing it.
FinanceFreelance Taxes and Tax Returns Explained: Income Tax, Resident Tax, Insurance, Pension, Blue Return
A beginner-friendly guide to taxes and tax returns for freelancers and sole proprietors: income tax, resident tax, national health insurance, national pension, and enterprise tax, the difference between blue and white returns, deductible expenses, the 650,000-yen blue return deduction, and an overview of consumption tax (invoice system).
FinanceJapanese Car Tax (Shubetsu-wari) Basics: Rates by Engine Size, Kei Cars, Monthly Proration
A beginner-friendly guide to Japan's annual car tax (shubetsu-wari): rough rates by engine displacement, how it differs from the kei (light) car tax, why the April 1 owner is charged, monthly proration, the green-car reduction and the 13-year surcharge, and how to pay.
CalculatorHow to Calculate Fuel Cost: Formula From Distance, Real-World MPG, and Saving Tips
Learn what fuel economy (km/L) means and how to calculate fuel usage and cost from your driving distance. We cover why real-world economy differs from the catalog figure, tips to cut fuel costs, and how to compare costs with hybrids and EVs.
DeveloperWhat Is Dummy Text (Lorem Ipsum)? Why Meaningless Text, Its Origin, and Uses
Learn what dummy text (Lorem Ipsum) is from the ground up: the meaningless Latin-like text used in place of real copy, why meaningless text is used on purpose, its surprisingly old origin, uses in mockups and typesetting checks, and how it differs from Japanese dummy text.
DeveloperHow to Write URL Slugs: SEO-Friendly Rules and Non-English URL Pitfalls
Learn what a URL slug is from the ground up: how it relates to SEO, the basic rules of lowercase letters, hyphen separators, and short meaningful words, the encoding problem with non-English URLs, symbols to avoid, and redirect cautions when changing a slug after publishing.
DeveloperIntro to Mermaid: Draw Diagrams from Text — Flowcharts, Sequence Diagrams, and Gantt
Learn what Mermaid is from the ground up: how text turns into diagrams, the basic syntax for flowcharts (graph TD), sequence diagrams, and Gantt charts, how to write nodes and arrows, how to use it in GitHub and Notion, and the benefits of managing diagrams as code.
DesignColor Theory Basics and How to Build a Palette: Wheel, Complements, 70:25:5
A friendly guide to color basics: reading the color wheel, schemes such as analogous, complementary, and triadic, the 70:25:5 ratio of base, main, and accent, how to align tone (lightness and saturation), and the difference between HEX, RGB, and HSL for practical web palettes.
CalculatorMean vs. Median vs. Mode: Choosing the Right Measure of Center
A clear guide to the difference between the mean, median, and mode. Learn why the arithmetic mean is vulnerable to outliers, when the median works best for skewed data like income or land prices, where the mode is useful, and how to pick a measure of center by the shape of the distribution.
CalculatorWhat Is Standard Deviation? Variance, Calculation, the Normal Distribution
Learn what standard deviation is from the ground up: its meaning as a measure of spread, its relationship to variance (the square root), the step-by-step calculation, what large vs small values mean, the 68-95-99.7 rule of the normal distribution, and how it links to standard scores.
CalculatorHow to Calculate Area: Triangle, Rectangle, Trapezoid, Circle Formulas & Units
A friendly guide to finding area by shape: triangle (base x height / 2), rectangle and square, parallelogram, trapezoid, circle (radius x radius x pi), and rhombus, with worked examples. Plus how units like square meters, tsubo, and tatami relate.
CalculatorWhat Are BMR and TDEE? Mifflin-St Jeor Formula and Activity Factors Explained
Learn the difference between basal metabolic rate (BMR) and total daily energy expenditure (TDEE), and how to calculate them: the Mifflin-St Jeor formula, activity factors from 1.2 to 1.9, targets for cutting and bulking, and individual variation as a caveat.
DeveloperUnderstanding URL Structure: Scheme, Host, Path, Query, and Fragment
Learn URL structure from the ground up: the role of the scheme (https), host, port, path, query string (?key=value&), and fragment (#), how percent-encoding works, and the difference between absolute and relative URLs, explained for beginners.
DeveloperCharacter Encoding and UTF-8 Basics: ASCII vs Shift_JIS and Mojibake
A beginner-friendly guide to character encoding: the difference between ASCII, Shift_JIS, and UTF-8, how UTF-8 uses a variable length (1 to 4 bytes), what a BOM is, why UTF-8 became the world standard, and why garbled text (mojibake) happens.
DeveloperScientific Notation (E Notation) and Significant Figures Basics
A beginner-friendly guide to scientific (E) notation and significant figures: how to read forms like 1.5e3, how to express very large and very small numbers, counting significant figures, rounding, E notation in Excel and programming, and overflow.
CalculatorRounding Basics: Round Half Up, Round Up, Round Down, and How to Choose
A beginner-friendly guide to rounding: the difference between round half up, round up, and round down, how banker's rounding (round half to even) works, rounding sales tax, Excel's ROUND, ROUNDUP, and ROUNDDOWN, which digit to round at, and practical usage.
DeveloperCSV vs TSV: Delimiters, Quoting, Encoding, and When to Use Each
A clear guide to the difference between CSV and TSV: comma vs tab delimiters, how quoting handles values containing commas or line breaks, character encoding pitfalls, tips for importing CSV into Excel, when TSV is handy, and how both compare to JSON.
TextJapanese Manuscript Paper and Character Count: 400-Cell Pages, Conversion, and Counting Rules
A clear guide to Japanese manuscript paper and character count: how 400-cell genko yoshi works, converting characters to pages, how to count spaces, line breaks, and punctuation, why counts differ in Word and submission rules, and practical targets.
DeveloperHow to Read Roman Numerals: Meaning of I V X L C D M and the Rules
Learn how to read Roman numerals from the basics: what the seven letters I, V, X, L, C, D, and M mean, the additive and subtractive rules (IV=4, IX=9), how to write large numbers, use on clocks and in years, tips for converting to Arabic numerals, and why you cannot write 4000 or more.
DeveloperWhat Is a Number Base? Binary, Octal, and Hex Basics Made Simple
Learn the basics of number bases (binary, octal, hex): why computers use binary, the 0b/0o/0x notation, how to convert to and from decimal, the relationship between bits and bytes, and why hex is used for things like color codes.
CalculatorHow to Count Business Days: Weekends, Holidays, and N Days Later
Learn what a business day is from the ground up: working days excluding weekends and holidays, how to correctly count N business days later or earlier, the difference from calendar days, how to handle holidays and year-end breaks, and practical counting for deadlines and payment dates.
DeveloperNaming Conventions and Case Styles: camelCase vs snake_case vs kebab-case
A beginner-friendly guide to programming naming conventions. Learn the differences between camelCase, snake_case, kebab-case, PascalCase, and CONSTANT_CASE, per-language conventions in JavaScript, Python, and CSS, how to choose for variables, functions, constants, and file names, and tips for readability.
DesignCSS Easing and cubic-bezier Explained: ease vs linear and the 4 Values
A beginner-friendly guide to CSS easing and cubic-bezier. Learn the difference between ease, linear, and ease-in-out, what the four values in cubic-bezier(x1,y1,x2,y2) mean as control points, how the curve relates to motion, how to specify it in transition and animation, and how to craft natural movement.
CalculatorRunning Pace Basics: Pace, Time, Distance, and Target Pace Conversion
Learn what running pace (min/km) means from the ground up: the relationship between pace, time, and distance, target times for 5K, 10K, half, and full marathon with per-kilometer conversions, and pace guidance for beginners, with formulas and charts.
FinanceAre Point Rewards Worth It? Effective Price and % Reward vs % Discount
From the meaning of a reward rate, to calculating the effective price including points, the difference between an X% reward and an X% discount, stacking points, the true value of one point, and tips for telling whether a deal is really worth it.
FinanceHow Effective Is Mortgage Prepayment? Term-Shortening vs. Payment-Reduction
Learn how much interest mortgage prepayment can save, from the basics: the difference between term-shortening and payment-reduction types, how interest is reduced, why earlier is more effective, balancing with cash reserves, the trade-off with loan insurance and tax deductions, and points to check first.
CalculatorSteps, Distance, and Calories: Stride Length, and How Far and How Many Calories 10,000 Steps Are
Learn how to turn steps into distance and calories from the basics: stride-length guidelines based on height, the formula to convert steps to distance, how to estimate calories burned from body weight and distance, and roughly how far and how many calories 10,000 steps are.
DesignCSS Grid for Beginners: display:grid, the fr Unit, gap, and Responsive Layouts
Learn CSS Grid from the ground up: how to create a grid with display:grid, grid-template-columns/rows and the fr unit, spacing with gap, placement with grid-template-areas, responsive layouts using repeat, minmax, and auto-fit, and when to use Flexbox instead.
DesignCSS Units Explained: px vs em vs rem vs % vs vw, and When to Use Each
A beginner-friendly guide to CSS units px, em, rem, %, and vw. Learn absolute vs relative units, the difference between em and rem (parent-based vs root-based), using rem for responsive design, vw/vh with clamp, and respecting the user font size for accessibility.
DesignWhat Is HSL? Hue, Saturation, Lightness vs RGB/HEX and Color Tips
Learn what HSL is from the ground up: the meaning of hue (H), saturation (S), and lightness (L), how it differs from RGB and HEX, why it is convenient for adjusting color schemes, how to build tones by changing lightness and saturation, and the hsl() notation in CSS.
DeveloperPassword Management Basics: Reuse Risks, Strong Passwords, Managers, and 2FA
Learn the basics of safe password management: why reusing passwords is dangerous, what makes a password strong (length and complexity), memorable passphrases, using a password manager, two-factor authentication, anti-phishing tips, and how to check for breaches.
DeveloperHow to Write Markdown Tables: Pipes, Hyphens, Alignment, and Line Breaks
Learn how to write Markdown tables from the basics: building header and separator rows with pipes (|) and hyphens (-), left/center/right alignment set by the colon (:) position, line breaks and pipe escaping inside cells, and how tables render on GitHub and in Notion, with examples.
CalculatorFraction Basics: Simplifying, Common Denominators, and the Four Operations
Learn fraction basics from scratch: how to simplify and find common denominators, addition and subtraction (common denominators), multiplication and division (reciprocals), converting mixed and improper fractions, fraction-decimal conversion, and tips for reducing answers to lowest terms.
CalculatorHow to Solve Quadratic Equations: Formula, Discriminant, Factoring & Completing the Square
Learn how to solve quadratic equations from the basics: the general form ax^2+bx+c=0, the quadratic formula, using the discriminant D=b^2-4ac to count real roots, solving by factoring, completing the square, and the link to the parabola graph.
DeveloperWhat Is a MIME Type? The Content-Type Header, type/subtype, and charset
Learn what a MIME type (content type) is from the ground up: the role of the Content-Type header, the type/subtype format such as text/html and image/png, the charset parameter for character encoding, browser behavior, the relationship with file extensions, and a list of common MIME types.
TextWhat Is Word Frequency Analysis? Spotting Text Patterns for SEO, Summaries, and Editing
Learn what word frequency analysis is in plain terms: the basics of counting, how top words reveal a text's character, uses for SEO, summaries, and editing, stop words, the unique difficulty of segmenting Japanese, and trends and caveats behind frequent words.
DesignCSS Flexbox for Beginners: Main vs Cross Axis, justify-content, align-items
Learn CSS Flexbox from the ground up: how display:flex works, the main and cross axes, flex-direction, justify-content, align-items, flex-wrap, the roles of flex-grow/shrink/basis, common layouts like centering and even spacing, and how it differs from Grid.
FinanceGift Tax Basics: The 1.1M Yen Exemption, Tax Rates, and Settlement Options
A beginner-friendly guide to gift tax in Japan: the annual 1.1 million yen exemption under calendar-year taxation, how the tax and the general vs. special rates work, the inheritance-time settlement system, education and housing fund exemptions, the link to inheritance tax, and when you must file.
FinanceHow to Calculate Overtime Pay: Hourly Rate, Premium Rates, and Fixed Overtime
Learn how overtime pay is calculated from the ground up: how to find the hourly rate (base wage divided by average monthly scheduled hours), the premium rates of 25% for overtime, 25% for late-night, and 35% for holiday work, how fixed (deemed) overtime works, the over-60-hours premium, and worked examples.
DesignMedia Query Basics: How to Write @media, Breakpoints, and Mobile-First
Learn media queries, the foundation of responsive design, from the ground up: how to write @media, the difference between min-width and max-width, how to choose breakpoints, the mobile-first approach, the viewport meta tag, and combining them with relative units and clamp.
FinanceThe Time Value of Money: Present Value, Future Value, and Discount Rate
Learn the time value of money from the ground up: why money today is worth more than the same amount later, future value with compounding, present value via discounting, and how to apply it to investing and saving. This article is general information, not investment advice.
TextWhat Is Typing Speed (WPM)? WPM vs CPM, Japanese Input, and Tips to Get Faster
Learn what WPM means as a typing speed metric: the difference between WPM (Words Per Minute) and CPM, how to measure Japanese input speed, the relationship with accuracy, average benchmarks from beginner to advanced, and tips to type faster with home position and touch typing.
CalculatorCelsius vs Fahrenheit vs Kelvin: Temperature Conversion Made Simple
Understand the temperature units Celsius (C), Fahrenheit (F), and Kelvin (K) from the ground up: how they differ, the Celsius-Fahrenheit conversion formulas, Kelvin and absolute zero, the freezing and boiling points of water, how to read overseas weather forecasts, and easy tricks to convert in your head.
DesignWhat Is SVG? How Vector Images Work, vs PNG, and Why They Scale
Learn what SVG is from the ground up: the difference between vector and raster images (PNG/JPG), why it does not degrade when scaled, the XML-based text format, why it suits icons and logos, file size and optimization, and how to use it on the web.
DeveloperWhat Is XML? Structure, How It Differs From HTML, Uses, and JSON Comparison
Learn what XML is from the ground up: a markup language that expresses hierarchy with tags, the structure of elements, attributes, and text, the well-formed rules, how it differs from HTML, uses such as configuration, data exchange, RSS, and SVG, and a comparison with JSON.
CalculatorStandard, Beauty, and Model Weight Explained: How to Calculate Them with BMI
Understand the difference between standard, beauty, and model weight and how to calculate them. Covers the standard weight formula from BMI 22 (height in m squared times 22), beauty weight (BMI 20) and model weight (around BMI 18) targets, how they differ from a healthy weight range, and a sensible approach to weight management.
FinanceHow Resident Tax Works: Income & Per-Capita Levy, Prior-Year Basis, Deductions
Learn how Japanese resident tax works from the basics: the income-based levy (about 10% of taxable income) and the per-capita levy, why it is charged the year after the income is earned, deductions, special vs. ordinary collection, and its link to furusato nozei.
CalculatorWhat Is an ISO Week Number? How to Count Weeks Under ISO 8601
A beginner-friendly guide to ISO 8601 week numbers: the rule that weeks start on Monday and the week containing the first Thursday is week 1, how to find the nth week, how it differs from "the nth week of the month," and how to use it in work calendars and project management.
DesignColor Mixing Basics: Additive (RGB) vs Subtractive (CMY) Explained
A beginner-friendly guide to color mixing: additive mixing where light (RGB) turns white when combined, subtractive mixing where paint (CMY) turns black, adding colors on the web, making intermediate colors, complementary colors, and where intuition and reality diverge.
RandomProbability Basics: Coins, Dice, Independent Trials, and the Law of Large Numbers
Learn probability basics with coins and dice: probability as favorable outcomes divided by total, independent trials, the 1/2 of a coin and 1/6 of a die, finding the odds of several trials by multiplying, the law of large numbers, and the gambler's fallacy.
DeveloperData Size Units Explained: KB, MB, GB and the 1000 vs 1024 Difference
Learn data size units from the ground up: the relationship between bits and bytes, the meaning of KB, MB, and GB, the difference between SI prefixes (1000) and binary prefixes like KiB and MiB (1024), why storage and OS figures differ, how it differs from bps speed, and rough size references.
TextHow Emoji Work: Unicode Code Points, Skin Tones, and ZWJ Sequences
Learn how emoji are built from the ground up: Unicode code points, surrogate pairs, skin-tone variation selectors, the ZWJ mechanism that joins multiple emoji into one, why they look different across devices, and how all of this affects character counting.
DeveloperWhat Is ASCII? 7 Bits for 128 Characters, Control vs. Printable, and A=65
Learn what ASCII is from the ground up: how 7 bits represent 128 characters, the difference between control and printable characters, the A=65 / a=97 / 0=48 mapping rules, extended ASCII, the relationship with Unicode and UTF-8, and how to convert between characters and numbers.
DeveloperCommon Regex Patterns: Email, Phone, URL, ZIP, Date Examples and Pitfalls
Practical regular expression patterns for everyday use, with examples for email, phone number, URL, postal code, date, and full-width/half-width text. Covers metacharacters, quantifiers, and groups, plus why you should not over-trust regex.
DesignWeb Color Names and Color Codes: CSS Named Colors, Hex, and Web-Safe Colors
A friendly guide to web color names and color codes: CSS named colors like red and tomato, how they map to hex codes, web-safe colors, the pros and cons of using color names, and how to find the closest color name.
FinanceInterest Rate Basics: Annual Rate, Simple vs Compound, APR, and the Rule of 72
A beginner-friendly guide to interest rate basics: how annual, monthly, and daily rates relate, the difference between simple and compound interest, APR vs nominal rate, the Rule of 72 for estimating doubling time, what interest means for deposits and loans, and fixed vs variable rates.
DeveloperConverting HTML to Markdown: Supported Elements, Pitfalls, and When to Edit by Hand
A clear guide to converting HTML to Markdown: why you convert it for CMS migration and republishing, which elements convert (headings, links, lists, tables, code, images), what breaks or cannot convert, and how to balance automatic conversion with manual editing.
DesignWhat Is a Type Scale? Sizing Text by Ratio, From Theory to Practice
Learn the basics of the type scale (modular scale): the idea of stepping font sizes by a consistent ratio, common ratios such as the golden ratio 1.618 and 1.25 or 1.333, designing heading and body hierarchy, implementing with rem, and improving readability and consistency.
CalculatorWhat Is Denomination Calculation? Counting Bills and Coins by Fewest Pieces
Learn what denomination calculation is from the ground up: how to work out how many of each bill and coin you need for cash payroll or currency exchange, the fewest-pieces idea, preparing change, and use in registers and accounting.
FinanceWhat Is Depreciation? Straight-Line vs Declining Balance, Useful Life, and Small-Asset Rules
A beginner-friendly guide to depreciation: spreading the cost of fixed assets over their useful life, the difference between straight-line and declining-balance methods, acquisition cost, useful life and residual value, the small-asset special rule, and how sole proprietors handle it on a tax return.
FinanceWhat Is the Break-Even Point? Fixed, Variable Costs and How to Find It
Learn the meaning of the break-even point and how to calculate it: how to split fixed and variable costs, contribution margin and margin ratio, the formula break-even sales = fixed costs / margin ratio, the break-even ratio, the effect of price cuts and cost reductions, and use in business planning.
CalculatorWhat Is GPA? Calculation, the 4.0 Scale, and Japan vs. Overseas
Learn what GPA is from the ground up: the meaning of Grade Point Average, how grades like A/B/C are converted to points and averaged by credit weight, the 4.0 scale, differences between Japan and overseas, how it is used for study abroad and job hunting, and how to raise it.
DesignIntro to CSS Animation: @keyframes, the animation Property, and vs. transition
A beginner-friendly guide to CSS animation basics: defining motion with @keyframes, the meaning of the animation property's duration, timing-function, delay, iteration-count, and direction, the difference from transition, how to build common effects like fade and slide, and performance tips.
FinanceHousehold Budgeting Basics: Take-Home Pay, Fixed vs Variable Costs, Ideal Spending Ratios, and Savings Rate
A beginner-friendly guide to household budgeting: grasp your take-home pay, separate fixed and variable costs, learn ideal spending ratios for housing and food, understand your savings rate and pay-yourself-first saving, cut fixed costs, and build habits that last.
DeveloperWhat Are HTML Entities? Escaping < > & and Special Characters
Learn what HTML entities (character references) are from the ground up: why you cannot write < > & directly, named vs numeric references, a list of common entities, handling quotes inside attribute values, and how they relate to mojibake and XSS.
DeveloperWhat Is a REST API? HTTP Methods, Endpoints, and Status Codes Explained
Learn the basics of REST APIs from scratch: what an API is, the REST approach, HTTP methods like GET/POST/PUT/DELETE, endpoints and resource design, status codes, JSON requests and responses, query parameters, and an overview of authentication.
DesignDark Mode Basics: Switch Colors with prefers-color-scheme and CSS Variables
Learn the basics of dark mode support: why it matters, how to use the prefers-color-scheme media query, switching colors with CSS variables, avoiding pure black while ensuring contrast, adjusting images and shadows, and how to roll out an implementation.
FinanceWhat Is the Invoice System? Qualified Invoices, Registration, and Tax Credits
A beginner-friendly guide to Japan's invoice system: what a qualified invoice is, how registered businesses work, the link to the purchase tax credit, the impact on taxable and tax-exempt businesses, required invoice items, and what freelancers and sole proprietors should know.
CalculatorCooking Measurement Basics: Tablespoons, Teaspoons, Cups, and Grams
A beginner-friendly guide to cooking measurement basics: tablespoon (15ml), teaspoon (5ml), cup (200ml), cc vs ml, why volume (ml) and weight (g) do not match, substitutes when you have no measuring spoon, and gram conversions for common seasonings.
DeveloperBitwise Operations Basics: AND, OR, XOR, NOT, Shifts, and Masks Explained
Learn the basics of bitwise operations from scratch: the AND, OR, XOR, and NOT logic operations, left and right shifts, how to set and clear individual bits, masks and flag management, the link to powers of two, and real uses like permissions, color, and optimization.
DesignWhat Is the Golden Ratio? 1:1.618 Meaning, Nature, Design Uses vs Silver Ratio
Learn what the golden ratio 1:1.618 is in plain terms: examples in nature and art, how to apply it to layout, whitespace, and font sizes, the difference from the silver ratio 1:1.414, and how to avoid over-relying on it. Written for design beginners.
CalculatorHow Much Water Do You Need a Day? Weight-Based Targets and Tips
Learn how to estimate your daily water needs from body weight. Covers the weight x 30-35 ml guideline, water from food, how exercise and heat change the amount, the risks of overdrinking, and tips for steady hydration. General health information.
CalculatorWhat Are Heart Rate Zones? Max HR, the Karvonen Method, and Fat-Burning
A beginner-friendly guide to heart rate zones: estimating max heart rate (220 minus age), the Karvonen method using resting heart rate, the fat-burning and aerobic zone ranges, how to gauge exercise intensity, and how to measure resting heart rate. This article is general information, not medical advice.
FinancePlanning Savings From a Goal: How Much to Save Monthly, With Compounding
Learn how to work backward from "how much by when" to the monthly amount you need to save: a simple division estimate, calculating with a return (compounding), how to set return assumptions, and tips for realistic goals. General information, not investment advice.
DesignHow to Make an SVG Blob: Organic Shapes, Backgrounds, and Optimization
A beginner-friendly guide to blobs, the organic shapes popular in web design: what a blob is, how it is used in backgrounds and decoration, how it is expressed as an SVG path, the idea behind random generation, file optimization, and how to avoid overusing it.
CalculatorInternational Shoe Size Differences Explained: JP, US, UK, EU Conversion
International shoe sizes use different scales in every country. Learn how JP (cm), US, UK, and EU sizes relate, how men's/women's/kids sizes differ, why brands vary, how to choose when buying abroad, and how to measure your foot length correctly.
DeveloperWhat Is Two's Complement? Representing Negatives, Invert-and-Add-One, and Ranges
Learn two's complement from the ground up: how computers represent negative numbers, the invert-the-bits-and-add-one method, the role of the sign bit, overflow, and the ranges representable in 8/16/32 bits.
DesignMake Shapes with CSS clip-path: polygon, circle, Clipping, and Animation
Learn how to clip elements and images into custom shapes with CSS clip-path: how to write polygon, circle, ellipse, and inset, how to set coordinates, triangles and diagonal cuts, hover animations, and browser support with fallbacks, all for beginners.
FinanceFinance Basics: Principal, Yield, Compounding, Risk, and Diversification
A beginner-friendly guide to the financial terms you should know before saving or investing: principal, yield, compounding, risk and return, diversification, index investing, dollar-cost averaging, and liquidity. This article is general information, not investment advice.
DeveloperNetwork Speed Basics: bps vs Byte/s, Mbps, Real Speed & Download Time
Learn network speed basics in plain terms: the difference between bps (bits per second) and Byte/s, how to read Mbps and Gbps, why real-world speed is slower than advertised, and how to estimate download time from a file size in GB.
DeveloperConverting Between JSON and XML: Structure Mapping, Lost Data, and When to Use Each
A clear guide to converting between JSON and XML: how objects, arrays, and attributes map to each other, information that is easily lost in conversion, when to use each format, and pitfalls around attributes, namespaces, and types.
TextWhat Is the Caesar Cipher? How Letter Shifting, ROT13, and Cracking Work
Learn what the Caesar cipher is from the ground up: how this classic cipher shifts letters by a fixed amount, how to encrypt and decrypt, the idea of ROT13 and the key (shift amount), why a brute-force attack breaks it easily, how it differs from modern encryption, and how to use it for learning and fun.
CalculatorPermutations vs Combinations: nPr and nCr Formulas, Factorials, and Examples
Learn the difference between permutations and combinations from the ground up: the order-sensitive nPr and order-free nCr formulas, what factorials mean, worked examples like lotteries and team splits, repetition cases, and the link to Pascal's triangle.
CalculatorWhat Is Body Fat Percentage? How to Measure It, Targets by Sex and Age
Learn what body fat percentage is from the ground up: how it differs from BMI, estimation methods such as bioelectrical impedance (Tanita-style) and the Navy circumference method, targets by sex and age, how home body composition scales work and their margins of error, and a healthy range.
CalculatorWhat Is 1RM (One-Rep Max)? Formulas, %1RM Chart, and Goal-Based Loading
Learn what 1RM (one-rep max) is from the ground up: estimation formulas such as Epley and Brzycki, a %1RM chart showing the relationship between reps and weight, goal-based loading for strength, hypertrophy, and endurance, and how to measure it safely.
DesignHow to Build a CSS Loader: Spinners, Dots, Bars, Pulses, and UX Tips
Learn how to build CSS loaders (spinners) from the ground up: making a circle with border and border-radius, spinning it with @keyframes, dot, bar, and pulse animations, respecting prefers-reduced-motion, and UX tips on when to show a loader.
DesignHow to Make Gradient Text: background-clip:text and Fallbacks
Learn how to create gradient text in CSS from the ground up: how background-clip:text and text-fill-color (color: transparent) work, how to set the angle and colors of linear-gradient, browser support and fallbacks, where to use it in headings, and readability tips.
DeveloperJSON vs XML vs YAML: Differences, Syntax, Types, and When to Use Each
A clear comparison of JSON, XML, and YAML: their syntax, readability, comment support, and handling of types, plus which fits config files, data exchange, and APIs, how to convert between them, and a simple guide to choosing one.
CalculatorWhat Is a Factorial (n!)? Why 0!=1, Permutations, and Explosive Growth
Learn what a factorial (n!) is from the ground up: the product from 1 to n, why 0!=1, how the value grows explosively, its relationship to permutations and combinations, uses in probability and counting, and the overflow pitfalls in calculators.
DeveloperWhat Are Escape Sequences? Meaning of \n, \t, \\, \" and Language Differences
Learn what escape sequences are from the ground up: how characters with special meaning like newline (\n), tab (\t), backslash (\\), and quote (\") work, differences between languages, escaping in JSON, and common bugs and fixes for beginners.
DeveloperWhat Is a Query String? The ?key=value Structure, Multiple Values, and Percent-Encoding
Learn what a query string (query parameters) is from the ground up: the ?key=value&... structure, how to express multiple values and arrays, percent-encoding, how it is used with GET, and design pitfalls such as order, duplication, and length.
CalculatorBMI vs Body Fat Percentage: The Difference, How to Calculate, and Why Both Matter
Learn the difference between BMI and body fat percentage from the basics. BMI comes from height and weight, while body fat percentage is the share of fat in your body. See why a muscular person can have a high BMI but low body fat, the typical ranges, the limits of each, and why you should look at both.
DeveloperConverting Markdown to HTML: Syntax Mapping, How It Works, Safe Output
Learn how to convert Markdown to HTML from the ground up: how syntax like headings, paragraphs, lists, links, images, code, and tables maps to HTML tags, how conversion works, uses in blogs and CMSs, and how sanitization keeps the HTML output safe.
DeveloperHTML Formatting and Indentation: Readable Code, Nesting, vs. Minify
Learn HTML formatting and indentation from the ground up: how to choose an indent width, make readable code, visualize nesting, why formatting matters, how it differs from minify and when to use each, attribute line-break rules, and where auto-formatters help.
CalculatorHow to Find Volume: Cube, Cylinder, Cone, Sphere Formulas and Units
Learn how to find volume from the basics: formulas for cubes, rectangular prisms, cylinders, cones, spheres, and triangular prisms, the "base area × height" idea, the relationship between cm³, m³, and liters, volume vs. capacity, and worked examples.
CalculatorWhat Is the Pythagorean Theorem? Meaning of a²+b²=c², Finding the Hypotenuse, and Famous Triples
Learn what the Pythagorean theorem is from the ground up: the relationship a²+b²=c² describes in a right triangle, how to find the hypotenuse, famous integer ratios like 3:4:5, real-world uses such as distance between two points, and the idea behind the proof.
DesignCSS Button Design Basics: Padding, Radius, Color, Hover, Shadow, A11y
Learn the basics of designing buttons with CSS: padding, border-radius, background color, hover and active states, shadows and gradients, tap-friendly size and contrast, and accessibility points such as focus indicators, all explained for beginners.
DesignWhat Are Shades and Tints? Adding Black or White and Building Them in HSL
Learn the difference between shades (a base color mixed with black), tints (mixed with white), and tones (mixed with gray). This beginner-friendly guide covers adjusting lightness and saturation, tips for building beautiful color steps, and how to implement them in HSL.
FinanceWhat Is ROI? The Formula, Worked Examples, Annualizing, and ROAS vs. Yield
Learn what ROI (Return On Investment) is from the ground up: the meaning of the formula profit ÷ investment × 100, worked examples, how to annualize it over a holding period, how it differs from ROAS and yield, and how to use it in investment decisions and its limits.
TextHow to Use Japanese Dummy Text: Differences from Lorem Ipsum and Typesetting Tips
Learn what Japanese dummy text is from the ground up: why placeholder text helps you check layouts, how it differs from English Lorem Ipsum, how to verify Japanese-specific character width and line spacing, where it is useful in design comps and typesetting, and what to watch out for.
CalculatorWhat Is Pi (π)? Its Meaning (Circumference ÷ Diameter), Why ~3.14, and How to Use It
Learn what pi (π) is from the ground up: that it equals circumference divided by diameter, its value of about 3.14, how it is used for circumference, circle area, and sphere volume, approximations and precision, its history, and tips for everyday calculation.
DeveloperMinify vs Beautify: The Difference, When to Use Each, Source Maps & Reversibility
Learn the difference between minifying and beautifying code: minify shrinks file size for production, beautify improves readability for development. Covers when to use each, source maps, reversibility, and where they fit in the build pipeline.
DeveloperHTML5 Semantic Tags Explained: header, nav, main, article, section, and SEO
A beginner-friendly guide to HTML5 semantic tags: the role of header, nav, main, article, section, aside, and footer, how they differ from div, their effect on SEO and accessibility (screen readers), and how to think about correct markup.
DesignCSS Transition Basics: Properties, Hover Animations, and Smooth Motion
Learn the basics of CSS transitions: the four parts (property, duration, timing-function, delay), how to change color and size on hover, the difference from animation, easing tips for natural motion, and performance pitfalls.
ImageHow QR Codes Work: Error Correction, WiFi & Contact (vCard) QR Guide
A practical guide to how QR codes work, choosing error-correction levels, creating URL, WiFi, and contact (vCard) QR codes, and tips for printing and scanning reliably.
CalculatorBMI and Ideal Body Weight Explained: Formula, Ranges, and Limits
A clear guide to the BMI formula and judgment ranges, ideal vs. beauty weight, the limits of BMI such as ignoring muscle, and how to use it for health management. Not medical advice.
CalculatorWareki to Seireki: Conversion Basics & Era Chart (Reiwa, Heisei, Showa)
How to convert between Japanese era years and the Western calendar, with mental-math tips and a Reiwa/Heisei/Showa chart. Learn what Western year Reiwa starts from, era-change cautions, document use, and age calculation.
DeveloperHow to Create Strong Passwords: Length, Passphrases, and Management
Learn how to build secure passwords from the ground up: why length beats complexity, the danger of reuse, memorable passphrases, the entropy metric, and using two-factor authentication and password managers.
TextHow to Count Characters: 400-Char Manuscript Pages, SNS Limits, Spaces & Line Breaks
Learn how to count characters correctly: converting to 400-character manuscript pages, character thinking for social media, reports and SEO, and how spaces, line breaks, and full-width vs half-width characters are counted.
ImageHow to Shrink Images Cleanly: Compression vs Resize vs WebP
Learn the three ways to lighten images (compression, resizing, format conversion), how they differ, lossless vs lossy, choosing PNG/JPEG/WebP, and tips for faster pages and email.
Updated 2026-10-17 DocumentsHow to Handle PDFs Safely: A Guide to No-Upload, In-Browser Tools
Learn the risks of uploading files to online PDF tools and why in-browser (client-side) tools are safer. Includes how to safely merge, split, compress, and convert images to PDF.
FinanceWhy Is Your Bonus Take-Home So Small? Japan Bonus Tax Explained
Learn why a Japanese bonus (shoyo) net amount is lower than gross: social insurance (health, pension, employment) and income tax withholding, plus a gross-to-net guide.
FinanceTaxes on Stock Profits: The 20.315% Rate and Account Types Explained
A beginner-friendly guide to taxes on stock and fund profits in Japan: the 20.315% rate breakdown, account types, loss offsetting and carryover, and tax-free NISA investing.
FinanceiDeCo Tax Benefits and Drawbacks Explained, With Limits by Occupation
A clear guide to iDeCo tax savings (full deduction, tax-free gains, payout deductions), drawbacks like no withdrawals until age 60, and contribution limits by occupation.
FinanceNew NISA Guide and the Power of Compounding｜30,000 Yen a Month for 20 Years
Learn the basics of Japan's new NISA (accumulation and growth frames, 18 million yen lifetime tax-free limit) and why compounding grows your money, with concrete examples and risk notes.
FinanceHow the Furusato Nozei Limit Is Decided: System, Income & Family Caps
A beginner-friendly guide to how the Furusato Nozei deduction limit is set—built around about 20% of your resident tax income levy—plus a 2026 table by income and family, who sees a lower limit after the 2026 tax reform, One-Stop vs. tax return, and key cautions.