LeedyBox Guides
Practical explanations for common image, PDF, developer and text tasks, including file formats, resizing, compression, photo metadata, favicons, PDF page editing, OCR, QR codes, data conversion, regular expressions, cron schedules, Unix timestamps, hashes, passwords and character counting.
Image Guides
Read guide →JPG vs PNG vs WebP vs AVIF
Compare image formats by compression, transparency, and common use.
Read guide →Choosing the Right Image Format for the Web
Choose formats for photos, graphics, logos, transparency, and animation.
Read guide →Resizing Images: Pixels, Aspect Ratio and DPI
Pixel dimensions and file size, keeping the aspect ratio, downscaling quality, DPI and print size, and image sizes for high-density screens.
Read guide →Image Compression Settings Explained
What JPG and WebP quality numbers mean, how PNG colour reduction causes banding, and how a target file size is reached.
Read guide →Cropping, Rotating and Flipping Images
Crop to common aspect ratios without losing too much resolution, fix photos that appear sideways because of EXIF orientation, and flip images without reversing text by mistake.
Read guide →Taking a Passport or ID Photo at Home
Photo sizes and pixels, head size, visible ears, glasses, light, background, printing at actual size and file size limits for online forms.
Read guide →Photo Metadata and EXIF: What It Reveals and How to Remove It
What EXIF, XMP and IPTC metadata can reveal about a photo (location, device, dates), what to keep, and how to check and clean files before you share them.
Read guide →How to Extract Text From Images With OCR
How OCR works, choosing the language, image quality tips for photos and screenshots, and how to check the results.
Read guide →Favicon Sizes, Formats and HTML Tags
Which favicon files a website needs, from 16-pixel ICO and PNG files to the Apple touch icon and manifest icons, with the HTML tags and design tips.
Read guide →Creating QR Codes and Barcodes That Scan
Error correction, quiet zone, print size, contrast, barcode formats and check digits.
Read guide →PDF Guides
Read guide →How to Convert Images to PDF
Combine images into a PDF and manage page order and settings.
Read guide →Reducing PDF File Size: What Works and What It Costs
What takes up space in a PDF, what turning pages into images removes, and smaller scans and exports.
Read guide →Extracting Text From PDFs: Text Layers and OCR
Text layers, garbled characters and CMaps, when OCR runs, what affects its accuracy, and checking the result.
Read guide →How to Reorder, Rotate and Delete PDF Pages
Why pages end up out of order or sideways, how the PDF rotation setting works, and what to check after reordering, deleting or inserting pages.
Read guide →Adding a Watermark to a PDF
When to watermark a PDF, how to keep pages readable, tiled marks, printing tips and what a watermark cannot do.
Read guide →Adding Page Numbers to a PDF
Placement conventions, unnumbered covers, Roman numerals for front matter, Page X of Y and continuing another document's numbering.
Read guide →Developer Guides
Read guide →Converting Between JSON, CSV and YAML
What each format is good at and what can change during conversion.
Read guide →Regular Expression Basics
Character classes, quantifiers, groups, flags and backtracking.
Read guide →How to Read Cron Expressions
Unix, Spring, Quartz and AWS fields, special characters and time zones.
Read guide →Hash Functions Explained
Checksums, MD5 vs SHA-256, HMAC, and why hashing is not encryption.
Read guide →Base64, URL Encoding and JWT Explained
How Base64 and percent-encoding work, what a JWT contains, and why none of them hides data.
Read guide →Strong Passwords and UUIDs
Length, randomness, entropy, and the difference between UUID v4 and v7.
Read guide →Unix Timestamps Explained
What Unix time is, how to tell seconds from milliseconds, and how time zones, daylight saving and the 2038 limit affect conversions.
Read guide →Number validator guides
Read guide →Spanish DNI, NIE and NIF
How the control letter is calculated, NIE prefixes X, Y and Z, and company NIFs.
Read guide →Turkish Identity Number
The T.C. Kimlik No check digits, why the last digit is even, and what the number does not reveal.
Read guide →Russian INN and SNILS
Check digits of 10- and 12-digit ИНН and of the СНИЛС, with worked examples and the 2026 order.
Read guide →Brazilian CPF and CNPJ
Check digits of the CPF and CNPJ with worked examples, and what the alphanumeric CNPJ of July 2026 changes.
Read guide →IBAN Structure
Country formats from the SWIFT registry and the MOD 97 check digits, validated and calculated step by step.
Read guide →Italian Codice Fiscale
How the 16 characters are built, the control letter step by step, omocodia and the numeric code.
Read guide →Text Guides
Read guide →How Words and Characters Are Counted
Graphemes, code points, UTF-16 units, bytes and word segmentation.
Read guide →Case Styles and Naming Conventions Explained
camelCase, snake_case and kebab-case by language, acronyms, headings and case rules beyond English.
Read guide →How Text Comparison Works
How diff tools match lines, how to read unified diffs, and how to prepare texts for comparison.
Read guide →Lorem Ipsum and Placeholder Text
Where lorem ipsum comes from, when placeholder text misleads, and what to check before publishing.
Read guide →Writing Amounts in Words
Checks, invoices and contracts: cents as 56/100, British and American "and", billions, and the same amount in 14 languages.
Read guide →Full-Width and Half-Width Characters
Why ＡＢＣ and ABC differ, half-width katakana with ﾞ and ﾟ, and look-alikes such as 〜 and ～.
Read guide →Removing Accents and Making URL Slugs
Vietnamese đ and tone marks, Turkish ı and İ, German ae and ss, and slug rules for URLs.
Read guide →Korean Names in English Letters
Surname first, no sound changes, Kim or Gim, and how Korean passports spell names syllable by syllable.
Read guide →Transliterating Russian: ICAO and BGN/PCGN
The ICAO passport table and BGN/PCGN compared letter by letter, with names and GOST 7.79 explained.
Read guide →Simplified and Traditional Chinese
Why 发 becomes 發 or 髮, Taiwan and Hong Kong forms, regional words and what to check before publishing.
Read guide →Audio Transcription and Subtitles
How Whisper reads a recording, base or small, fewer mistakes, and SRT and VTT subtitle files compared.
Read guide →Date Guides
Read guide →Japanese Era Names and Western Years
The first day of each era from Meiji to Reiwa, why 1989 has two names, 元年 and dates before 1873.
Read guide →The Thai Buddhist Era and Western Years
B.E. = A.D. + 543, the old 1 April new year, the nine-month year 2483 and old documents.
Read guide →Korean, Chinese and Vietnamese Lunar Calendars
Why Seollal, the Chinese New Year and Tết can fall on different days, leap months and lunar birthdays.
Read guide →Calculator guides
Read guide →How to Calculate Percentages
The five percentage calculations, percentage change, discounts and the original price, and percentage points.
Read guide →How to Calculate VAT
Add VAT or take it out of a gross price, the VAT fraction, rounding on invoices and VAT rates in 16 countries.
Read guide →Loan Repayment Methods Compared
Equal payments, equal principal, interest-only and flat-rate loans compared, with the payment formula and APR.
Read guide →Compound Interest Explained
The compound interest formula, compounding frequency and APY, monthly contributions and the rule of 72.
Read guide →BMI Categories by Country
WHO and CDC classes, the lower NICE thresholds, and the standards of Korea, Japan, China, Indonesia and Thailand.
Read guide →BMR and Daily Calorie Needs
Mifflin-St Jeor, Harris-Benedict and FAO/WHO/UNU equations, activity levels, and Japan's and Korea's 2025 standards.
Read guide →How to Calculate Age Exactly
Exact age in years, months and days, 29 February birthdays and the legal age rules of Korea and Japan.
Read guide →Korean Age Explained
International age, year age and counting age, the 2023 change, 29 February birthdays and lunar birthdays.
Read guide →Use the Tools
Guides explain the concepts; the tools perform the file operation.
Frequently Asked Questions
Are the guides connected to LeedyBox tools?
Yes. Each guide is designed around a practical problem and links to the relevant LeedyBox tool where appropriate.
Are these guides only about converting files?
No. They also cover format selection, file size, transparency, photo metadata, favicons, PDF structure and page editing, OCR, QR codes, data formats, regular expressions, cron schedules, timestamps, hashes, passwords and text counting.