Guides
Short, practical explanations for the problems our tools solve — which image format to pick, why a PDF is so big, how passport photo rules differ by country, how to check a download is genuine. Each guide stands on its own and links to the free tool that does the job.
HEIC vs JPG
Why iPhones use HEIC, how it compares with JPG, and when to convert.
JPG vs PNG vs WebP
When to pick JPG, PNG or WebP for photos, screenshots and logos.
Reduce PDF file size
Why PDFs get so big and what actually shrinks them.
Merge and split PDFs
Combine, separate and order PDF pages for forms and applications.
Sign a PDF without printing
Sign contracts and forms digitally, and know what counts as valid.
Instagram image sizes
The right pixel sizes for posts, stories, reels and profile photos.
Passport photo sizes
Dimensions by country and the rules behind most rejections.
Remove EXIF data
What photos reveal about you and how to strip it before sharing.
How to calculate VAT
The two formulas, worked examples, and the classic percentage mistake.
Strong passwords, explained
Entropy, length versus complexity, and when to use a passphrase.
Verify a download's checksum
Check downloads on Windows, macOS and Linux, and know what a match proves.
How to calculate a tip
Mental-maths shortcuts, splitting bills, and tipping customs abroad.
Unix timestamps explained
Seconds versus milliseconds, time zones, conversion, and the 2038 problem.
ISO week numbers explained
The ISO 8601 rule for week 1, and why week 53 exists.
QR codes that scan
Size, contrast, error correction and logos for codes that scan first time.
MP3 to WAV or FLAC?
Which lossless format to convert to, and why neither restores quality.
Trim & adjust audio online
Cutting a clip, fixing its volume, and avoiding clipping distortion.
MP3 ID3 tags explained
Title, artist, album art and the difference between ID3v1 and v2.
UUID v4 vs v7
Random versus time-ordered UUIDs, and which one fits a database key.
How to read a cron expression
The five fields, the symbols, and the mistake that runs a job too often.
HEX vs RGB vs HSL
The same color, three formats, and when to reach for each one.
How BMI is calculated
The formula, the categories, and what it genuinely doesn't measure.
Gross vs net salary
What actually gets deducted between your offer and your paycheck.
How to calculate a discount
Fast mental math, and why stacked discounts don't just add up.
Favicon sizes explained
Which icon sizes browsers, phones and Windows actually request.