Guides and How-Tos
Practical, plain-English guides written by the ToolWorld Online team. Each one explains a task from first principles, walks through a real example and points to the free tools that help you finish the job in your browser.
How to Compress Images for the Web Without Ruining Them
Pick the right format, set quality, resize, convert iPhone HEIC photos and strip metadata to make web images small, sharp and private.
7 min read · Updated 2026-10-29
How to Create Strong Passwords That Actually Protect You
Learn what makes a password strong: entropy, length versus complexity, passphrases, password managers, two-factor authentication and how hashing works.
7 min read · Updated 2026-10-29
How Mortgage Amortization Works: Payments, Interest and Payoff
See how a fixed-rate mortgage payment is calculated, why early payments are mostly interest, and how down payment, PMI and extra payments change the total cost.
6 min read · Updated 2026-10-29
JSON Explained: How to Format, Validate and Convert It
A practical guide to JSON syntax, common errors, formatting versus minifying, converting CSV to JSON, generating TypeScript types and Base64 in APIs.
7 min read · Updated 2026-10-29
WCAG Color Contrast Explained: Ratios, Thresholds and a Worked Example
Learn how WCAG contrast ratios are calculated from relative luminance, what AA and AAA require, and how to check your own color pairs step by step.
7 min read · Updated 2026-10-29
How to Merge, Split and Compress PDFs Without Losing Quality
A practical guide to how PDFs are built, how merging and splitting work, why some files barely compress, and how to keep documents private.
7 min read · Updated 2026-10-29
BMI, BMR and TDEE Explained: Formulas, Limits and a Worked Example
Understand how BMI, BMR and TDEE are calculated, what the Mifflin-St Jeor equation and activity multipliers mean, and where these estimates fall short.
6 min read · Updated 2026-10-29
How to Write a Professional Invoice: Elements, Terms and a Worked Example
Learn what every professional invoice should include, how to number invoices, set Net 15 or Net 30 terms, handle tax and late fees, and total it correctly.
6 min read · Updated 2026-10-29