Guides
Plain-English guides on the calculations behind our tools: business days, fuel cost, color conversion and character limits.
chmod 755 vs 644: Which Permissions to Use and Why
Two numbers cover almost every file on a web server. Here is what each one grants, and why the third number people reach for is usually a mistake.
What to Put in a .gitignore File
Adding a rule to .gitignore does nothing for a file Git already tracks. Here is what belongs in the file, and how to fix it when the rule seems to be ignored.
auto-fit vs auto-fill in CSS Grid
These two keywords behave identically most of the time, which is why the difference is so confusing when it finally shows up.
Why YAML Turns NO Into false
A list of country codes that silently lost Norway is the most famous YAML bug. The cause is type inference, and it affects more than booleans.
Why Red and Green Status Colours Fail
Red for error and green for success is the most common accessibility failure in interface design, and picking better shades is not the fix.
How to Calculate Business Days Between Two Dates
Counting business days looks simple until weekends and holidays get involved. Here's the method spreadsheets use, done by hand.
How to Calculate Fuel Cost for a Road Trip
Three numbers — distance, efficiency and price — are all you need to estimate a trip's fuel cost before you leave.
RGB to HEX Conversion Explained
RGB and HEX aren't different colors — they're the same three numbers written in two different number bases.
Character Limits for Social Media and SEO, at a Glance
A reference for the character limits worth knowing before you hit publish — and what actually happens when you exceed them.