Each guide shows the manual approach first, then a short Apps Script version, then how Custom Count & Sum does the same thing in one formula that recalculates on its own.
Count or sum cells by color in Google Sheets
Three ways to count coloured cells — the built-in filter trick, a
custom function you paste yourself, and the add-on functions
COUNTBACKGROUNDCOLOR / SUMBACKGROUNDCOLOR.
Includes when each one breaks.
Count or sum bold, italic & strikethrough cells
Google Sheets can’t filter by font style at all. The manual
tag-and-filter workaround, an Apps Script function using
getFontWeights, and the add-on’s
COUNTSTYLE / SUMSTYLE / ISFONTSTYLE.
Sum or count across every sheet in a workbook
Google Sheets has no 3D reference. The hand-written sheet list, an
Apps Script loop over getSheets(), and the add-on’s
SUMALLSHEETS / COUNTALLSHEETS — plus the
tab-name gotcha that trips everyone up.
Count cells by conditional formatting colour
Why no formula, script or add-on can read a conditional-format colour, and the two approaches that do work: count by the rule’s own condition, or convert the highlight into a real fill.