Matrix Multiplication Calculator

This tool multiplies two square matrices and shows how each entry of the product is built. It accepts two fixed sizes, 2x2 by 2x2 and 3x3 by 3x3, and you type each matrix one row at a time with commas or spaces between the numbers. The product comes back as rows, followed by the row-by-column sum that produced every entry. Other shapes, including rectangular and larger matrices, are out of scope, and values are rounded to ten decimal places before they are shown.