Basic usage is pretty self-explanatory. Paste in a recipe and replace quantities with expressions in curly braces. Like "3 eggs" becomes {3x} eggs and then at the end of the recipe include a line like Scaled by {x:1}. The things in curly braces are called cells and they get rendered as fields you can edit. Change any field and the rest adjust themselves.
It turns out this is kind of a free-form spreadsheet and constraint solver. You can include equations in cells and Reciplier tries to find an assignment of values to all the variables that satisfies all the equations. Like if you include {a}^2 + {b}^2 = {c}^2 = {a^2 + b^2 = c^2} in the recipe template, you have a nifty interface for finding Pythagorean triples. (Btw, "2x" is short for "2*x" but "x2" is just a variable, not "x*2".)
This was originally vibe-coded by Cantor Soule-Reeves and Daniel Reeves with Claude and then mostly Codebuff for a while and then a mix of a bunch of things. See Calca.io for an example of some prior art.