Type the unbalanced equation with reactants on the left and products on the right, then press Balance. The balanced equation appears with the smallest whole-number coefficients and an atom-count check for every element.
Each compound becomes a column and each element a row of a linear system, with reactants positive and products negative. The tool row-reduces that matrix over exact fractions and reads the null-space vector, then scales it to the smallest positive whole numbers, so the answer is mathematically proven rather than trial and error.
It says so and explains why, rather than returning wrong numbers. The usual causes are an element appearing on only one side, a typo in a formula, or a redox half-equation missing its ions and electrons.
Use plain formulas separated by plus signs with -> or = between the two sides, for example C3H8 + O2 -> CO2 + H2O. Brackets are fine, existing coefficients are ignored and recalculated, and state symbols like (s) or (aq) are stripped automatically.