Exact Match

Also known as: EM

Exact match is the fraction of model outputs that match the reference answer character-for-character after normalization steps such as lowercasing and punctuation removal. It is the strictest automatic metric: a response that is correct in meaning but paraphrased the reference differently scores zero. Exact match is most appropriate for closed-form tasks such as short extractive QA, multiple-choice benchmarks, and structured data extraction where there is a single canonical correct form.