How to Calculate CAPTCHA API Success Rate: Three-Layer Metrics, Formulas, and Effective Cost

CAPTCHA API "success rate" is not a single number; this article breaks it into three layers—API return rate, target site acceptance rate, and end-to-end completion rate—with formulas, numerator/denominator definitions, judging differences across image, token, score-based, and full-page WAF CAPTCHAs, plus latency percentiles, effective cost-per-thousand examples, and a credible controlled test plan.