Metrics for the Success of a New API

To track the success of a new external API, I focus on a tiered framework prioritizing developer velocity and reliability. First, I measure 'Time-to-First-Hello,' which tracks the minutes from account creation to a successful test call. At a company like Stripe, where frictionless onboarding is critical, reducing this time directly correlates to higher activation rates. Second, I monitor adoption depth using the ratio of unique API keys to total active endpoints called. A high number of keys calling only one endpoint suggests low stickiness, while diverse endpoint usage indicates deep integration. Third, reliability is paramount; I track 4xx versus 5xx error rates specifically during the first hour of integration to catch documentation gaps or genuine bugs immediately. Finally, I prioritize qualitative signals alongside quantitative ones. I would correlate support ticket volume regarding authentication errors with specific SDK versions to identify documentation issues. If we see a spike in 'timeout' errors for a specific region, it signals infrastructure needs rather than code problems. By balancing these technical performance indicators with developer satisfaction scores, we ensure the API scales sustainably without sacrificing the trust developers place in our platform.