Enterprise teams evaluating web agent infrastructure typically ask about uptime. 99.9% availability, maybe 99.99% for mission-critical workloads. But when we write SLAs for web agents operating across thousands of sites, we've seen something strange: systems maintaining 100% availability while delivering zero correct results. Every request completes successfully. Every HTTP response returns 200. The infrastructure is "up." But every extraction triggers detection and returns error pages instead of data.

Traditional uptime metrics can't capture what's actually broken.

What Reliability Actually Measures

Standard SaaS metrics assume infrastructure designed to support access. Availability percentages, response times, throughput. Web agents operate in environments designed to prevent it. When we build enterprise infrastructure with observability and governance requirements, reliability splits into three dimensions that uptime simply can't measure.

Correctness under structural variation. Websites change CSS selectors without notice. A/B tests show different layouts to different sessions. Regional variants serve different content based on location. When we build extraction logic across thousands of sites, the question becomes: did we extract the right information from the right elements, even though the markup changed overnight?

A traditional system fails when infrastructure goes down. Web agents fail when they successfully extract data from the wrong DOM element because a class name changed. The request completed. The response looked clean. The semantic meaning was wrong.

Sustained performance under detection pressure. Bot detection systems examine browser fingerprints, analyze mouse patterns, deploy ML models achieving 96.2% detection accuracy. When detection systems flag traffic, traditional thinking says "the system failed."

But when you're operating web agents at scale, detection becomes an expected operating condition. Reliability means adapting request patterns, rotating infrastructure, maintaining data flow even when individual sessions get blocked. The infrastructure stays "available" while continuously adjusting to adversarial pressure. Traditional metrics miss this entirely.

Verification of semantic correctness. A successful HTTP 200 response doesn't mean you got the right data. You might have received an error page that returned 200, content from the wrong region, or data from an A/B test variant. Data quality in web scraping requires verifying you extracted the intended information. At scale (hundreds of thousands of pages daily) even small drops in correctness compound into business consequences that availability percentages can't predict.

Why This Category Matters

The gap shows up when teams move from pilot to production. Pilots work reliably in controlled testing. Consistent results, clean data, everything looks production-ready. Then they deploy to the live web and discover their reliability framework never anticipated that detection would block half their traffic, or that CSS changes would break extraction mid-deployment, or that regional variants would serve completely different markup.

When we write enterprise contracts for web agent infrastructure, the primary reliability metrics are data accuracy and coverage thresholds. We specify what percentage of extractions must return semantically correct data and what coverage across target sites is required. These measure what actually matters: can the business depend on this data for decisions?

Teams evaluating web agent infrastructure need to ask different questions. How do you guarantee data correctness when sites change? How quickly do you adapt when detection patterns shift? The web actively resists automation. Teams that bring SaaS mental models to web agent infrastructure end up measuring the wrong thing and discovering the gap only after deployment, when availability metrics look fine but business outcomes don't materialize.