Why Low False Positive Rates Matter as Much as Detection in Self-Hosted WAFs

Web Application Firewalls (WAFs) are commonly evaluated on attack detection rates, but false positive rate (FPR) — how often legitimate traffic is wrongly blocked — is equally critical for real-world deployments. A high FPR can disrupt customer logins, break partner API integrations, and cause alert fatigue that leads teams to weaken security rules over time. Traditional signature-based WAFs are prone to higher false positives because they match requests against fixed patterns, sometimes flagging unusual but valid inputs. Semantic detection engines, such as the one used by the self-hosted WAF SafeLine, aim to assess request intent rather than just pattern-match strings, which its published benchmarks suggest can reduce FPR to as low as 0.07%. Experts recommend evaluating any WAF against live traffic, reviewing detailed block logs, and treating vendor benchmarks as a starting point rather than a definitive measure.