When running A/B tests, you track primary and secondary metrics to measure the impact of your changes. However, relying only on these outcome metrics can put your experiment at risk. This is where guardrail metrics become essential.

What Are Guardrail Metrics?

Guardrail metrics are extra measurements you monitor during experiments to catch and prevent unintended negative effects. Think of them as safety checks: they make sure that, while you aim to improve key metrics, you do not accidentally damage other critical aspects of your product or user experience.

• Guardrail metrics are not your main success criteria;
• They are crucial for protecting users, business goals, and the integrity of your experiment.

Example: You might test a new feature that increases user engagement. But if it also causes a spike in errors or slows down your website, the experiment could be too risky to launch—even if your primary metric looks positive. Guardrail metrics help you spot these issues early, so you can make smart decisions and prevent costly mistakes.