// GUIDES
Understand the numbers
Plain-language explanations of the metrics our tools measure — what they mean, what counts as good, and how to fix them.
- What is TTFB (Time to First Byte)?TTFB measures how long your server takes to start responding to a request. Here's what it includes, what counts as a good TTFB, and why it matters.
- How to fix a slow TTFBA slow Time to First Byte is a server-side problem. These are the fixes that actually move it: caching, CDNs, database work, and hosting.
- What is a good Core Web Vitals score?Core Web Vitals are Google's three user-experience metrics: LCP, CLS, and INP. Here are the thresholds that count as good, and what each metric actually measures.
- How to check DNS propagationAfter changing a DNS record, resolvers around the world update at different times. Here's how propagation works, how long it takes, and how to check it.
- Why is my website down?A site can be down for everyone or just for you. Here's how to tell the difference, the most common causes, and what to check in what order.
- SSL certificate expired: what happens and how to fix itWhen an SSL certificate expires, browsers block the site with a full-page warning. Here's why certificates expire, how to fix it, and how to prevent it.
- What is website latency? (and what counts as good)Latency is the round-trip time between a visitor and a server — distinct from bandwidth. Here's what adds to it, typical values, and how to reduce it.