Reliability & Performance
Uptime
The percentage of time a service is available and working, the headline reliability number hosts advertise.
Uptime is the share of time your service is actually up and serving requests, expressed as a percentage. It's the number every host puts on its marketing, usually as an SLA promise like 99.9% or 99.99%. The figure sounds abstract until you translate it into downtime: 99.9% still allows nearly nine hours of outage a year, while 99.99% cuts that to under an hour.
The important distinction is between stated and observed uptime. A provider's SLA is a promise backed by credits, not a measurement of what actually happened. This site tracks both a provider's stated SLA and its observed real-world uptime where available, because the marketing figure and the lived experience don't always match.
Uptime is also something you shape through architecture, not a number you simply purchase. A single server has a hard ceiling on reliability, while redundancy across multiple servers and zones is how you push past what any one machine can promise. The host's SLA is the floor, your architecture sets the rest.
Go deeper
- What an Uptime SLA Actually GuaranteesHow to read "99.9% uptime," what providers actually owe you when they miss it, and why the number matters less than the fine print.