An SLA (service level agreement) is a written commitment from a provider to a level of service, such as uptime, with compensation if it falls short.
An SLA, or service level agreement, is the part of a hosting contract that says what level of service the provider promises and what happens if it doesn't deliver. For web hosting, the headline figure is almost always uptime: a percentage such as 99.9% that tells you how much of the time your site should be reachable.
The important word is agreement. A host that calls itself fast and reliable is making a marketing claim. A host with an SLA is putting a number in writing, along with a remedy, usually a credit against your bill, if it misses that number.
What an SLA usually covers
A typical hosting SLA sets out:
- The uptime target, measured over a month or a year
- How downtime is measured and who measures it
- What counts as excluded downtime, such as scheduled maintenance
- The compensation you receive, often a share of your monthly fee as account credit
- How and when you need to claim it
What SLA uptime percentages mean
Small differences in percentages add up to big differences in real time. Over a 30-day month:
- 99% allows about 7 hours 12 minutes of downtime
- 99.9% allows about 43 minutes
- 99.99% allows about 4 minutes
So with a 99.9% SLA, if your site is down for more than about 43 minutes in a month, outside of excluded periods, the provider owes you the compensation the agreement sets out.
SLA exclusions to look for
Every SLA has exclusions, and they matter as much as the headline number. Common ones include scheduled maintenance, problems caused by your own code or plugins, attacks aimed at your site, and failures outside the host's network, such as a third-party DNS provider. AblePage's SLA, for example, gives account credit when uptime falls below 99.9%, and scheduled maintenance is excluded from SLA credits.
Why an SLA matters for your website
An SLA doesn't stop downtime from happening. What it does is show how confident a host is in its infrastructure, and it gives you a clear route to compensation if things go wrong. The credit is rarely worth much compared with lost sales, so treat the SLA as a signal of quality rather than as insurance.
How to check a host's SLA
Read the terms of service, not just the plan page. Look for:
- The exact uptime percentage and the period it's measured over
- How credits are calculated and whether they're capped
- The list of exclusions
- The deadline for making a claim
It also helps if the host publishes a status page, so you can see what's happening for yourself.