Guides
Short explanations of the numbers behind uptime, each with the maths worked out.
99.9 uptimeThree nines in every period and calendar month, what 99.9% SLAs promise and how it compares with 99.99%.Nines of availabilityThe full table, what each extra nine costs and why the month length matters.SLA, SLO and SLIIndicator, objective and agreement, and how an error budget follows from the SLO.Composite availabilityWhy a chain is weaker than its weakest link and what redundancy really buys.MTBF vs MTTRThe definitions, the four meanings of MTTR and the formula that links them to uptime.
Calculators and tools
Work out your own numbers with the calculators, or build and check a cron schedule.
Uptime calculatorAllowed downtime for any uptime or SLA percentage, or the percentage for any downtime.MTBF calculatorMTBF, MTTR, availability, failure rate, FIT and AFR from a failure log.SLO and error budget calculatorError budget in minutes and requests, burn rate and the alerts to set.Cron expression generatorA cron schedule in plain English, its next run times and lines for crontab, GitHub Actions and Kubernetes.Cron examplesCopy-ready schedules from every minute to once a year, and the ones cron cannot do.