Free tools
Calculators and testers we built for ourselves and decided to put online. No signup, no tracking beyond what the rest of the site already does, everything runs in your browser.
SLA Uptime Calculator
Convert an uptime percentage into allowed downtime per day, week, month, and year. Or go the other way: enter your downtime and get the percentage you actually hit.
CalculatorError Budget Calculator
Turn an SLO into a concrete error budget, see how much you've burned, and find out whether you'll make it to the end of the window at the current rate.
TesterCron Expression Tester
Paste a cron expression and get a plain-English description plus the next 10 run times, shown in your timezone and UTC side by side.
GeneratorOn-Call Rotation Generator
Enter your team, pick a handoff day and time, and get a full rotation schedule you can download as an .ics file for any calendar app.
TesterJSON Path Tester
Paste a JSON response, type a dot path like result.items[0].id, and see exactly what it extracts. Useful for writing API assertions.
Downtime Cost Calculator
Estimate what an outage costs you in lost revenue and engineering time, broken down per minute. Sobering numbers for your next infra budget discussion.
Why these exist
failover.io is uptime monitoring with alert chains that escalate from email to SMS to a phone call until someone acknowledges. These tools answer the questions our users kept asking around the product. Free plan covers 5 monitors at 60-second checks, no card required.
See how it works