free tools for developers and SREs.
Small, fast calculators and generators, no sign-up. We built them for our own work watching uptime and kept them free for yours.
Uptime SLA & Downtime Calculator
Turn an uptime percentage into allowed downtime per day, week, month and year. A free SLA and SLO calculator with the full nines reference table.
Cron Expression Generator & Parser
Build and read cron expressions in plain English, with the next run times and a reference table of the most common schedules. Free, no sign-up.
Error Budget & Burn Rate Calculator
Turn an SLO target and your measured availability into error budget spent, budget left and burn rate, with a burn-rate reference table. Free, no sign-up.
Incident Update Message Generator
Write clear investigating, identified, monitoring, resolved and maintenance messages for your status page. Free, private and generated in your browser.
DNS Lookup: Compare Two Resolvers Side by Side
Check A, MX, NS, TXT and CAA records against Cloudflare and Google at once and see where they disagree. Free, no sign-up, runs in your browser.
HTTP Header & Redirect Chain Checker
See every redirect hop, the final status code and the response headers a URL returns, the way an uptime monitor sees them. Free, no sign-up.
SSL Certificate Checker: Expiry and Chain
Read any public host's TLS certificate: days until expiry, who issued it, which names it covers and whether the chain is complete. Free, no sign-up.
Domain Expiry Checker: Date and Registrar
Check a domain's registration expiry date, days remaining and registrar using public RDAP data. Free, no sign-up. Set up monitoring before renewal is due.
Website Security Checker: SSL, HTTPS & Headers
Check your website's SSL certificate, HTTPS redirects and security headers. See observed issues and practical fixes in one free report. No sign-up.
Watch the things these tools measure.
Uptimepage checks your endpoints every minute, opens an incident the moment one fails, and shows the record on a public status page. Start free, no card.