Free Developer Tools
Calculate SLA downtime, estimate outage costs, and make the case for API monitoring.
Cron Expression Generator
Build cron schedules visually with presets, validate any expression, preview next execution times, and learn cron syntax.
SLA Uptime Calculator
What does 99.9% uptime actually mean? Calculate exact downtime in minutes, hours, and days per month and year for any SLA percentage.
API Downtime Cost Calculator
Estimate how much API outages cost your business per year. Input your revenue and dependencies to see the real impact.
Uptime & Downtime Calculator
Convert uptime percentage to exact downtime, calculate SLA costs, compare availability levels from 99% to 99.999%, and reverse-calculate required uptime from acceptable downtime.
Website Down Checker
Check if any website is down right now. Get instant HTTP status codes and response times for any URL.
CNAME Lookup
Look up CNAME, A, MX, NS, TXT, and other DNS records for any domain. Powered by Google's public DNS resolver.
HTTP Status Code Checker
Check any URL's HTTP status code, response headers, and redirect chain. Color-coded results for 2xx, 3xx, 4xx, and 5xx responses.
SPF Record Checker
Validate SPF records for any domain. Parse mechanisms, check the 10 DNS lookup limit, get a security grade, and learn how to fix common SPF issues.
DKIM Record Checker
Look up DKIM records for any domain. Auto-detect selectors, check key length and strength, and get security recommendations.
DMARC Record Checker
Parse DMARC policies, check alignment settings, verify reporting configuration, and get a security grade with actionable recommendations.
MX Record Lookup
Find MX records for any domain. See mail server hostnames, priorities, and automatically identify the email provider.
Reverse IP Lookup
Find the hostname behind any IP address. Check PTR records, identify hosting providers, and verify reverse DNS configuration.
Beyond Free Tools
Need 24/7 automated monitoring?
These tools are great for one-off checks. For continuous monitoring with instant alerts, uptime tracking, and beautiful status pages — we recommend Better Stack.