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HTTP Status CheckerStatus code, response time and server IP.SSL Certificate CheckerExpiry, issuer, TLS version and chain.DNS CheckerAll records plus propagation.Website Speed TestTTFB, DNS, TLS, download and compression.Outage Root-Cause FinderPinpoints whether DNS, TLS, the server or the content is failing.Security Headers CheckerHSTS, CSP and more, graded A to F.WHOIS LookupRegistrar, age, expiry, nameservers.What Is My IP AddressSee your public IP address, location network and reverse DNS.
1
Check
Run a free check on any website. We test from our servers, not your network.
2
Diagnose
Our tools pinpoint DNS, SSL, server, redirect and content problems and explain the fix.
3
Get alerted
Turn on free monitoring and get an email the minute something breaks.
Latest guides
All guides →Downtime & ErrorsCloudflare 520-526 Errors Explained: Meaning and Fixes for EachA code-by-code guide to Cloudflare 520, 521, 522, 523, 524, 525, 526 and 530 errors, with origin tests, SSL mode fixes and firewall rules that resolve them.10 min readSSL & SecuritySSL/TLS Certificate Errors Explained: Causes, Diagnosis and FixesDecode browser errors like ERR_CERT_COMMON_NAME_INVALID and ERR_CERT_AUTHORITY_INVALID, diagnose them with openssl and curl, and fix each root cause.10 min readDowntime & ErrorsWhy Is My Website Down? 12 Causes and How to Diagnose EachA layer-by-layer method for finding why your website is down, with 12 common causes, the commands that expose each one, and when to escalate to your host.10 min readDowntime & ErrorsERR_CONNECTION_REFUSED vs Timed Out vs Reset: What Each MeansUnderstand what ERR_CONNECTION_REFUSED, ERR_CONNECTION_TIMED_OUT and ERR_CONNECTION_RESET reveal about TCP, and how to diagnose each with nc, curl, ss and mtr.10 min readMonitoringA Blameless Incident Postmortem Template With a Worked ExampleWrite a blameless incident postmortem that drives real fixes: timeline, root cause vs contributing factors, 5 whys limits, a copy-paste template and an example.10 min readSSL & SecurityHow to Renew an SSL Certificate and Automate It for GoodLearn the certificate lifecycle, automate renewals with certbot, Caddy or acme.sh, add reload hooks, test with a dry run and monitor expiry before users notice.9 min read
Is it down?
HTTP Status CheckerStatus code, response time and server IP.Redirect CheckerTrace every 301/302 hop.Port CheckerIs a TCP port open? (80, 443, 22, 25...)Outage Root-Cause FinderPinpoints whether DNS, TLS, the server or the content is failing.Down From Where? (Multi-Location Check)Check reachability from each location we run probes in.Redirect DebuggerHop-by-hop redirect trace with loop and chain detection.Maintenance vs Outage DetectorTells maintenance pages, WAF blocks and parked domains from real outages.Cloudflare Error CheckerExplains Cloudflare 52x and 1xxx errors and who must fix them.
Health & Speed
Website Health CheckUptime, SSL, DNS, speed and security scored out of 100.Website Speed TestTTFB, DNS, TLS, download and compression.Core Web VitalsLCP, CLS, TBT and a Lighthouse score.Broken Link CheckerFind dead links and 404s on a page.robots.txt & Sitemap CheckerValidate robots.txt and sitemap.xml.Meta Tag & Social Preview CheckerTitle, description, Open Graph, canonical, viewport.Why Is My Website Slow?Enter your numbers, get ranked likely causes.Page Weight AnalyzerHow heavy a page is, by file type and first or third party.HTTP/2 & HTTP/3 CheckerHTTP/2, HTTP/3 advertisement and Brotli/gzip compression.Third-Party Script CheckerLists external trackers, ads, fonts and widgets a page loads.Client Site Health ReportOne printable report with uptime, SSL, speed, security and SEO basics.
Security & SSL
SSL Certificate CheckerExpiry, issuer, TLS version and chain.Security Headers CheckerHSTS, CSP and more, graded A to F.HSTS CheckerIs HTTPS enforced with Strict-Transport-Security?Blacklist (DNSBL) CheckerIs your IP or domain on a spam blacklist?Mixed Content CheckerFind insecure http:// resources on https pages.Cookie Security CheckerSecure, HttpOnly and SameSite flags.SSL Chain & Name DebuggerFinds missing intermediates, name mismatches and weak signatures.TLS Version CheckerWhich TLS versions a server accepts, with a grade.CORS Misconfiguration CheckerDetects reflected origins, null origin and credential misconfigurations.security.txt CheckerValidate security.txt against RFC 9116 and get a starter file.Bulk SSL Expiry CheckerCheck up to 50 domains at once and sort by expiry.Dangling DNS & Takeover CheckerFinds subdomains pointing at deleted cloud services.
DNS & Domain
DNS CheckerAll records plus propagation.MX LookupMail servers for a domain.Nameserver LookupWhich nameservers does a domain use?Email DNS Checker (SPF, DKIM, DMARC)SPF, DKIM and DMARC health.WHOIS LookupRegistrar, age, expiry, nameservers.Domain Age CheckerHow old is a domain?DNSSEC CheckerIs DNSSEC enabled and valid?Email Deliverability TestSPF, DKIM, DMARC, MX, reverse DNS and blacklists in one score.SPF & DMARC Record GeneratorBuild SPF and DMARC records and validate lookup limits.Subdomain FinderDiscover subdomains from certificate transparency logs.DNS HistorySee how a domain's DNS records changed over time.Domain Expiry WatchFree email alerts before a domain expires.SPF Record Checker & Lookup CounterValidates SPF and counts the 10-lookup limit.
Hosting & Network
What Is My IP AddressSee your public IP address, location network and reverse DNS.IP LookupIPs and reverse DNS for any domain.Reverse IP LookupOther domains hosted on the same IP.ASN LookupWhich network owns an IP?Hosting CheckerHost, ASN, CDN and server stack.CDN DetectorIs a site behind Cloudflare, CloudFront, Fastly...?HTTP Header ViewerEvery response header, after redirects.
Developer Tools
JSON FormatterPretty-print or minify JSON.JSON ValidatorCheck if JSON is valid.Base64 Encoder / DecoderEncode and decode Base64 (UTF-8 safe).URL Encoder / DecoderPercent-encode and decode URLs.URL ParserSplit a URL into protocol, host, path, params.JWT DecoderDecode a JSON Web Token.Keyword SuggestionsRelated searches and questions for any topic.Timestamp ConverterUnix time to date and back.Regex TesterTest JavaScript regular expressions.QR Code GeneratorURL or text to a downloadable SVG QR code.All Developer ToolsJSON, Base64, URL, JWT, timestamp, regex, QR in one place.
Monitoring & API
Uptime SLA CalculatorUptime % to allowed downtime, and back.Uptime Monitor24/7 checks with email and webhook alerts.Cron & Heartbeat MonitoringGet alerted when a scheduled job stops running.Uptime BadgesEmbed live uptime and status badges.Status PagesPublic status page for your site, API and services.HTTP Status Code GuideEvery common status code explained, with fixes.Developer APIRun every check from your own code.PricingFree, Pro and API plans.Incident Post-Mortem GeneratorTurn incident notes into a clean post-mortem write-up.Status Widget for Your WebsiteEmbed a live status card on any website.
Fix an error message
All error fixes →ERR_SSL_PROTOCOL_ERRORDNS_PROBE_FINISHED_NXDOMAINYour connection is not privateERR_TOO_MANY_REDIRECTSERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)Error 1020 Access denied. What happened? This website is using a security service to protect itself from online attacks.Access to fetch at 'https://api.example.com/data' from origin 'https://app.example.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.PHP Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 20480 bytes)
Is it down? Popular sites
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Start monitoring freeAbout SiteDownCheck
SiteDownCheck is a set of free diagnostic tools and an uptime monitoring service for website owners, developers and IT teams. Every check runs from our own servers and is rate limited to protect the sites it tests. We never test private or internal addresses. Read more about us or how we handle privacy.