Free, no account needed

Other Tools

Focused DNS utilities that answer one question well, with plain-language results and a clear next step.

Email & authentication

Email Validation

See how a domain receives mail and protects against impersonation. MX, SPF, DKIM and DMARC are checked together, each with what it does, where attention is needed, and how to fix common issues.

  • MXMail serversWhere the domain accepts email, in priority order.
  • SPFSender policyWhich servers may send mail for the domain.
  • DKIMSigning keysThe public key for a selector you name.
  • DMARCEnforcementWhat receivers do with mail that fails.

Email & authentication

Email Header Analyzer

Paste a message’s headers to see where it started, each server it passed through, and whether SPF, DKIM and DMARC passed for the From address. Diagrams show the route and how the envelope sender lines up with the header From. Parsed in your browser; nothing is uploaded.

Analyze headers

  • RouteHop pathEvery server from sender to mailbox, with delays and TLS.
  • EnvelopeEnvelope vs. FromThe bounce address SPF checks against the From the reader sees.
  • AuthSPF, DKIM, DMARCThe receiving server’s verdicts, in plain language.
  • AlignAlignmentWhether a passing check counts for the From domain.

Search & discovery

Search and AI Optimizer

See how search engines and AI assistants find a site. robots.txt, sitemaps, feeds and llms.txt are read together, a sample of listed pages is checked, and contradictory signals are explained with fixes. Crawler access is simulated from the site’s own files.

  • CrawlersAccess matrixSearch, AI search, training and on-request agents.
  • SitemapsSitemaps and feedsValidity, limits, freshness and broken links.
  • SignalsConflictsnoindex, canonical and robots.txt rules that disagree.
  • SubmitSubmission hubWhere to submit, and where only robots.txt applies.

Network & IP

TCP Port Check

Find out whether a port on a public host is open, closed or filtered. Three connections are timed from Cloudflare’s network, the handshake is drawn packet by packet, and services that speak first, such as SSH and mail servers, show their greeting.

  • StateOpen, closed or filteredWhether the host completed, refused or ignored the handshake.
  • HandshakeSYN, SYN-ACK, ACKA schematic of the handshake, inferred from the connection result. Packets are not captured.
  • TimingConnect timesThree attempts, with fastest, average and slowest.
  • BannerService greetingWhat SSH, SMTP, FTP and similar services announce.

Network & IP

Subnet Calculator

Work out an IPv4 or IPv6 subnet: network and broadcast address, usable host range, mask and wildcard. A bit-by-bit map shows which bits name the network and which number hosts, and a prefix slider lets you watch the block grow or shrink. Calculated in your browser.

  • BitsNetwork vs. host bitsEvery bit of the address, mask and network, colour-coded.
  • RangeAddress rangeNetwork, usable hosts and broadcast, with your address marked.
  • SplitSubnet splitterDivide a block into smaller subnets and list each one.
  • IPv6IPv4 and IPv6Masks, wildcards, special ranges and reverse DNS zones.

Network & IP

What Is My IP

See the address websites see when you visit them, over IPv4 and IPv6, with your provider’s network, an approximate location and the Cloudflare data center you reached. A diagram shows where NAT changes your address on the way out.

Show my IP

  • IPIPv4 and IPv6Both public addresses, and which one this page used.
  • ASNProviderThe network and routed address block you belong to.
  • GeoRough locationCity, region and time zone from IP data, with its limits.
  • PathConnection pathDevice, router, provider and edge, with where NAT applies.

Network & IP

Traceroute

See every router between a probe and a host, grouped by the network that runs it, with delay and loss at each hop. Traces run from real probes worldwide, and the results explain which stars and spikes are normal and which point to a real problem.

  • PathNetworks crossedEach hop grouped by the AS that runs it.
  • LatencyDelay by hopWhere delay starts, and whether it stays.
  • LossLoss that mattersLoss that continues to the target, told apart from rate-limited replies. Three probes per hop are a snapshot.
  • ProbesFrom anywhereA continent, a country, or three at once.

Network & IP

Ping

Ping a host from probes around the world and see how fast it answers from each place. A latency chart shows the fastest, average and slowest reply per location, with packet loss and jitter, and TCP connect for hosts that ignore ping.

  • RTTRound-trip timeFastest, average and slowest reply from each probe.
  • LossPacket lossPackets that never got an answer, per location.
  • JitterStabilityHow much replies vary from one to the next.
  • TCPTCP connectTime a port’s handshake when ICMP is blocked.

Network & IP

IP WHOIS Lookup

Find out who an IP address or network is registered to. The lookup asks whichever regional registry holds it, ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC, and draws the allocation path from IANA down to the network, with its abuse contact.

  • HolderRegistered toThe organization, network name, range and type.
  • PathAllocation pathIANA to the registry to the network, drawn to scale.
  • AbuseContactsAbuse, technical and network operations contacts.
  • BGPAnnounced byThe AS that routes the address today.

Network & IP

ASN Lookup

Look up an AS number, IP address, prefix or domain to see which network announces it, who runs that network, the address space it routes and the networks it connects to. A graph shows its upstreams and downstreams from public BGP data.

  • OwnerWho runs itHolder, country, registry and allocation date.
  • RouteOrigin and RPKIThe prefix an IP is announced in, and whether a ROA covers it.
  • PrefixesAddress spaceIPv4 and IPv6 prefixes, by size.
  • PeersConnectionsUpstream and downstream networks in BGP paths.

Browse by category

Guides and support

Email & authentication

How a domain sends, receives and protects its mail.

Network & IP

Reachability, addressing and the paths between networks.

Domains & DNS

The main tools, also in the header.