A comprehensive suite of Free tools for keeping sites, networks, and email healthy

See which certificate authorities are allowed to issue for your domain.

Look up A, AAAA, MX, TXT, NS, and CNAME records for any domain.

Check a DNS record across multiple public resolvers and spot mismatches.

Validate your domain's chain of trust and spot broken signatures.

List a domain's NS records and check the delegation agrees.

Find the hostname an IP address points back to.

Read a zone's serial, refresh, retry, and expiry timers.

Confirm your brand logo and VMC are published for inbox display.

See if a domain or IP is on major email blacklists.

Look up a DKIM key by selector and confirm it's published correctly.

Read your domain's DMARC policy, alignment, and reporting addresses.

Check a domain's SPF, DMARC, MX, and (optionally) DKIM records.

Paste raw headers to map delivery hops, delays, and SPF/DKIM/DMARC results.

Check an address's syntax and that its domain can actually receive mail.

Validate your MTA-STS DNS record and policy file for enforced TLS mail.

List a domain's mail servers and confirm the primary answers on SMTP.

Check a mail server's banner, STARTTLS support, and open-relay exposure.

Expand your sending sources, validate syntax, and count DNS lookups.

Confirm your SMTP TLS reporting record is set correctly.

Read an SSL/TLS certificate's subject, issuer, validity, and SANs.

Read the subject, key details, and SANs inside a certificate signing request.

Verify your Strict-Transport-Security header and preload eligibility.

Find insecure HTTP resources loaded on your HTTPS pages.

Grade a site's HSTS, CSP, X-Frame-Options and more, A–F, with fixes.

See a host's TLS certificate issuer, validity dates, and days until it expires.

Verify the full certificate chain, not just the leaf — catch missing intermediates.

See which TLS versions a host supports and grade its configuration.

Find the autonomous system, network owner, and prefixes behind any IP.

Find a domain's registration date and how long it's been established.

Find the country, city, ISP, ASN, and hostname behind any IP address.

See your public IP address and request details.

Check whether a host or device responds to ICMP ping, and how fast.

Test whether a TCP port (SMTP, POP3, FTP, …) is open on a host.

Check which common ports are open, closed, or filtered on a host.

Network, broadcast, mask, host range, and host count for any CIDR.

Registrar, registration & expiry dates, and nameservers for any domain.

Confirm your server compresses responses with gzip or Brotli.

See all response headers and which security headers are present.

Check any URL's HTTP status code, response time, redirects, and headers.

See which modern HTTP protocols your server negotiates.

See your page's title, description, and social cards as platforms render them.

Follow a URL's full redirect chain, hop by hop.

Fetch and validate robots.txt and test whether a URL is allowed.

Check your XML sitemap is well formed, reachable, and within limits.

Measure time to first byte and total response time.

Convert text to and from Base64, instantly in your browser.

Translate a cron schedule into plain English and see the next run times.

Generate MD5, SHA-1, and SHA-256 checksums, in your browser.

Convert IPv4/IPv6 between dotted, decimal, hex, and binary.

Beautify, minify, and validate JSON, in your browser.

Decode a JSON Web Token's header and payload, in your browser.

Identify the hardware vendor behind a MAC address from its OUI.

Build strong random passwords and test strength, in your browser.

Test regular expressions against sample text with live matches.

Convert between Unix time and human-readable dates.

Convert text to and from percent-encoding, in your browser.

Break a user-agent string into browser, OS, and device.

Generate random version 4 UUIDs, one or many, in your browser.