What this is
A toolbox for the questions that come up when a domain misbehaves: what a record actually resolves to, whether mail from it can be authenticated, what a server sends back, and whether an address is reachable.
Every lookup runs against the public resolvers directly rather than through this server's DNS cache, so a domain you moved ten minutes ago reads as moved.
Install our MCP
Claude, Cursor and other AI assistants can run these checks for you and read the findings. How to install it, and what it provides.
DNS7 tools
| Check Domain | See whether a domain resolves, and to what. |
| DNS Records | Every record type for a domain, or the PTR for an IP. |
| DNS Propagation | Compare what five public resolvers currently answer. |
| DNSSEC Checker | Keys, the DS at the registrar, and whether they agree. |
| CAA Records | Which certificate authorities may issue for a name. |
| Bulk Reverse DNS | PTR records for a whole IPv4 range at once. |
| WHOIS Lookup | Registrar, dates and name servers from the registry. |
Email9 tools
| Email Health Check | MX, SPF, DKIM and DMARC for a domain, graded. |
| SPF Validator | Counts the DNS lookups your SPF record really costs. |
| DMARC Checker | Read a published DMARC record tag by tag. |
| MTA-STS & TLS-RPT | Policy record, policy file and the MX hosts it covers. |
| BIMI Checker | Logo record, certificate and the DMARC it needs. |
| Email Validator | Syntax, MX, role accounts and disposable providers. |
| SPF Generator | Build an SPF record from senders you trust. |
| DKIM Generator | Turn a public key into the TXT record to publish. |
| DMARC Generator | Build a DMARC policy with reporting addresses. |
HTTP9 tools
| Check Website | Status code, response time and the redirect chain. |
| HTTP Headers | Every response header, with a security grade. |
| SSL Checker | Certificate dates, names, protocol and cipher. |
| Meta Tags & Open Graph | What a page tells search engines and chat apps. |
| robots.txt Checker | Crawler rules, and whether the sitemaps exist. |
| security.txt Checker | Where to report a vulnerability, per RFC 9116. |
| TLS Versions | Which protocol versions a server still accepts. |
| Certificate Decoder | Read a pasted PEM certificate or CSR. |
| Certificate Chain | The full chain a server sends, leaf to root. |
Network2 tools
| Port & Latency | TCP connect time to the ports that matter. |
| Blacklist Check | Look an address up in six mail blocklists. |
Utilities12 tools
| Subnet Calculator | Network, broadcast, mask and host range from a CIDR. |
| Base64 | Encode and decode, including URL-safe Base64. |
| Punycode | Convert between Unicode and ASCII domain names. |
| JWT Decoder | Read the header and claims of a token. |
| Hash Generator | MD5, SHA-1, SHA-256, SHA-512 and CRC32 at once. |
| UUID Generator | Random v4 or time-ordered v7 identifiers. |
| Password Generator | Random passwords, and bcrypt for an htpasswd file. |
| Timestamp Converter | Unix time to a date and back, in any timezone. |
| URL Encoder | Percent-encode, decode, and split a URL apart. |
| JSON & YAML | Validate, pretty-print, minify and convert. |
| Cron Checker | What an expression means, and when it next runs. |
| What Is My IP | Your address, its PTR and what your browser sends. |
Something missing?
If a tool you need is not here, suggest it.