DNS tools: lookup, audit, propagation, DNSSEC and RDAP
The CaptainDNS DNS tools let you query any record on any domain. You choose the query type (A, AAAA, MX, TXT, CNAME, NS, SOA, CAA, SRV, PTR), the protocol (UDP, TCP, DoH), and the resolvers to use.
The iterative trace reconstructs the complete path of a query: root servers, TLD, then authoritatives. Each step displays the response received and the measured latency, which quickly identifies a failing server or a stale cache.
The propagation test, now a separate tool from DNS lookup, compares the responses obtained from public resolvers around the world. You visualize the differences between regions and detect inconsistencies before they affect your users.
Beyond resolution, the DNS health audit checks parent/zone consistency, delegation and SOA synchronization, the DNSSEC Checker validates your chain of trust, and the RDAP Lookup queries the domain's registration data (registrar, dates, EPP codes), with automatic WHOIS fallback.
IP tools: PTR, WHOIS, geolocation and subnet calculations
The IP category brings together five complementary tools. The PTR reverse lookup finds the hostname associated with an IPv4 or IPv6 address. IP WHOIS queries the five RIRs (ARIN, RIPE, APNIC, LACNIC, AFRINIC) to display the holder, the address block, and the ASN.
The IP address detector identifies your public IPv4 and IPv6 addresses and displays their geolocation along with your internet service provider. Handy for checking a VPN exit point or diagnosing a routing issue.
Finally, the IPv4 netmask calculator determines the network address, broadcast, wildcard, and number of usable hosts, while the IPv6 subnet calculator details the prefix, address range, and reverse DNS (ip6.arpa).
Email authentication: SPF, DKIM, DMARC, BIMI, MTA-STS, TLS-RPT and DANE
Email authentication protects your domain against identity spoofing and improves the deliverability of your messages. With more than 35 tools, CaptainDNS covers every protocol, on both the sending and the receiving side.
For each protocol, a syntax validator checks a raw record and an inspector resolves it live from the Internet. The SPF analyzer counts mechanisms and flags any breach of the 10 DNS lookup limit, the DKIM tool verifies selector presence and key length, and the DMARC analyzer examines alignment (strict or relaxed) and the applied policy (none, quarantine, reject).
Generators build your records ready to publish: SPF generator from your email providers, DKIM generator with key pair and TXT record, DMARC assistant, then BIMI, MTA-STS, TLS-RPT and DANE/TLSA. The BIMI inspectors and the MTA-STS, TLS-RPT and DANE tools secure transport and visual identity.
Finally, the security and deliverability audit analyzes in a single scan both the sending side (SPF, DKIM, DMARC, BIMI) and the receiving side (MX, MTA-STS, DANE, TLS-RPT, DNSSEC), and returns a score out of 100. Blacklist checkers, the SMTP/MX tester, and DMARC/TLS-RPT monitoring round out the diagnosis.
Access email authentication tools →
Text tools: conversion, encoding, security and formatting
Text utilities send your input to the CaptainDNS API, which returns the result and retains no content.
The case converter transforms your text to uppercase or lowercase. The Base64 encoder/decoder and the URL encoder/decoder (percent-encoding) prepare your payloads, secrets, and query strings. The slug generator produces clean URLs, and the word and character counter measures the length of an email subject or a TXT record.
On the security and development side, the password generator creates passwords and passphrases with an entropy indicator, the hash generator computes MD5, SHA-1, SHA-256 and SHA-512, the regex tester (RE2 syntax) visualizes matches and capture groups, and the JSON/YAML formatter validates and converts your documents.
Certificate tools: SSL checker, CSR and VMC
The SSL Certificate Checker opens a TLS connection to a server and returns a verdict on the certificate it presents: validity, days left before expiry, complete chain of trust or missing intermediate, and hostname match against the SAN entries.
Before submitting a certificate request, validate your CSR with the CSR parser. The tool extracts the subject, the Subject Alternative Names (SANs), the signature algorithm, and the key size for verification.
The VMC certificate analyzer (Verified Mark Certificate) decodes the certificate used for BIMI. It displays the full trust chain, the validity period, and the holder information.
Image tools: BIMI logo validation and conversion
The BIMI logo validator checks that your SVG file meets the technical requirements of email clients. It verifies the Tiny-PS profile, the dimensions (square recommended), the file size, and the compliance of the SVG code.
When the report flags forbidden elements, the BIMI SVG converter clears them for you. Scripts, external fonts and animations are removed, and the version, baseProfile and title attributes required by Tiny-PS are added. The tool lists every change before you download the file.
A non-compliant logo will not display in Gmail, Yahoo Mail, or the other BIMI-compatible clients. Always validate before publishing your BIMI record.
HTTP tools: crawl, security, redirects, uptime and status pages
The CaptainDNS HTTP tools cover the entire lifecycle of your URLs, from SEO to availability. The page crawl checker measures the weight of the HTML as Googlebot downloads it, simulates truncation beyond 2 MB (where internal links, structured data, and end-of-page content would be ignored), and inventories the sub-resources that weigh on your crawl budget.
On the security side, the HTTP headers analyzer grades your headers (CSP, HSTS, X-Frame-Options...) from A to F, and the HSTS test verifies eligibility for the Chrome preload list. The redirect checker unfolds redirect chains and shortened links, while the phishing URL checker compares a URL against three threat intelligence databases.
For operations, redirect hosting routes your domains over HTTPS with a managed TLS certificate, the uptime monitor probes your endpoints every 5 minutes from Europe (US/APAC option depending on the plan) with email and webhook alerts, and public status pages communicate the state of your services to your users with no DNS setup.