DNS tools: query and trace your zones
CaptainDNS DNS tools let you query any record on any domain. Choose the query type (A, AAAA, MX, TXT, CNAME, NS, SOA, CAA, SRV, PTR), protocol (UDP, TCP, DoH), and 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 measured latency. This view quickly identifies a failing server or stale cache.
Propagation tracking compares responses from 18 public resolvers around the world. Visualize differences between regions and detect inconsistencies before they affect your users.
IP tools: reverse lookup, WHOIS, and geolocation
The IP category includes three complementary tools. 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 holder, address block, and ASN.
The IP address detector identifies your own public IP and displays its geolocation along with your ISP. Useful for verifying VPN exit point or diagnosing routing issues.
Email authentication: SPF, DKIM, DMARC, and BIMI
Email authentication protects your domain from spoofing and improves message deliverability. CaptainDNS provides dedicated analyzers for each protocol.
The SPF tool checks your record syntax, counts mechanisms, and flags exceeding the 10-lookup limit. The DKIM tool verifies selector presence and public key length. The DMARC analyzer examines alignment (strict or relaxed) and applied policy (none, quarantine, reject).
A DMARC generation assistant guides you to create a compliant record with proper rua and ruf addresses to receive your reports. Finally, the BIMI analyzer verifies presence and consistency of your record before publishing.
Access email authentication tools →
Text tools: conversion, encoding, and counting
Text utilities run entirely in your browser. No data is sent to our servers.
The case converter instantly transforms your text to uppercase, lowercase, Title Case, or Sentence case. The Base64 encoder/decoder converts plain text to Base64 and back. The slug generator produces URL-friendly strings from any title. The character counter displays character, word, sentence, and paragraph counts.
Certificate tools: CSR and VMC
Before submitting a certificate request, validate your CSR with the dedicated analyzer. The tool extracts subject, Subject Alternative Names (SANs), signature algorithm, and key size for verification.
The VMC (Verified Mark Certificate) analyzer decodes the certificate used for BIMI. It displays the full trust chain, validity period, and holder information.
Image tools: BIMI validation
The BIMI logo validator checks that your SVG file meets email client technical requirements. It verifies Tiny-PS profile, dimensions (square recommended), file size, and SVG code compliance.
A non-compliant logo won't display in Gmail, Yahoo Mail, or other BIMI-compatible clients. Always validate before publishing your BIMI record.
HTTP tools: page analysis and crawl budget
CaptainDNS HTTP tools let you analyze your web pages from a search-engine perspective. The Page Size Checker measures the actual size of your page as Googlebot downloads it, distinguishing raw HTML from total resources.
Googlebot enforces a 2 MB limit on the HTML it indexes. Beyond that, content is truncated and tags at the end of the page (internal links, structured data, text content) are ignored. The tool simulates this truncation and identifies exactly which elements would be lost.
Choose from several User-Agents (Googlebot Desktop, Googlebot Mobile, Bingbot, standard browser) to compare server responses and detect potential content or behavior variations.