Observatory Blog

CaptainDNS

DNS Lookup

Choose a DNS record type to search for.

Propagation & diagnostics

Compare resolvers worldwide and inspect returned answers.

Propagation testPublic resolvers, remaining TTLs, divergent responses.
Domain DNS auditParent/local NS, authority and response times.
DNSSEC CheckerValidate chain of trust, DS records and signing keys.
API & integrations
Keep history, monitor your zones and automate recurring checks.

Email Diagnostics

Tools to verify and validate your email authentication setup.

Syntax validation

Record inspectors

SPF

SPF syntax validator

SPF record inspector

DKIM

DKIM syntax validator

DKIM record check

DMARC

DMARC syntax validator

DMARC record inspector

BIMI

BIMI syntax validator

BIMI record inspector

MTA-STS

MTA-STS syntax validator

MTA-STS record inspector

TLS-RPT

TLS-RPT syntax validator

TLS-RPT record inspector

DANE / TLSA

DANE TLSA syntax validator

DANE TLSA Checker

Deliverability

Email deliverability audit Mail header analyzer Email tester IP Blacklist Checker Domain Blacklist Checker SPF Flattener DKIM Selector Finder SMTP/MX Tester

Secure & Monitor

Record generators, policy hosting and continuous monitoring.

Generators

SPFSPF record generator DKIMDKIM generator DMARCDMARC record generator BIMIBIMI record generator MTA-STSMTA-STS generator TLS-RPTTLS-RPT generator DANEDANE TLSA generator

Hosting

MTA-STSMTA-STS hosting BIMIBIMI Hosting

Monitoring

TLS-RPTTLS-RPT Monitoring DMARCDMARC Monitoring

Report readers

DMARCDMARC report reader TLS-RPTTLS-RPT Report Reader

Network & Web

Network tools, web page analysis and certificates.

IP Tools

My IP address

Detect your IPv4/IPv6 addresses and their geolocation.

Reverse lookup

Resolve a PTR record and validate DNS consistency.

IP WhoIs

Identify the owner of an IP range and its contacts.

IPv4 netmask

Calculate network, broadcast and usable hosts for any IPv4 block.

IPv6 subnet calculator

Calculate IPv6 subnets, address ranges and reverse DNS entries.

Web & Certificates

BIMI logo lookup

Inspect a BIMI logo URL - format, metadata and live rendering - before rollout.

BIMI SVG converter

Convert any SVG to BIMI-compliant Tiny-PS format in seconds.

CSR parser

Inspect a CSR, extract subject details, fingerprints and requested SANs.

VMC inspector

Inspect a Verified Mark Certificate - issuer, validity and SAN coverage - before you publish BIMI.

Page size checker

Check if your page exceeds Google's 2 MB crawl limit.

Phishing URL Checker

Check if a URL is flagged as phishing or malware by 4 threat intelligence sources.

Domain Redirect

Redirect your domains with automatic HTTPS and 301/302 redirects.

Developer Tools

Text utilities and tools for everyday dev work.

Text

Transform and measure your content in seconds.

Text case converter

Convert any block of text to upper or lower case instantly.

Slug generator

Transform any sentence into an SEO-friendly slug in seconds.

Word & character counter

Measure the length of any text, with instant word and character counts.

Password generator

Generate strong random passwords and memorable passphrases instantly.

Developer

Encoding, hashing, regex and formatting for everyday dev work.

Base64 encoder / decoder

Encode or decode any content in Base64 without leaving the browser.

Hash Generator

Compute MD5, SHA-1, SHA-256 and SHA-512 hashes of any text.

URL encoder / decoder

Encode or decode text using percent-encoding (RFC 3986) right in your browser.

Regex Tester

Test a regular expression against text and visualize matches.

JSON / YAML Formatter

Format, validate and convert JSON and YAML in one click.

New tools

100% free

MTA-STS & BIMI hosting, DMARC & TLS-RPT monitoring

CaptainDNS hosts your MTA-STS policy and BIMI logo, and monitors your DMARC and TLS-RPT reports automatically. All free, no server required.

Google, Yahoo and Microsoft now require stronger email authentication. Protect your deliverability in just a few clicks.

MTA-STS BIMI TLS-RPT DMARC Monitoring

HTTP

HTTP protocol, redirects, status codes, HTTPS and web best practices.

2 articles

March 2026

Comparative diagram of 301 and 302 redirects showing SEO impact, PageRank transfer and domain migration checklist

CaptainDNS · March 16, 2026

301 vs 302 redirect: understand the differences, SEO impact and succeed with your domain migration

301 permanent or 302 temporary? Understand the SEO impact of each code, avoid common mistakes and follow our domain migration checklist.

Diagram showing a vanity URL captaindns.com redirected to a landing page with click counter and QR code

CaptainDNS · March 16, 2026

Vanity URLs, link tracking and QR codes: the complete guide to marketing redirects

Create memorable branded links, track clicks and measure offline-to-online traffic with smart redirects.