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 authentication

Tools to verify and validate your email authentication setup.

Syntax validation

Record inspectors

Generators

Deliverability

Email deliverability audit Mail header analyzer Email tester IP Blacklist Checker Domain Blacklist Checker SPF Flattener DKIM Selector Finder SMTP/MX Tester DMARC report reader TLS-RPT Report Reader

Hosting

MTA-STS hosting BIMI Hosting TLS-RPT Monitoring DMARC Monitoring

IP tools

Quickly inspect an IP address or your own connection.

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.

Web & Certificates

BIMI logos, VMC/CSR certificates and web page diagnostics.

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.

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

SEO

Search engine optimization, Google indexing, crawl budget and technical SEO tips.

3 articles

February 2026

Chart showing the evolution of median web page weight from 2010 to 2025

CaptainDNS · February 12, 2026

Median web page weight in 2025: 15 years of web bloat

The median web page weight has grown 5x in 15 years. HTTP Archive data, resource breakdown by type, SEO impact, and projections for 2026-2028.

Crawl budget: diagram of crawl rate limit and crawl demand

CaptainDNS · February 11, 2026

Crawl budget: understanding and optimizing how Google crawls your site

Crawl budget determines how many pages Googlebot explores on your site. Learn how to analyze it, optimize it, and avoid common pitfalls.

Googlebot's 2 MB crawl limit: HTML truncation diagram

CaptainDNS · February 10, 2026

Googlebot's 2 MB Crawl Limit: What Happens When Your Pages Are Too Heavy

Google only crawls the first 2 MB of a page's HTML source. Beyond that, content is truncated and never indexed. Here's what it means for your SEO.