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CaptainDNS

Propagation & diagnostics

Compare resolvers worldwide and inspect returned answers.

Email authentication

Tools to verify and validate your email authentication setup.

SPF syntax validator

Review include chains and DNS query limits before publishing changes.

SPF record inspector

Resolve the published TXT record, flag lookup limits and decode each mechanism.

DKIM syntax validator

Quickly check the syntax of your DKIM records.

DKIM record check

Resolve a selector and analyse the published DKIM TXT record.

DMARC syntax validator

Check rua/ruf destinations, alignment modes and the active policy before publishing.

DMARC record inspector

Resolve the published policy, surface diagnostics and confirm enforcement before switching to reject.

BIMI syntax validator

Validate BIMI tags, the logo fetch and the VMC certificate before publishing.

BIMI record inspector

Resolve the published BIMI record, inspect logo and VMC diagnostics in one place.

Email deliverability audit

Audit MX, SPF, DKIM and DMARC to confirm a domain is ready to send.

Mail header analyzer

Decode participants, authentication results and routing from raw headers.

DMARC record generator

Create compliant DMARC records with all policy and reporting options.

Text

Transform, encode and measure your content in seconds.

Text case converter

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

Base64 encoder / decoder

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

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.

Images

Preview and validate your BIMI logos before publishing.

BIMI logo lookup

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

Certificates

Inspect CSRs, BIMI logos and VMC certificates before you deploy.

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.

IP

Look up addresses, owners, reverse records and ranges.

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.

My IP address

Detect your IPv4/IPv6 addresses and their geolocation.

Certificate tools

Security-minded utilities for certificate and brand workflows

Explore the specialised helpers that sit alongside DNS diagnostics: certificate parsers, BIMI validation helpers, and upcoming automation around trust chains.

CSR parser

Decode certificate signing requests, extract subject attributes and fingerprints before you sign.

VMC inspector

Audit a Verified Mark Certificate to confirm issuer, validity window, and certified domains before publishing BIMI records.

Why focus on certificate workflows

Inspect CSR payloads before signing

Uploading a CSR to your CA without double-checking its attributes often leads to rejected certificates. The CSR parser reveals the subject data, SAN entries, and fingerprints before submission so that the change ticket can be validated in one pass.

Validate BIMI certificates in minutes

Brand Indicators for Message Identification rely on Verified Mark Certificates. The inspector confirms that the PEM or hosted certificate matches your legal entity, that the SAN entries list the correct domains, and that the chain is still valid.

What comes next

Additional helpers will join this space soon: automated CSR linting, trust-store comparisons, and diff tools to check renewals. Each utility keeps the processing within the CaptainDNS perimeter to preserve confidentiality by default.