Skip to main content
Log in
CaptainDNS

Email Diagnostics

Tools to verify and validate your email authentication setup.

SPF
DKIM
DMARC
DMARCbis
BIMI
MTA-STS
TLS-RPT
DANE / TLSA

Deliverability

Email deliverability auditMail header analyzerEmail testerIP Blacklist CheckerDomain Blacklist CheckerSPF FlattenerDKIM Selector FinderSMTP/MX Tester

Secure & Monitor

Record generators, policy hosting and continuous monitoring.

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.

Certificates & BIMI

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.

Web

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.

Redirect Checker

Analyze HTTP redirect chains

Domain Redirect

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

HTTP Uptime Monitor

Monitor your sites with scheduled HTTP checks and email alerts.

Status Pages

Publish a public status page grouping your HTTP monitors.

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.

Public API changelog

This page lists the major changes to the CaptainDNS public API. Non-breaking additions (new endpoints, new optional fields) are documented here without formal notice. Breaking changes are announced at least 30 days before deployment, on this very page and by email to active key holders.

Versioning policy

  • Backward compatibility: adding optional fields and new endpoints does not break existing clients.
  • Deprecations: a deprecated field or endpoint stays functional for at least 6 months after the announcement.
  • Breaks: breaking changes are announced 30 days ahead and deployed under a new versioned URL (for example /public/v2/*). The V1 URL stays up during the migration window.
  • Version identifier: the OpenAPI spec carries its own version (info.version). The major number follows the versioned URL, the minor number follows backward-compatible additions.

Version 0.2.0 - 2026-04-09

Added

  • 40+ public endpoints under /public/v1/* covering DNS, mail, web and text:
    • DNS: resolve, resolve/propagation, dnssec/check, ip/whois, ip/nslookup, ip/netmask, rdap/lookup, domain/dns-check.
    • Mail: spf/lookup, spf/validate, dkim/lookup, dkim/validate, dmarc/lookup, dmarc/validate, dmarc/generate, dmarcbis/check, dmarcbis/migrate, dmarc/report/analyze, bimi/lookup, bimi/validate, bimi/logo/lookup, mta-sts/lookup, tls-rpt/lookup, dane/lookup, blacklist/ip, smtp/check, mail/header-audit, mail/header-analyze, mail/domain-check, deliverability/score, certificates/csr/parse, certificats/bimi/parse, certificats/bimi/lookup.
    • Web: url/check, page/crawl-check, phishing/check.
    • Text: text/lower, text/upper, text/stats, text/slug, text/base64/encode, text/base64/decode, text/password/generate, text/urlencode, text/urldecode, text/json/format, text/json/to-yaml, text/yaml/format, text/yaml/to-json, text/hash, text/regex/test.
  • API key management from the CaptainDNS dashboard: list, create, revoke, rotate and consult usage.
  • OpenAPI schema PublicAPIError with 10 canonical codes for all public API errors.
  • Stripe-style Idempotency-Key header, 24-hour replay, 409 IDEMPOTENCY_CONFLICT on divergent body.
  • Headers X-Credits-Limit/Remaining/Consumed returned on every successful response.
  • Headers RateLimit, RateLimit-Policy, X-RateLimit-Limit/Remaining/Reset (IETF draft + X-prefixed).
  • Header X-Request-Id returned on every response to ease support.
  • 5 billing plans: Free, Starter, Pro, Business, Enterprise, with per-tier quotas and overage billing.
  • Opt-in overage billing with configurable monthly budget cap from the dashboard.
  • Automatic leak detection via the GitHub secret scanning program.

Not shipped in V1

  • Webhooks: planned for V2.
  • Official SDKs: the Speakeasy TypeScript SDK is planned for the first delivery.
  • mTLS for Business and Enterprise plans: deferred.

Stay up to date

  • CaptainDNS blog: major releases are relayed in dedicated posts on captaindns.com/en/blog.
  • Email: active key holders receive an automatic notification for any breaking change.
  • This page: any addition or fix is recorded here, latest first.
  • OpenAPI specification: the info.version field is bumped on each release. Watching its value lets you trigger SDK regenerations.

Next step: go back to the quickstart to start integrating, or explore the OpenAPI reference to see all schemas in detail.