The Short Version
MxToolbox is the go-to toolbox for one-off lookups: MX, DNS, SPF, DMARC, blacklists and dozens more, free in your browser. Its paid Delivery Center plans focus on email deliverability (inbox placement tests, DMARC reporting, blacklist monitoring) and are listed at $129/month and $399/month on MxToolbox's own plan page.
DomainCat is built for the other half of the job: keep watching a list of domains and tell me before something expires or breaks. SSL certificates (including the origin cert behind Cloudflare), domain registration expiry, DNS, SPF/DKIM/DMARC records, blacklists and security headers, on every domain, every 6 hours. Plans start free, then $12/month.
If your main problem is email landing in spam, MxToolbox's deliverability tools are the better fit. If your problem is "a cert or domain expired and nobody noticed", that's exactly what DomainCat is for.
Side by Side
Prices as listed by each vendor, November 2026. Check mxtoolbox.com for their current plans.
| DomainCat | MxToolbox | |
|---|---|---|
| Best at | Ongoing monitoring + expiry alerts for many domains | One-off lookups; email deliverability (paid) |
| Free tier | 5 domains monitored every 6 hours, email alerts | Free browser lookups |
| Paid entry price | $12/mo (50 domains) · $120/yr | Delivery Center $129/mo |
| SSL certificate expiry alerts | Yes, 30 / 14 / 7 days, then daily | Lookup tools; not the focus of Delivery Center |
| Origin cert behind Cloudflare | Yes, monitored separately from the edge cert | No |
| Domain registration expiry alerts | Yes (Pro and MSP) | WHOIS lookup tool |
| SPF / DKIM / DMARC | Record checks on every domain | Lookups + DMARC report processing (paid) |
| Blacklist monitoring | Yes, alerts on Pro and MSP | Yes (paid) |
| Inbox placement testing | No | Yes (paid) |
| DNS / WHOIS / header change alerts | Yes (MSP) | See MxToolbox plans |
| Alert channels | Email, Slack, Teams, webhooks, PagerDuty | See MxToolbox plans |
| Ask your AI assistant | Yes: built-in MCP server, listed in Claude's connector directory | No |
| Unlimited domains | $29/mo (MSP) | See MxToolbox plans |
Where MxToolbox Is the Better Choice
We'd rather you pick the right tool than the wrong one from us. MxToolbox is stronger if you need:
- Inbox placement testing: seeing whether your campaigns land in Gmail or Outlook spam folders
- DMARC aggregate report processing and visualization for a sending domain
- A huge library of one-off diagnostic lookups in one place
Where DomainCat Fits Better
DomainCat is the better fit when the job is keep watching a list of domains and warn me in time:
- You manage dozens of domains (yours or your clients') and need expiry alerts, not lookups
- Your sites sit behind Cloudflare and you need to know when the origin cert expires, not just the edge cert
- You want SSL, domain registration, DNS, email authentication and blacklists in one dashboard
- You're an MSP: group domains by client, and send alerts straight to the person who owns the cert
- You'd like to ask Claude, Cursor or VS Code "what expires this month?" and get a real answer
- You want to pay $12 or $29 a month, not $129+
Certificates Are Expiring Faster Now
Public TLS certificates can now last at most 200 days (since March 15, 2026), and the CA/Browser Forum schedule takes that down to 47 days by 2029. Let's Encrypt also stopped sending expiry reminder emails in 2025. More renewals and fewer reminders means more chances for one to slip. An occasional manual lookup doesn't catch that; a monitor does.
Try It Without Signing Up
Our free domain health checker runs the same checks DomainCat monitors (SSL, WHOIS expiry, DNS, SPF/DMARC, blacklists and security headers) on any domain or IP, with no login. Like what you see? One click turns it into a monitor.