How it works
How DNS Previewer works
When you migrate a site to a new host, your domain still points to the old server until you update DNS. That’s a problem: you can’t easily test the new host under its real domain, and a botched switchover is visible to every visitor. Once you do switch, the old address can hang around in caches for hours, which is covered in how long DNS propagation really takes.
The usual way
Without DNS Previewer
Switch first, find out later.
- 1
Copy your site to the new server
Files, database and SSL certificate. - 2
Switch DNS and hope
There’s no easy way to see the new server under your real domain first. - 3
Wait for DNS to update
Often hours, depending on the TTL on your DNS record. Find the problems live
Your visitors spot them before you do.
Rolling back means another DNS change and another wait
The safe way
With DNS Previewer
Check first, switch when it works.
- 1
Copy your site to the new server
Same as before. Your live site stays put. - 2
Generate a preview link
Enter your domain and the new server’s IP address. - 3
Check it in your browser
Your real domain, served from the new server. Send it to a client or open it on your phone. Everything works? Switch DNS
Visitors go straight to a working new site.Generate a preview link
The standard workarounds, and why they hurt
- Editing /etc/hosts: only works on your machine. Can’t share with clients or QA. More on where the hosts file falls short, and where the Windows hosts file lives if you still need it.
- Using the server’s IP directly: wrong Host header, SSL cert errors, broken vhosts.
- Staging subdomain: often has a different code path than production, so issues slip through.
What DNS Previewer does
- You tell us your domain (
example.com) and the new server’s IP or hostname. - We generate a short subdomain like
a7xk2p.dnspreviewer.comand open a reverse proxy on it. - When you visit that URL, our proxy connects to your target server using the correct
Hostheader and TLS SNI for your domain, so your server serves the right vhost and content. - Responses are streamed back to your browser. HTML and CSS that reference your domain are rewritten to the preview URL so clicks and assets keep working inside the preview.
- After 15 minutes the session expires and the URL returns a friendly expired page.
What’s stripped or rewritten
X-Frame-Options,Content-Security-Policy, andStrict-Transport-Securityheaders are removed so the preview can load.Set-Cookiedomain attributes are removed so cookies bind to the preview subdomain.Locationredirects to your domain are rewritten to stay inside the preview.- Response bodies are decompressed before rewriting (we ask upstream for identity encoding).
Known limitations
- JavaScript that hardcodes your apex domain in
fetch()/XMLHttpRequestwill hit CORS errors. This is inherent to any preview proxy. - WebSockets are not proxied. Most apps fall back to long polling.
- Responses larger than 4 MB pass through without link rewriting.
- Third-party services (OAuth, payment gateways) may not accept requests that originated from a subdomain they don’t recognize.
Moving a WordPress site? The preview covers the “does it work under the real domain” part. The rest is in the WordPress migration checklist. If you’re weighing this up against the paid option, here’s an honest comparison with SkipDNS.