A wildcard DNS A record is a catch-all — it resolves any subdomain that does not have its own explicit record to a single IP address. Set *.example.com and suddenly anything.example.com responds. Convenient for some use cases, but potentially damaging for SEO if you do not understand the consequences.
What Wildcard A Records Do
A wildcard A record uses an asterisk as a placeholder in DNS. Any subdomain not explicitly defined inherits this record. If a user or a crawler requests random.example.com, the wildcard resolves it to your server. What happens next depends entirely on how your server handles that request.
Why This Causes SEO Problems
Duplicate Content at Scale
If your server returns the same content for any subdomain — which is the default behaviour for many configurations — you now have infinite URLs serving identical pages. Search engines may index abc.example.com, xyz.example.com, and test.example.com as separate pages, all competing with your main site for rankings.
Crawl Budget Waste
Search engines allocate a finite crawl budget to each domain. Wildcard subdomains can cause crawlers to spend that budget indexing thousands of duplicate or meaningless URLs instead of the pages that matter. For large sites, this is a real problem — your important product pages or blog posts get crawled less frequently while bots chase phantom subdomains.
Link Equity Dilution
Any backlinks pointing to wildcard subdomains scatter your domain’s authority across URLs that should not exist. Instead of consolidating ranking signals on your primary domain, you bleed equity into pages that add no value.
Keyword Cannibalisation
Multiple subdomains serving the same or similar content can compete for the same keywords. Search engines must choose which version to rank, and they often choose poorly — or suppress all of them.
When Wildcards Are Appropriate
Wildcard records make sense for specific use cases: multi-tenant SaaS platforms where each customer gets a subdomain, development and staging environments (with proper noindex directives), or CDN configurations. Outside these scenarios, explicit DNS records for each subdomain are safer.
Fixing the Problem
Use Explicit Records
Define individual A records for every subdomain you intend to use. Remove the wildcard unless you have a specific technical need for it.
Configure Server-Side Handling
If you must keep a wildcard, configure your server to return a 404 for unrecognised subdomains instead of serving content. Alternatively, redirect all wildcard subdomains to your primary domain with a 301.
Implement Canonicalisation
Add canonical tags pointing to your preferred URLs. This tells search engines which version of a page is authoritative, mitigating duplicate content issues from wildcard subdomains.
Monitor Indexed URLs
Use Google Search Console to check for indexed subdomains you did not create. If wildcard subdomains are appearing in search results, address them immediately with redirects or removal requests.
DNS configuration is infrastructure, but it has direct SEO consequences. If your hosting setup includes wildcard records, audit the impact before it quietly erodes your search visibility.