01 The Rule
Use subdirectories (/blog, /products) for content that should inherit the domain's authority. Use subdomains only for functionally separate applications (app.domain.com) that don't need to share SEO signals with the main domain.
Subdomain vs. Subdirectory
Last updated: 2025-08-15
02 Rationale
Google treats subdomains as semi-separate entities. Link equity, topical authority, and crawl budget are not fully shared between subdomains. Moving content from subdirectory to subdomain typically results in temporary or permanent traffic loss.
03 Implementation
- Default to subdirectories for blog, shop, docs, and content sections
- Use subdomains only for truly separate applications (SaaS app, CDN, API)
- If migrating from subdomain to subdirectory, use 301 redirects and monitor
- Verify Search Console properties for both subdomain and root domain
- Ensure internal links between subdomain and main domain use proper linking
04 Common Violations & Consequences
Violation
Blog on blog.domain.com instead of domain.com/blog
Consequence
Blog link equity doesn't flow to main domain; separate crawl budget
Violation
Shop on shop.domain.com instead of domain.com/shop
Consequence
Product pages don't benefit from domain authority; diluted signals
Violation
Migrating subdirectory to subdomain without redirects
Consequence
Loss of indexed pages, link equity, and rankings for migrated content
05 The Fix
Migrate subdomain content to subdirectories where SEO value sharing is desired. Implement 301 redirects for all moved URLs. Monitor Search Console for coverage changes during migration.