WordPress provides a comprehensive URL generation system that handles permalinks, site URLs, admin URLs, and canonical URL management. The system is flexible, supporting both "pretty permalinks" and query-string-based URLs.

Core Concepts

URL Types

WordPress distinguishes between several URL types:

Permalink Structure

Permalinks are the permanent URLs to posts, pages, and archives. WordPress supports:

• Plain: ?p=123
• Day and name: /2024/02/09/sample-post/
• Month and name: /2024/02/sample-post/
• Numeric: /archives/123
• Post name: /sample-post/
• Custom structure: Using rewrite tags like %postname%, %category%, %author%

URL Scheme Handling

The set_url_scheme() function normalizes URLs to use the correct protocol:

// Forces HTTPS
set_url_scheme( $url, 'https' );

// Uses current scheme (respects is_ssl())
set_url_scheme( $url );

// Relative URL (strips protocol and host)
set_url_scheme( $url, 'relative' );

Primary Source Files

URL Generation Architecture

Post Permalinks

get_permalink( $post )
    ├── get_page_link()      → For pages
    ├── get_attachment_link() → For attachments  
    └── get_post_permalink() → For custom post types

Archive Permalinks

Archive URLs
    ├── get_year_link()          → /2024/
    ├── get_month_link()         → /2024/02/
    ├── get_day_link()           → /2024/02/09/
    ├── get_term_link()          → /category/news/
    ├── get_author_posts_url()   → /author/admin/
    └── get_post_type_archive_link() → /books/

Feed URLs

Feed URLs
    ├── get_feed_link()               → Main site feed
    ├── get_post_comments_feed_link() → Post comments feed
    ├── get_author_feed_link()        → Author posts feed
    ├── get_category_feed_link()      → Category feed
    └── get_tag_feed_link()           → Tag feed

Canonical URLs

Canonical URLs prevent duplicate content issues by redirecting to the "correct" URL version:

How redirect_canonical() Works

1. Builds requested URL from $_SERVER variables
2. Determines correct URL based on query type (single, archive, etc.)
3. Handles edge cases:
   • www vs non-www normalization
   • Trailing slash consistency
   • Query parameter cleanup
   • Pagination handling
4. Issues 301 redirect if URLs differ

SEO Implications

• www vs non-www normalization
• Trailing slash consistency
• Query parameter cleanup
• Pagination handling

Legacy Bookmarks (Links Manager)

The Bookmarks API manages external links (formerly "blogroll"). Disabled by default since WordPress 3.5 but still functional.

Link Data Structure

object(stdClass) {
    link_id          // Unique ID
    link_url         // The URL
    link_name        // Display name
    link_image       // Optional image URL
    link_target      // _blank, _top, or empty
    link_description // Description text
    link_visible     // Y or N
    link_owner       // User ID who created
    link_rating      // 0-10 rating
    link_updated     // Last update timestamp
    link_rel         // Relationship (XFN)
    link_notes       // Private notes
    link_rss         // RSS feed URL
    link_category    // Array of category IDs
}

Trailing Slashes

WordPress handles trailing slashes via user_trailingslashit():

// Adds or removes trailing slash based on permalink settings
$url = user_trailingslashit( $url, 'single' );

The $type_of_url parameter allows different handling for:

• www vs non-www normalization
• Trailing slash consistency
• Query parameter cleanup
• Pagination handling

Multisite URL Functions

For multisite installations:

Shortlinks

WordPress provides a shortlink system for sharing:

// Get shortlink for current post
$shortlink = wp_get_shortlink();

// Default format: ?p=123
// Can be filtered for custom shorteners

The shortlink is:

• Consolidates link equity to canonical URL
• Prevents penalty for duplicate content
• Normalizes URL variations

Common Patterns

Getting the Current Page URL

// For posts/pages
$url = get_permalink();

// For archives
$url = get_term_link( $term );

// For search results
$url = get_search_link( $query );

Building Admin URLs

// Edit post screen
$url = get_edit_post_link( $post_id );

// Custom admin page
$url = admin_url( 'admin.php?page=my-plugin' );

// User profile
$url = get_edit_user_link( $user_id );

Navigation Links

// Previous/Next post
$prev = get_previous_post_link();
$next = get_next_post_link();

// Pagination
$links = paginate_links( $args );

Best Practices

1. Use URL functions instead of hardcoding paths
2. Escape URLs with esc_url() before output
3. Respect permalink structure – use built-in functions
4. Use relative URLs when appropriate for portability
5. Filter URLs only when necessary; prefer built-in hooks