Understanding the Use of IDs and Slugs in Website URLs: A Deep Dive

When browsing websites, particularly those related to media content such as anime, manga, or other cataloged resources, you might notice a common URL pattern: a unique identifier (ID) coupled with a descriptive slug (often the title or a variation thereof). For example:

• https://anilist.co/manga/53390/Attack-on-Titan/
• https://myanimelist.net/anime/16498/Shingeki_no_Kyojin

These URLs follow a structure such as <domain>/<route>/<resourceId>/<slug>, where the resource ID is a numerically immutable value, and the slug is a human-readable, descriptive component. This design raises important questions: Why include both an ID and a slug? Why not rely solely on the immutable ID for resource identification? What’s the benefit of maintaining a mutable slug that often describes the resource’s title?

The Rationale Behind Combining IDs with Slugs

1. Ensuring Unique and Reliable Resource Identification
   The core reason for including an immutable ID in the URL is to guarantee unambiguous resource identification. Numerically unique IDs (e.g., 53390) are constant identifiers assigned at the database level. They provide a reliable reference point that does not change over time or due to content modifications. Relying solely on slugs can be problematic because titles or descriptions may change — for instance, if a show is renamed or rebranded.

2. Enhancing User Experience and SEO with Descriptive URLs
   Adding a slug that mirrors the resource’s title improves readability for users and can boost SEO performance. Search engines favor descriptive URLs that include keywords relevant to the page’s content. A URL like /manga/53390/Attack-on-Titan/ immediately communicates the content to both users and search engines, which can enhance click-through rates and ranking relevance.

3. Maintaining URL Stability Amid Content Updates
   While slugs are generally meant to be “mutable,” best practices involve preserving URL structures even if the resource’s title changes. That is, the primary identifier remains the ID, which remains constant, ensuring older links and bookmarks continue to