The term "slug" in the context of web publishing has a surprisingly old-media origin. In newspaper and wire service jargon, a slug was a short label assigned to a story during production—a concise identifier that editorial staff used to reference an article as it moved through the publishing pipeline. When content management systems for the web emerged in the early 2000s, they borrowed the term to describe the URL-friendly identifier generated from an article's title. WordPress, one of the earliest and most influential blogging platforms, popularized the concept by automatically generating slugs from post titles, and the term became standard vocabulary across the web development community.

The technical process of slug generation involves several text transformation steps. First, the text is converted to lowercase, since URLs are case-insensitive by convention and search engines may treat differently-cased URLs as separate pages. Next, accented and non-Latin characters are transliterated to their closest ASCII equivalents—é becomes e, ü becomes u, ñ becomes n. This transliteration step is crucial for internationalization, as it allows content in any language to have ASCII-safe URLs while preserving semantic meaning. Characters that have no reasonable ASCII equivalent are typically removed entirely.

Spaces and punctuation are then converted to separator characters, typically hyphens. The choice between hyphens and underscores has SEO implications that Google's Matt Cutts clarified in a widely-referenced 2011 statement: Google treats hyphens as word separators but treats underscores as word joiners. This means "best-coffee-shops" is indexed as three separate words, while "best_coffee_shops" might be treated as a single compound token. This distinction is why virtually all modern CMS platforms and SEO guides recommend hyphens as the default separator.

Stopword removal is a more nuanced decision in slug generation. Stopwords are common function words like "the," "a," "in," "of," and "and" that carry little semantic meaning. Removing them produces shorter, cleaner URLs ("best-coffee-shops-portland" vs. "the-best-coffee-shops-in-portland"), which some SEO practitioners prefer. However, others argue that preserving stopwords creates more natural, readable URLs that better match search queries. Most slug generators make this configurable, allowing content creators to choose based on their SEO strategy and style preferences.

URL length is another practical consideration. While the HTTP specification does not define a maximum URL length, browsers and servers impose practical limits. Internet Explorer historically limited URLs to 2,083 characters, and most SEO experts recommend keeping the entire URL under 75–100 characters for optimal search engine treatment. Slug generators often include a maximum length option that truncates the slug at a word boundary, preventing awkward mid-word cuts while keeping URLs concise.

The concept of permanent URLs (permalinks) adds importance to slug generation. Once a URL is published and indexed by search engines, linked from other sites, or bookmarked by users, changing it results in broken links and lost SEO value. This makes the initial slug generation decision consequential—a well-crafted slug should remain relevant and descriptive for the lifetime of the content, which in the case of many web pages can be years or even decades.