The Short Answer on Hyphens

Yes, hyphens are the recommended way to separate words in URLs. Search engines interpret a hyphen as a word boundary, which means a slug written with hyphens is read as distinct words rather than one long string. Underscores were historically treated as word joiners rather than separators, so a slug using them was more likely to be interpreted as a single token. Modern parsing is far more forgiving and plenty of underscore URLs rank perfectly well, but the guidance has never changed: use hyphens for new URLs and you remove all ambiguity.

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Why Word Separation Matters at All

URLs are one of the signals search engines use to understand a page before they process its content, and they are one of the first things users see in a search result. A slug that reads as clear words communicates the topic instantly. A slug that reads as an unbroken string forces both machines and people to guess. The effect on rankings is modest, because content and links dominate, but the effect on comprehension and click behaviour is real and free to capture.

There is also a sharing dimension. Readable URLs get copied into messages, documents and social posts more confidently than cryptic ones, and a URL that describes its destination reduces hesitation before a click.

Hyphens Versus Underscores Versus Nothing

A hyphenated slug separates words cleanly and is the industry standard. An underscored slug is valid and generally understood today, but it remains the less clear option and looks dated. A slug with no separator at all is the worst choice, because a long concatenated string is genuinely difficult to parse and can produce accidental misreadings that embarrass a brand.

Spaces should never appear in a slug. A space becomes a percent-encoded sequence, turning a clean address into visual noise that breaks in emails and copy-paste workflows. Plus signs are also poor choices because they can be interpreted as encoded spaces in query strings, creating subtle bugs.

Should You Rewrite Existing Underscore URLs?

Usually no. Changing URLs requires redirects, internal link updates, sitemap regeneration and a period of ranking volatility while search engines reprocess the changes. The marginal gain from swapping underscores for hyphens rarely justifies that risk on an established site with healthy traffic.

The calculation changes if you are already migrating for another reason, if the affected pages have little traffic or authority, or if the current URLs are genuinely broken in other ways such as containing session identifiers, dates that are no longer accurate or long parameter strings. In those cases, fix everything at once with a complete one-to-one redirect map.

Building a Good Slug

Keep slugs short and descriptive. Include the primary topic words and drop everything else. Remove filler words such as articles and prepositions where they add no meaning, but do not strip so aggressively that the phrase becomes awkward. Use lowercase exclusively, because many servers treat paths as case sensitive and mixed casing invites duplicate URLs.

Avoid stuffing keywords. Repeating a term across a slug looks manipulative and provides no benefit. Avoid dates unless the content is genuinely time-bound, because a date in a URL makes evergreen content look stale and prevents you from updating it cleanly. Avoid stop-word soup, deep unnecessary nesting and category prefixes that will change when your taxonomy evolves.

URL Depth and Structure Beyond Separators

Separators are only part of the picture. Shallow, logical paths help both users and crawlers understand hierarchy. A page reachable at a two-level path signals importance more clearly than the same page buried five levels deep. Group related content under meaningful sections, but resist creating folders for their own sake, since every additional level is another thing to maintain and another opportunity for inconsistency.

Be consistent across templates. If blog posts sit at one pattern and service pages at another, document the rules so future pages match. Inconsistent patterns accumulate into technical debt that becomes painful to unwind.

Trailing Slashes, Casing and Duplicate Variants

Many duplicate-URL problems have nothing to do with hyphens. A page reachable with and without a trailing slash, with and without www, over http and https, and in multiple casings can produce several indexable variants of identical content. Choose one canonical form for each dimension, redirect the alternatives permanently, and make internal links point at the canonical version directly rather than relying on redirects.

Non-English and Special Characters

For multilingual sites, transliteration is usually preferable to encoded non-ASCII characters, because encoded slugs render as long percent sequences that are unreadable when shared. Some markets genuinely benefit from native-script URLs where the audience expects them, so weigh readability for your specific users against the cosmetic cost. Whatever you choose, apply it consistently and ensure your CMS generates slugs predictably rather than producing different results depending on who publishes the page.

Practical Slug Checklist

Use lowercase letters, numbers and hyphens only. Separate every word with a single hyphen. Keep slugs under roughly five words where possible. Include the main topic term once. Exclude dates, session identifiers and tracking parameters. Choose one trailing-slash convention and enforce it. Redirect all legacy variants permanently. Update internal links to final URLs. Document the pattern for your team so new pages follow it automatically.

Conclusion

Hyphens are the correct separator for URLs, and they always have been. They mark word boundaries clearly, produce readable addresses and eliminate any parsing ambiguity. Underscores are survivable but outdated, and concatenated words or encoded spaces are genuinely harmful to readability. Set a clean lowercase hyphenated convention, apply it consistently, and spend your remaining effort on the content and links that actually decide rankings.