Google Hyphens vs Underscores URLs SEO Guidance: A Technical Comparison for Regulated Industries
Hyphens are the documented standard for word separation in URLs. Google systems are specifically engineered to treat hyphens as spaces, whereas underscores are often treated as word joiners, potentially merging keywords into a single, unrecognizable string.
Best for: Hyphens are best for all public-facing content slugs, especially in YMYL (Your Money Your Life) industries where keyword clarity is essential for both users and crawlers.
Best for: Underscores are generally reserved for technical parameters, programming variables, or internal tracking strings where word separation is not an SEO requirement.
Hyphens (The Standard Separator) vs Underscores (The Connector)
Feature-by-Feature Comparison
0 wins for Hyphens (The Standard Separator) · 0 wins for Underscores (The Connector) · 4 ties
Strengths & Weaknesses
✓ Pros
- Explicitly recommended by Google Search Central documentation
- Treated as a space by search engine parsing algorithms
- Highly readable for users in SERP snippets and address bars
- Default setting for nearly all SEO-focused content management systems
- Reduces the risk of keyword merging in the search index
- Maintains clarity even when the URL is underlined in a document
✗ Cons
- Can lead to longer URLs if overused in deep folder structures
- Requires consistent implementation across the entire site architecture
- Manual entry on mobile devices can be slightly slower than alphanumeric characters
Best For
✓ Pros
- Standard convention for many programming languages and database schemas
- Prevents word wrapping in some very specific legacy terminal environments
- Useful for separating technical parameters from descriptive slugs
- Allows for clear distinction between SEO keywords and tracking IDs
- Technically a valid character in the URI specification
✗ Cons
- Not recognized by Google as a standard word separator for indexing
- Can be hidden by underlines in browser interfaces and documents
- Increases the likelihood of keyword concatenation issues
- Contradicts official SEO best practices and documentation
Best For
Frequently Asked Questions
Yes, Google's core recommendation has not changed. While their algorithms have become significantly more sophisticated at understanding natural language and context, the hyphen remains the explicit signal for a word separator in a URL. In my practice, I have observed that adhering to this standard reduces the risk of indexing errors.
When you use hyphens, you are following a documented process that Google has supported for over a decade. This consistency is vital for maintaining visibility in competitive, regulated markets where every technical detail contributes to the overall authority of the entity.
Using underscores is unlikely to cause a manual penalty or a total loss of rankings, but it can lead to suboptimal performance. The primary risk is that Google might not correctly identify the individual keywords within your URL. If your URL is 'best_tax_attorney', there is a small but measurable risk that it won't be as strongly associated with the search term 'best tax attorney' as a hyphenated version would be.
In the context of compounding authority, you want to eliminate these small technical hurdles. We prefer to use hyphens to ensure the system is as efficient as possible.
This depends on the existing authority of the pages. If the pages are already ranking well and have significant backlink profiles, the risk of a temporary dip during the redirect process might outweigh the benefits of the change. However, for new content or pages that are underperforming, migrating to a hyphenated structure as part of a broader technical audit is often advisable.
What I've found is that a clean, consistent URL structure is easier to manage and scale over time. If you do make the change, you must use 301 redirects to ensure no equity is lost.
AI search models and Large Language Models (LLMs) rely on tokenization to understand text. Hyphens are a clear signal to these models that the words are separate tokens. When an AI assistant like Google's SGE or an LLM like GPT-4 parses a URL to cite a source, the clarity provided by hyphens helps it accurately attribute the content to the correct keywords.
In a reviewable visibility framework, we ensure that every element of the page, including the URL, is optimized for these new search environments. Hyphens provide a cleaner, more reliable signal for these AI systems.
Underscores are better only in non SEO contexts. For example, if you are a developer managing internal API endpoints or database queries where the URL is never intended to be indexed by a search engine, underscores are a standard and acceptable choice. They are also useful in URL parameters for tracking, such as 'utm_source' or 'campaign_id'.
In these cases, the underscore helps distinguish the technical data from the content slug. For any part of the URL that you want a human to read or a search engine to index, hyphens are the superior choice.
Hyphens themselves do not significantly impact URL length more than underscores would, as both are single characters. However, the goal should always be to keep URLs concise and descriptive. In my experience, a URL that is too long can be truncated in search results, which reduces the click through rate.
Whether you use hyphens or underscores, the focus should be on including the most important keywords and removing unnecessary filler words. A hyphenated URL that is structured around a clear hierarchy is the most effective way to communicate the page's topic to both users and crawlers.