URL Slugs and SEO: Best Practices for Developers

What is a URL Slug?

A URL slug is the human-readable, SEO-friendly part of a URL that identifies a page:

https://blog.example.com/posts/how-to-format-json-like-a-pro
                                ↑
                          This is the slug

Good slugs are short, descriptive, lowercase, and use hyphens as separators. They're a direct ranking signal in SEO and significantly affect click-through rates from search results.

Slug Generation Rules

The algorithm for converting a title to a slug:

function generateSlug(title) {
  return title
    .normalize('NFD')                    // Decompose unicode characters
    .replace(/[\u0300-\u036f]/g, '')   // Remove diacritics (é → e)
    .toLowerCase()                        // Lowercase everything
    .replace(/[^a-z0-9\s-]/g, '')      // Remove non-alphanumeric
    .trim()                               // Remove edge whitespace
    .replace(/[\s]+/g, '-')             // Replace spaces with hyphens
    .replace(/[-]+/g, '-')               // Collapse multiple hyphens
    .replace(/^-|-$/g, '');              // Remove leading/trailing hyphens
}

generateSlug('Hello, World! How are you?');
// → 'hello-world-how-are-you'

generateSlug('Héllo Wörld — Ünïcode');
// → 'hello-world-unicode'

Handling Unicode and International Characters

The normalize('NFD') step is critical for international content:

// NFD decomposes accented characters into base + combining marks
'café'.normalize('NFD')  // 'cafe\u0301' (e + combining accent)
// Then remove combining marks → 'cafe'

// Vietnamese example
'Nguyễn Thị Hương'.normalize('NFD').replace(/[\u0300-\u036f]/g, '')
// → 'Nguyen Thi Huong'

Stop Words: Include or Exclude?

Stop words are common words that add little value to SEO: a, an, the, and, or, in, on, at, to, for...

For blog posts and articles: Removing stop words creates shorter, more focused slugs:

Title: "A Beginner's Guide to Regular Expressions"
With stops:    a-beginners-guide-to-regular-expressions
Without stops: beginners-guide-regular-expressions

For product names, proper nouns, or short titles: Keep stop words. Removing them from "The Dark Knight" produces "dark-knight" which loses SEO context.

Recommendation: Remove stop words only for long editorial titles (6+ words). Preserve them for names and brands.

Maximum Slug Length

There's no hard limit in HTTP, but practical limits apply:

• 50–60 characters: Sweet spot for readability and SEO
• 100 characters: The upper reasonable limit
• 2048 characters: URL limit in most browsers (relevant for query strings, not slugs)

When truncating, always cut at a word boundary:

function truncateSlug(slug, maxLength = 60) {
  if (slug.length <= maxLength) return slug;
  const truncated = slug.slice(0, maxLength);
  return truncated.slice(0, truncated.lastIndexOf('-'));
}

truncateSlug('how-to-write-clean-maintainable-javascript-code-that-scales', 50);
// → 'how-to-write-clean-maintainable-javascript-code'

Handling Duplicates

When two posts have the same title, you need a disambiguation strategy:

// Option 1: Append a counter
async function uniqueSlug(base) {
  let slug = base;
  let counter = 1;
  while (await slugExists(slug)) {
    slug = `${base}-${counter++}`;
  }
  return slug;
}
// 'javascript-tips', 'javascript-tips-2', 'javascript-tips-3'

// Option 2: Append a short ID (better for high-volume systems)
import { nanoid } from 'nanoid';
const slug = `${base}-${nanoid(6)}`;
// 'javascript-tips-a3f9kz'

SEO Best Practices

1. Include the primary keyword early in the slug:

Good: /typescript-discriminated-unions
Bad:  /a-guide-to-using-discriminated-unions-in-typescript

2. Don't change slugs once indexed. If you must change a slug, set up a 301 permanent redirect from the old URL to the new one.

3. Avoid dates in slugs (unless the date is the point, like /2025/01/15/...). Dates make content feel stale and require a redirect when you update the article.

4. Use hyphens, not underscores. Google treats hyphens as word separators but underscores as connectors. my-post = two words; my_post = one word.

5. Keep slugs consistent in depth:

/blog/post-title       ← Good (flat structure)
/blog/category/post    ← Also fine (nested, but consistent)
/b/c/d/post-title      ← Bad (too deep, dilutes link equity)

Testing and Generating Slugs

Use HeoLab's Slug Generator to instantly convert titles to slugs with options for separator type, stop word removal, lowercase, and character limits. It also generates kebab-case, snake_case, dot.case, and camelCase variants at once.

Conclusion

The perfect slug is short, lowercase, hyphen-separated, keyword-rich, and free of special characters. Get the algorithm right once (or use a trusted library like slugify) and your URLs will serve both users and search engines well for years.