URL Slugs: Best Practices for SEO-Friendly URLs

What Is a URL Slug?

A slug is the URL-friendly identifier that appears after the last slash in a page URL:

https://example.com/blog/how-to-generate-url-slugs
                          ↑ this is the slug

A good slug describes the content concisely, contains relevant keywords, uses only lowercase letters, digits, and hyphens, and avoids stop words.

SEO Rules for Slugs

Use hyphens, not underscores. Google treats hyphens as word separators; underscores join words into one. url-slug = two words, url_slug = one word "url_slug".
Lowercase only. URLs are technically case-sensitive; mixing case creates duplicate content risk.
Include the target keyword. The primary keyword in the slug is a light ranking signal.
Keep it short. Aim for 3–5 words. Long slugs get truncated in search results and shared links.
Remove stop words (a, an, the, and, or, but) unless they are part of the keyword phrase.
Never change published slugs without a 301 redirect — broken URLs kill backlink equity and index coverage.

Generating Slugs in JavaScript

function slugify(str) {
  return str
    .toLowerCase()
    .normalize("NFD")               // decompose accented chars: é → e + ́
    .replace(/[\u0300-\u036f]/g, "") // strip diacritics
    .replace(/[^a-z0-9\s-]/g, "")  // remove non-alphanumeric
    .trim()
    .replace(/\s+/g, "-")           // spaces to hyphens
    .replace(/-+/g, "-");           // collapse multiple hyphens
}

slugify("Hello, World! This is a Test.");
// "hello-world-this-is-a-test"

slugify("Héllo Wörld");
// "hello-world"

Generating Slugs in Python

import re
import unicodedata

def slugify(text):
    text = unicodedata.normalize("NFD", text.lower())
    text = "".join(c for c in text if unicodedata.category(c) != "Mn")
    text = re.sub(r"[^a-z0-9\s-]", "", text)
    text = re.sub(r"[\s-]+", "-", text).strip("-")
    return text

# Or use the python-slugify library:
from slugify import slugify
slugify("Hello, World!")  # "hello-world"

Handling Unicode and International Characters

// Transliterate non-ASCII to ASCII equivalents
// Using the 'slugify' npm package
import slugify from "slugify";

slugify("Ärger mit Übergepäck", { locale: "de" });
// "aergermit-ueberpaeaeck"  ← German umlaut expansion

slugify("北京", { locale: "zh" });
// Requires manual transliteration or a library like pinyin

Unique Slugs in a Database

// When title-based slug already exists, append a number
async function uniqueSlug(title, db) {
  const base = slugify(title);
  let slug = base;
  let i = 2;
  while (await db.exists({ slug })) {
    slug = `${base}-${i++}`;
  }
  return slug;
}

Generate Slugs Instantly

Use ToolsVito's Slugify tool to convert any text to a URL-friendly slug with configurable separators and Unicode transliteration.