Sveltia CMS: Default slug generation is not URL-safe (can break static site builds)

[RDjarbeng]

I ran into a frustrating build failure on my static site that turned out to be caused by how Sveltia CMS generates slugs by default.

If a post title contains certain characters (e.g., ellipsis …, em dashes —, non-ASCII quotes, etc.), Sveltia keeps the original Unicode characters in the filename. Many static site generators (and GitHub Pages in particular) don’t handle these characters well in file paths, which can result in broken builds or missing pages.

Example of a problematic filename I got:
my-post-title…-with-ellipsis.md

I had to manually rename the file and push a fix:

Solution

The solution is to force ASCII-only, URL-friendly slugs in config.yml:

slug:
  encoding: 'ascii'           # Convert Unicode → closest ASCII equivalent
  clean_accents: true          # Strip accents (é → e, etc.)
  sanitize_replacement: '-'   # Replace any remaining invalid chars with a hyphen

Without these settings, special characters in titles can silently break your site during deployment—especially on GitHub Pages or other environments that are strict about filesystem-safe filenames.

Posting this here in case anyone else is pulling their hair out over mysterious build failures. Highly recommend adding the above slug configuration if you’re using Sveltia CMS with any static site generator.

Hope this helps someone! 🚀

[kyoshino]

For backward compatibility with Netlify/Decap CMS, we are not going to change the default. Also, not everyone is using GitHub Pages (Jekyll) or writing in English.

[kyoshino]

We could mention it on the troubleshooting page in the upcoming docs site.

[kyoshino]

Not sure if the issue is rather Jekyll-specific. Searching the net finds:

• https://stackoverflow.com/questions/60156042/local-jekyll-cannot-load-unicode-urls
• https://stackoverflow.com/questions/41941320/jekyll-encoding-name-of-category-special-characters
• https://jekyllrb.com/docs/liquid/filters/#options-for-the-slugify-filter

[RDjarbeng]

Could be. I'm not sure how other frameworks handle non-ascii characters like periods in file names though.