May 12, 2026

Fix Astro 'Duplicate id found' content warning

If you see a warning like this during build:

[glob-loader] Duplicate id \"your-post-slug\" found in ...

you are usually dealing with one of two issues:

duplicate files/slugs in src/content/blog
stale generated content cache after renames or rapid edits

Here is the fastest way to fix it reliably.

Step 1: verify there is only one file per slug

Check your blog content directory for lookalike filenames:

ls -la src/content/blog

Things to watch for:

same slug in .md and .mdx
accidental copy like post copy.md
case-only differences (Post.md vs post.md)

Step 2: clear Astro content cache

When files were renamed/moved, stale cache is common.

rm -rf .astro
npm run build

If the warning disappears, cache was the issue.

Step 3: restart a single dev server

Multiple astro dev instances on different ports can make warnings seem random.

pkill -f "astro dev" || true
pkill -f "npm run dev" || true
npm run dev

Step 4: keep slug generation simple

Use one post per file and keep filenames unique and lowercase:

fix-worker-env-vars.md
astro-contact-form-turnstile.md

Avoid spaces and punctuation-heavy names.

Why this works

Astro content IDs are derived from content file paths/slugs. Duplicate sources or stale cache state causes collisions. Cleaning files + cache removes both failure modes.

If this warning appears in CI only, add a clean build step in CI (remove .astro before build) to match local behavior.