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FAQ • Support

Why WordPress Won’t Let You Upload Certain Files

Field Note #147
🔬 Generalized 🟢 Beginner ⏱ 5 Minutes ✓ Observation from Experience
You try to upload a file through Media → Add New — maybe a .js file, or some other less common file type — and WordPress stops you cold: “Sorry, you are not allowed to upload this file type.” You’re the site’s own administrator. Surely you’re allowed to upload whatever you want?
Not by default, and it has nothing to do with your account or your hosting plan specifically.

What’s actually happening
WordPress maintains a built-in list of file types it will accept through the Media Library, for security reasons — this applies to every account on every WordPress site, admin included. It’s not a permissions setting you’ve missed, and it’s not something your hosting provider did to you. A handful of file types, script files especially, simply aren’t on that default list, regardless of who’s uploading them or why.How to tell the difference
This one doesn’t require much detective work — the error message says exactly what’s happening. If you see “you are not allowed to upload this file type,” you’ve found the cause; there’s no deeper mystery to chase.

The fix
A developer can add a small snippet of code using WordPress’s built-in upload_mimes filter, which explicitly allows specific file extensions through the Media Library uploader. This is a standard, well-documented WordPress customization, not a workaround.
One thing worth knowing: on some hosting environments, this filter alone may not fully resolve it — certain hosts layer additional restrictions on top of WordPress’s own defaults. If the filter doesn’t clear it, uploading the file directly through your hosting account’s File Manager (found in cPanel or your host’s equivalent control panel) is a reliable fallback — it uploads at the raw server level, bypassing WordPress’s own upload system entirely.

How to avoid it next time
If you know ahead of time that a project will require uploading an uncommon file type, mention it to your developer before you actually need it, so the allowlist can be adjusted in advance — or plan from the start to use File Manager for that specific file, sidestepping the restriction altogether.

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