Client-Side Validation

All validation runs in the browser before upload begins. Users see immediate feedback without waiting for a server response.

What you should see: rejections happen the instant you choose a file, with no network request. The rules are .jpg/.png/.gif/.pdf, 1 KB–5 MB, at most 5 files — try a 6th file or a .txt to see each rule fire.

Drag & drop files here, or paste from clipboard

Try uploading a file that violates one of the rules: wrong extension, too large, too small, or more than 5 files.

<core-upload asp-upload-url="/api/upload/upload"
 asp-extensions=".jpg,.png,.gif,.pdf"
 asp-max-size="5MB"
 asp-min-size="1KB"
 asp-max-count="5"
 asp-multiple="true"
 asp-progress="true">
</core-upload>