File Acceptance On Upload

You can limit both the file types and the file size accepted by your uploader
How to configure - File Type

When creating the simple-file-upload input component, add a data attribute of accepted.

You can use data-accepted=image/* to allow only image files.
You can use any valid filename extension, starting with a period (".") character. For example: .jpg, .pdf, or .doc.

You can also provide a list of file types if you'd like to allow more than one.

Examples

Allow only jpegs

<input class="simple-file-upload" data-accepted="image/jpeg"
type="hidden" name="user[avatar_url]" id="user_avatar_url">

Allow all image types

<input class="simple-file-upload" data-accepted="image/*" type="hidden" name="user[avatar_url]" id="user_avatar_url">

Allow only pdf files

<input class="simple-file-upload" data-accepted=".pdf" type="hidden" name="user[avatar_url]" id="user_avatar_url">

Allow images and pdf files

 <input class="simple-file-upload" data-tag="website-files" type="hidden" name="user[icon_url]" 
 id="user_icon_url" data-accepted ="image/*, .pdf">
How to configure - File Size

When creating the simple-file-upload input component, add a data attribute of maxFileSize.

You can use data-maxFileSize=3 to limit uploaded file size to 3 MB for example.
The maxFileSize cannot exceed the file size for your plan.

Example

Limit uploaded files to 3MB.

<input class="simple-file-upload" data-maxFileSize="3"
type="hidden" name="user[avatar_url]" id="user_avatar_url">
Ruby on Rails Form Helpers

If you're using Ruby on Rails form helpers, the data attributes are specified like this:

<%= f.hidden_field :avatar_url, class: "simple-file-upload", data: { accepted: "image/*", maxFileSize: "3"} %>