Accepting specific file types

By providing the accept prop you can make the dropzone accept specific file types and reject the others. The value is an object keyed by MIME type with an array of file extensions as values.

Pairing a wildcard MIME type with extensions narrows it down to those extensions - {"image/*": [".jpeg", ".png"]} accepts only .jpeg and .png files, not every image type. Use an empty array ({"image/*": []}) to accept all files of that type.

function Accept() {
  const {acceptedFiles, fileRejections, getRootProps, getInputProps} = useDropzone({
    accept: {"image/jpeg": [], "image/png": []}
  });
 
  const acceptedFileItems = acceptedFiles.map(file => (
    <li key={file.path}>
      {file.path} - {file.size} bytes
    </li>
  ));
 
  const fileRejectionItems = fileRejections.map(({file, errors}) => (
    <li key={file.path}>
      {file.path} - {file.size} bytes
      <ul>
        {errors.map(e => (
          <li key={e.code}>{e.message}</li>
        ))}
      </ul>
    </li>
  ));
 
  return (
    <section className="container">
      <div {...getRootProps({className: "dropzone"})}>
        <input {...getInputProps()} />
        <p>Drag 'n' drop some files here, or click to select files</p>
        <em>(Only *.jpeg and *.png images will be accepted)</em>
      </div>
      <aside>
        <h4>Accepted files</h4>
        <ul>{acceptedFileItems}</ul>
        <h4>Rejected files</h4>
        <ul>{fileRejectionItems}</ul>
      </aside>
    </section>
  );
}

Reacting during the drag

Because of HTML5 File API limitations, file names/extensions aren't readable during a drag, so use MIME types (e.g. image/*) if you want to react with isDragAccept / isDragReject:

const {isDragActive, isDragAccept, isDragReject, getRootProps, getInputProps} = useDropzone({
  accept: {"image/*": [".jpeg", ".png"]}
});

Mime type determination is not reliable across platforms. CSV files, for example, are reported as text/plain under macOS but as application/vnd.ms-excel under Windows.

isDragUnknown and custom validators

Your custom validator is typed (file: File) => … and usually reads file.name, file.size, etc. During a drag those aren't available (the browser only exposes a MIME type), so react-dropzone doesn't run the validator until drop. While a validator is configured and the built-in checks pass, the drag state is neither accept nor reject but isDragUnknown — the outcome can only be confirmed once the real files are dropped:

const {isDragAccept, isDragReject, isDragUnknown, getRootProps, getInputProps} = useDropzone({
  validator: myValidator
});
 
// isDragUnknown === true  → "these files might be rejected on drop"

A file whose MIME type is confidently wrong (or a selection that breaks multiple/maxFiles) is still isDragReject during the drag, even with a validator — a validator can only ever add rejections on drop, never rescue one.

Restoring the full MIME-type table

react-dropzone resolves each file's MIME type through file-selector's fromEvent — the default for the getFilesFromEvent prop — which infers the type from the file extension when the browser leaves a file typeless (common with drag 'n' drop and File System Access sources).

As of file-selector v4, only a small built-in set of common extensions is bundled, so the core stays lightweight. Because accept matches by file extension as well as MIME type, most configurations keep working regardless. You only need the full table when matching purely by MIME type (e.g. image/*) against typeless sources — pass the full COMMON_MIME_TYPES table via getFilesFromEvent (add file-selector to your dependencies to import from it):

npm install file-selector

import {useDropzone} from "react-dropzone";
import {fromEvent} from "file-selector";
import {COMMON_MIME_TYPES} from "file-selector/mime";
 
function FullMimeCoverage() {
  const {getRootProps, getInputProps} = useDropzone({
    getFilesFromEvent: event => fromEvent(event, {mimeTypes: COMMON_MIME_TYPES})
  });
  // ...
}