danny-avila/LibreChat · error · Error

Unsupported file type

Error message

Unsupported file type

What it means

filterFile() throws this at process.js:1365 when fileConfig.checkType returns false for the uploaded file's mimetype against endpointFileConfig.supportedMimeTypes. The supported list is derived from librechat.yaml fileConfig.supportedMimeTypes (per-endpoint) or the framework default. It is the MIME gate that runs after the size check.

Source

Thrown at api/server/services/Files/process.js:1365

  });
  const fileSizeLimit =
    isAvatar === true ? fileConfig.avatarSizeLimit : endpointFileConfig.fileSizeLimit;

  if (file.size > fileSizeLimit) {
    throw new Error(
      `File size limit of ${fileSizeLimit / megabyte} MB exceeded for ${
        isAvatar ? 'avatar upload' : `${endpoint} endpoint`
      }`,
    );
  }

  const isSupportedMimeType = fileConfig.checkType(
    file.mimetype,
    endpointFileConfig.supportedMimeTypes,
  );

  if (!isSupportedMimeType) {
    throw new Error('Unsupported file type');
  }

  if (!image || isAvatar === true) {
    return;
  }

  if (!width) {
    throw new Error('No width provided');
  }

  if (!height) {
    throw new Error('No height provided');
  }
}

module.exports = {
  filterFile,
  processFileURL,

View on GitHub (pinned to 5ff282f900)

Solutions

1. Convert the file to a supported type (e.g. PNG/JPEG for images) before uploading.
2. Add the required mimetype to fileConfig.supportedMimeTypes in librechat.yaml for that endpoint.
3. Ensure the uploaded file extension matches its real content so multer infers the correct mimetype.

Example fix

// librechat.yaml before
fileConfig:
  supportedMimeTypes:
    - image/jpeg
    - image/png
// after
fileConfig:
  supportedMimeTypes:
    - image/jpeg
    - image/png
    - image/webp

function isSupportedMime(file, supported) {
  return supported.includes(file.type);
}

const hasSupportedMime = (file, supported) => supported.includes(file?.type);

When it happens

Trigger: Uploading a file whose Content-Type / detected mimetype is not in the endpoint's supportedMimeTypes list, e.g. a .heic image on an endpoint that only allows image/jpeg, image/png. A .docx on a code-only endpoint. The check uses the multer-reported mimetype, which is inferred from extension/headers.

Common situations: User uploads a modern format (avif, webp, heic) not in the default list. A misnamed extension causes multer to infer the wrong mimetype. An admin tightened supportedMimeTypes and users still send legacy formats.

Related errors

• No endpoint provided
• File size limit of ${fileSizeLimit / megabyte} MB exceeded f
• No file_id provided
• Empty file uploaded
• No width provided

AI-assisted analysis of danny-avila/LibreChat@5ff282f900 (2026-08-12). Data as JSON: /api/errors/3b33747eb8e35c4e. Report an issue: GitHub.