# EPUBCheck OPF-093: The media-type attribute is required…

Source: https://epublab.com/epubcheck/opf-093/ (updated 2026-11-03)

EPUBCheck OPF-093 is an error message: “The "media-type" attribute is required for linked resources located in the EPUB container.” A link element in the metadata points to a file inside the EPUB but has no media-type attribute.

- Official message (EPUBCheck 5.4.0): The "media-type" attribute is required for linked resources located in the EPUB container
- Default severity: Error

## Typical causes

- A metadata link to a local record or file written without media-type.

## How to fix it

- Add media-type with the linked file's format.

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EPUBLab.