# EPUBCheck HTM-025: unregistered URI scheme, how to fix it

Source: https://epubcc.com/epubcheck/htm-025/ (updated 2026-11-04)

EPUBCheck HTM-025 is a warning message: “Non-registered URI scheme type found in href.” A link uses a URI scheme that is not registered. EPUBCheck warns because reading apps may not know what to do with it; the book stays valid.

- Official message (EPUBCheck 5.4.0): Non-registered URI scheme type found in href.
- Default severity: Warning

## Typical causes

- A typo in the scheme, such as htp: or http;.
- An app-specific scheme copied from a website or a document management system.
- A Windows path or a local file reference written as a link.

## How to fix it

1. Open the file EPUBCheck names (the message gives the path, line and column) in a text or EPUB editor such as Sigil, or unzip the EPUB and open it there.
2. Correct the scheme to http, https, mailto or another standard one.
3. If the link only worked inside one app or on the author's computer, remove the link and keep the text.
4. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If the link is empty (href=""), that is HTM-045, not HTM-025.

## Sources

- EPUB 3.3, §3.8 File URLs: https://www.w3.org/TR/epub-33/#sec-file-urls (read 2026-11-04)
- EPUBCheck 5.4.0 message texts (MessageBundle.properties, w3c/epubcheck on GitHub): https://github.com/w3c/epubcheck/blob/v5.4.0/src/main/resources/com/adobe/epubcheck/messages/MessageBundle.properties (read 2026-11-04)

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