RSC-033 is reported as error by default. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.

EPUBCheck · Resources and references

EPUBCheck RSC-033: query string in a URL

Updated: Nov 4, 2026

EPUBCheck RSC-033 is an error message: “Relative URL strings must not have a query component, but found one in "…".” A relative URL contains a query string (?key=value), which EPUB does not allow because there is no server to answer it. The reading app looks for a file whose name includes the query and does not find it.

The official message

Relative URL strings must not have a query component, but found one in "%1$s".

Default severity: Error. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.
EPUBCheck version: 5.4.0

%1$s, %2$s… are filled in with the file, value or element EPUBCheck found.

Typical causes

Links copied from a website, such as page.xhtml?id=3.
Cache-busting parameters such as style.css?v=2 added by a build tool.

How to fix it

Find the URL named in the message.
Remove the query part from the URL; use a #fragment to point inside a document.
If a build step adds it, change the step, then validate again.

When it's not this

A #fragment on a stylesheet link is only the usage message RSC-013.

Terms used here

Other RSC messages

RSC-032 Fallback must be provided for foreign resources, but found none for resource "…" of type "…".
RSC-034 Scripts must have a JavaScript media type.
RSC-031 Remote resource references should use HTTPS, but found "…".
RSC-035 "…" is a legacy media type for JavaScript. Consider using 'text/javascript' instead.
RSC-030 File URLs are not allowed in EPUB, but found "…".
RSC-029 Data URL is not allowed in this context.

Sources

EPUB 3.3, §4.2.5 URLs in the OCF abstract container · read Nov 4, 2026

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.