What Is an NCX File in an EPUB and Do You Still Need One?
An NCX file (Navigation Control for XML) is an XML document inside an EPUB that defines the book’s table of contents for e-reading devices. It was required in EPUB 2 but has been deprecated since EPUB 3.0 in favor of an HTML-based navigation document. Most self-published authors creating EPUB 3 files today do not strictly need an NCX file, but including one remains a smart backward-compatibility measure for reaching older e-readers.
What Does an NCX File Actually Do?
The NCX file is a machine-readable map of your book’s structure. It tells the e-reader where each chapter and section begins so the device can render a clickable table of contents — typically displayed as a side panel or pop-up menu that readers access without leaving the current page.
Inside an EPUB archive, the NCX file is conventionally named toc.ncx. It uses XML syntax and contains a hierarchy of navPoint elements nested within a navMap. Each navPoint specifies a label (the text the reader sees, like “Chapter 3”) and a content source (the file and anchor location within the EPUB). An EPUB is simply a ZIP archive with a different extension, so you can inspect the NCX yourself by renaming any .epub file to .zip and extracting its contents.
The NCX itself is invisible to the reader during normal reading. It only appears when the reader invokes the device’s table of contents feature. This is different from an in-book table of contents page, which is a visible HTML page the reader can scroll through like any other part of the book.
How Did EPUB 3 Replace the NCX?
EPUB 3.0, released in October 2011, officially deprecated the NCX file and introduced the EPUB Navigation Document as its replacement. The NCX had served the EPUB 2 standard well since 2007, but its XML-only format had limitations — it could not be styled with CSS, could not serve double duty as a visible page in the book, and lacked support for internationalization features like ruby annotations.
The transition was not entirely smooth. EPUB 3.1, released in January 2017, broke backward compatibility with earlier EPUB 3 versions and was largely rejected by the publishing industry. EPUB 3.2, published in May 2019, restored full backward compatibility. The most recent version, EPUB 3.3, was published as an official W3C Recommendation on 13 January 2026 and maintains full backward compatibility with EPUB 3.2 and 3.0.1.
Throughout all these revisions, the NCX has remained in the same position: deprecated but still technically supported. The W3C lists it among “things that have been removed” from the core EPUB 3 specification, alongside DTBook, Tours, and the EPUB 2 meta element. However, reading systems are still permitted to process an NCX if one is present. This is why you will sometimes see advice to include both navigation systems in the same file — it is valid and causes no conflicts.
What Is the EPUB Navigation Document?
The EPUB Navigation Document is the modern replacement for the NCX file. It is an XHTML file that uses the HTML5 <nav> element to define the book’s table of contents structure. Unlike the NCX, which was purely a behind-the-scenes data file, the Navigation Document can serve dual purposes: it provides machine-readable navigation data for the reading system and it can appear as a visible, styled table of contents page within the book itself.
This dual-purpose design is one of the Navigation Document’s most practical advantages. In EPUB 2, authors often had to maintain two separate structures — the NCX for the device’s navigation panel and an HTML table of contents page for the reader. With the Navigation Document, a single file can handle both roles. You can apply CSS to control how it looks when displayed as an in-book page while the reading system simultaneously parses it for its navigation panel.
The Navigation Document also supports features the NCX could not, including embedded MathML and SVG within navigation links, ruby annotations for East Asian languages, and full CSS styling. For authors publishing in English, the most immediately useful improvement is the elimination of that redundant dual-TOC maintenance burden.
Do You Still Need an NCX for Backward Compatibility?
Strictly speaking, no — an NCX file is not required in any EPUB 3 publication. The EPUB 3 specification only requires the Navigation Document. However, including an NCX alongside the Navigation Document is still widely recommended in the EPUB authoring community, and for good reason.
Legacy e-ink devices — particularly older black-and-white, touchless-screen readers — can only process EPUB 2 files. These devices rely entirely on the NCX for navigation. If your EPUB 3 file lacks an NCX, a reader using one of these older devices may find the book has no usable table of contents at all. The original Kobo and Kobo Wi-Fi, for example, do not support EPUB 3.
The practical risk of omitting an NCX depends on your audience. If you are publishing a novel primarily sold through major retailers to readers using current-generation devices, the risk is low. If you are distributing widely — including to libraries, international markets, or niche readers who may use older hardware — including an NCX provides a safety net at essentially zero cost. Most EPUB authoring tools can generate both files simultaneously, so there is no meaningful extra work involved.
What Do KDP, IngramSpark, and Other Platforms Require?
None of the major self-publishing platforms explicitly require an NCX file for EPUB 3 submissions, but none prohibit its inclusion either. Here is what each platform expects:
- Amazon KDP: As of March 2025, KDP stopped accepting MOBI file uploads and now requires EPUB format. KDP processes your EPUB internally, and a valid EPUB 3 Navigation Document is sufficient. Including an NCX will not cause issues.
- IngramSpark: Accepts both EPUB 2 and EPUB 3 (flowable text) with a maximum file size of 100 MB. Their November 2025 File Creation Guide specifies EPUB 3.0 as the required format for new submissions. The NCX is not required but is accepted.
- Draft2Digital: Accepts pre-formatted EPUB files under 100 MB and does not alter the formatting of uploaded files. If your EPUB validates with the correct EPUB structure, it will be distributed as-is.
- Kobo: Supports EPUB 2 and EPUB 3. Note that the original Kobo and Kobo Wi-Fi devices do not support EPUB 3, which makes the NCX backward-compatibility argument particularly relevant for Kobo’s ecosystem.
- Apple Books: Fully supports EPUB 3 and the Navigation Document. An NCX is optional but harmless to include.
The bottom line for platform compatibility: build your EPUB 3 with a proper Navigation Document (this is required), and include an NCX as well if your tools make it easy to do so. No platform will reject a file for having both.
How to Create or Verify Your NCX and Navigation Document
If you are using a dedicated EPUB editor or conversion tool, the NCX file and Navigation Document are typically generated automatically. The key is knowing which tools handle this well and how to verify the result.
Sigil is a free, open-source EPUB editor that can generate both a toc.ncx and a Navigation Document. When you create or edit your table of contents in Sigil, it updates both navigation structures. Sigil also includes a built-in EPUBCheck validator, so you can confirm your EPUB structure is correct before uploading.
Calibre can convert between formats and generate EPUB files with both navigation systems. When converting from Word or other source formats, Calibre automatically builds the NCX from your heading structure. Its EPUB output options let you target EPUB 2 or EPUB 3 specifically.
Regardless of which tool you use, always run your final EPUB file through EPUBCheck — the official EPUB validation tool maintained by the W3C. EPUBCheck will flag missing navigation documents, malformed NCX files, and other structural issues. You can run it locally or use the online validator at the DAISY Consortium website. If you have previously dealt with images breaking during Word-to-EPUB conversion, you already know how valuable validation is for catching problems before they reach readers.
Frequently Asked Questions
What does NCX stand for in EPUB?
NCX stands for Navigation Control for XML. It is an XML file, conventionally named toc.ncx, that defines the hierarchical table of contents used by e-reading devices to display chapter navigation in EPUB 2 files.
Will my EPUB be rejected if it does not have an NCX file?
No. Major platforms like KDP, IngramSpark, Draft2Digital, and Kobo all accept EPUB 3 files with only a Navigation Document and no NCX. However, omitting the NCX means older e-readers that only support EPUB 2 will not be able to display your table of contents.
Can I have both an NCX and a Navigation Document in the same EPUB?
Yes. Including both is valid according to the EPUB 3 specification and is the recommended approach for maximum compatibility. Most EPUB authoring tools like Sigil and Calibre generate both automatically.
How do I check if my EPUB has an NCX file?
Rename your .epub file to .zip and extract it. Look for a file named toc.ncx, usually in the OEBPS or OPS directory. Alternatively, open the EPUB in Sigil and check the Book Browser panel, or run the file through EPUBCheck, which will report on all navigation components.
Is the NCX the same as the table of contents page in my ebook?
No. The NCX is a hidden, machine-readable file that powers the e-reader’s navigation panel or menu. A table of contents page is a visible HTML page within the book that readers can scroll through. In EPUB 3, the Navigation Document can serve both purposes simultaneously — acting as the machine-readable navigation source and appearing as a visible TOC page.
The NCX file in EPUB is a legacy component that served a critical role in EPUB 2 and still has value as a backward-compatibility measure today. For authors creating new EPUBs, the priority should be a well-structured EPUB 3 Navigation Document. If your authoring tool can generate an NCX alongside it — and most can — there is no reason not to include both.
