An index is a systematic guide that lets a reader find content in a book, made of headings representing topics, cross references between related terms, and locators pointing at pages. It sits at the very end of the back matter, it is built from final page proofs rather than from your manuscript, and it is almost never used in fiction.
It is also not a list of words, which is the single most common misunderstanding and the reason software cannot produce one.
The Definition, From the Standard
The American national standard for indexes, ANSI/NISO Z39.4-2021, defines it precisely:
"A systematic guide to facilitate retrieval of content. Indexes include the following major components: (a) headings representing topics or features; (b) cross-references or other linking devices among synonymous, equivalent, broader, narrower, and other related terms; (c) locators. An index serves as an information retrieval aid to the text or documents it accompanies."
There is an international standard too. ISO 999:1996, "Information and documentation. Guidelines for the content, organization and presentation of indexes", covers indexes "to books, periodicals, reports, patent documents and other written documents". It remains published and is flagged for revision.
The Society of Indexers, quoting ISO 999, describes an index as "An ordered arrangement of entries... designed to enable users to locate information in a document or specific documents in a collection".
Notice what all three definitions share: retrieval of topics, not occurrences of words. An index entry can point at a page where the concept appears and the word does not.
Does Fiction Need One
No. The standard says so directly. NISO Z39.4-2021 section 2.2:
"What kind of document requires an index? Generally, any document or collection of documents can be indexed with the possible exceptions of fiction and poetry."
The American Society for Indexing scopes its own guidance the same way, to "the traditional back-of-the-book index, found in printed non-fiction books", and maintains a page collecting indexed novels such as Nabokov's Pale Fire explicitly as literary curiosities rather than as a model.
If you are writing a novel, you do not need an index. What you may need is a table of contents, which is a different thing and, in an ebook, actually required.
Why Software Cannot Do It
This is worth being blunt about, because the market is full of tools claiming otherwise.
The American Society for Indexing's FAQ answers the question directly:
"The short answer is no. Computers can easily construct a concordance (a list of words or phrases and where they appear), but this is not an index, and is not very useful to someone looking for information. The so-called automatic indexing software programs being sold are simply not up to the task of indexing a book."
Both professional bodies have also published positions on AI. The Society of Indexers states: "We do not recommend the use of LLM-based AI tools for the indexing of books, or the use of indexes prepared in this way in books." The American Society for Indexing's statement on AI and book indexing, updated 25 March 2026, says that large language model tools "do not produce viable book indexes" and recommends "AI-generated indexes not be used in books."
The reason is structural rather than a matter of model quality. Indexing requires deciding what a passage is about, which is a judgement about the reader's likely question, not a property recoverable from the text's surface.
When It Is Made, and by Whom
From page proofs, not from your manuscript. An index points at printed page numbers, so it cannot exist until pagination is final. The Society of Indexers advises commissioning "well before the page proofs are back from the typesetter" and allowing "two or three weeks for a book of, say, 200 to 300 pages (50,000 to 70,000 words)". Yale University Press tells authors preparing their own that "you will need to do this during the same three or four weeks you are proofreading."
Usually the author's responsibility, usually delegated. The American Society for Indexing puts it plainly: "In the United States, according to tradition, the index for a non-fiction book is the responsibility of the author. Most authors don't actually do it." Columbia University Press tells authors that "Unless your contract specifies otherwise, it is your responsibility to supply the index" and "strongly recommends using a professional indexer". The Society of Indexers is more pointed: "unless an author is experienced in indexing, this is often unwise."
Cost. The Society of Indexers publishes recommended rates, which from 1 January 2026 are £34.00 per hour, £10.30 per 1,000 words, or £3.80 per page, with specialised texts normally costing more.
Length. The Society of Indexers suggests "around 3 to 5 per cent of the book's length (i.e. 7 to 12 pages for a 250-page book)". The American Society for Indexing gives 3 to 5 percent for a typical non-fiction book, 5 to 8 percent for history or biography, and 15 to 20 percent for reference works.
A Real Disagreement Worth Knowing
Indexes are alphabetised by one of two incompatible systems, and the authorities do not agree on which.
Word by word treats each word as the sorting unit. Letter by letter ignores the spaces and sorts on letters continuously. They produce different orders for any multi-word entry.
The Chicago Manual of Style now prefers word by word as of the 18th edition. Columbia University Press mandates the opposite, requiring entries "arranged dictionary style, in which each letter is the controlling unit, and not in phone-directory style, in which each word is the controlling unit", and this in a document that follows Chicago elsewhere.
NISO acknowledges the conflict and refuses to resolve it: "These standards are incompatible with one another. A single standard should be chosen as the authority for an index."
So pick one, apply it throughout, and tell your indexer which. Columbia adds a practical warning: word processors sorting alphabetically "often default to the phone-directory word-by-word system", so an automatic sort may silently pick a side for you.
Where It Goes
Last. In the Chicago Manual of Style's back matter sequence the index comes after the bibliography, the list of contributors and the illustration credits, with only a reading group guide, a biographical note, a colophon and errata able to follow it.
Back matter is numbered in the same arabic sequence as the text, so an index does not restart at 1. The full ordering is covered in ordering front matter and back matter.
What Deckle Does
Deckle has no index feature, and given everything above that is the correct scope for a novel writing application. An index belongs to non-fiction, is compiled from final page proofs by a person, and is delivered after typesetting rather than during drafting.
Deckle's back matter document types are About the Author, Acknowledgments, Also by the Author, Coming Next, Book Club Questions and Glossary. If you are writing non-fiction that needs an index, the workflow is to export the print PDF, send the paginated proofs to an indexer, and add the returned index as a final document before your last export.
For the back matter element Deckle does support, see what is a glossary in a book, and for the wider set, what is back matter in a book.
Common Mistakes
- Asking software to generate it. Both professional bodies say the output is not an index.
- Indexing from the manuscript. Locators need final pagination, so it waits for page proofs.
- Putting an index in a novel. The standard names fiction as an exception.
- Mixing alphabetisation systems. Word by word and letter by letter give different orders. Choose one.
- Leaving it to the end of the schedule. Commission before proofs arrive, not after.
- Assuming the publisher pays. Where a publisher hires the indexer, the fee is often deducted from author earnings.
FAQ
Q: Is an index the same as a concordance? A: No. A concordance lists words and where they appear. An index guides a reader to topics, including topics discussed without the obvious word.
Q: Can I write my own index? A: You can, and traditionally it is your responsibility. Both professional bodies advise against it unless you have the training.
Q: How long does indexing take? A: Two to four weeks for a typical book, according to the Society of Indexers and Yale University Press respectively.
Q: Does an ebook need an index? A: Page-based locators do not survive reflow. Ebooks generally rely on search and linked entries instead.
Q: What does an index cost? A: The Society of Indexers' 2026 recommended rates are £34.00 per hour, £10.30 per 1,000 words, or £3.80 per page.