If you've been waiting for a free book indexing solution, Cindex has heard you. In spring 2024, Scribendi — the software's longtime owner — announced it was open-sourcing Cindex under a CC0 public domain license, making it freely available to anyone who wants it. The community has since built a home for it at opencindex.org, and the original developer is involved in keeping it current.
This is genuinely good news. Cindex has been the industry standard for professional book indexers for decades. It's robust, precise, and now costs exactly nothing to download.
But "free software" and "the right tool for your project" aren't the same thing. Before you download it and start building your index, there are a few things worth understanding about what Cindex is, who it was designed for, and what it actually requires from you to produce a usable result.
What Cindex Is — and Who It Was Built For
Cindex wasn't designed with authors in mind. It was built for professional book indexers — the trained specialists who make their living creating indexes for publishing houses, university presses, and legal publishers. These are people who have typically spent months learning the craft of indexing, studied standards like the Chicago Manual of Style and NISO guidelines, and built up institutional knowledge about how to group concepts, structure subentries, and create cross-references that actually help readers navigate complex texts.
Cindex gives those professionals a powerful workspace. It handles alphabetization, manages see-also references, formats output to spec, and integrates with typeset PDF workflows. For someone who already knows how to index, it's an excellent tool that's now free. That matters to the professional indexing community enormously.
The question for self-published authors is different: can you use Cindex effectively without that background? The honest answer is: possibly — but probably not in the timeframe or with the ease you're hoping for.
What "Free" Changed — and What It Didn't
The CC0 license means you can download, use, and modify Cindex with no restrictions and no cost. That's a real change. As recently as 2023, Cindex cost several hundred dollars for a license, which put it out of reach for most self-publishing budgets on top of everything else production requires.
What didn't change is the software itself. Cindex is still a professional indexing tool built around a workflow that assumes you know what you're doing. You'll need to:
- Manually read through the typeset PDF and mark every indexable term as you go
- Create and manage your own entry hierarchy — deciding what becomes a main entry versus a subentry
- Build cross-references by hand based on your understanding of the manuscript's conceptual relationships
- Apply CMOS or publisher-specified style rules consistently throughout
The software tracks and formats what you enter. The intellectual work of deciding what to enter, and how to organize it, is entirely yours. That's not a criticism of Cindex — it's the point. The tool is a workspace for a skilled indexer, not an index generator.
The Real Cost: Time and Knowledge
Authors who've documented their experience using Cindex as a DIY solution report one consistent finding: it takes a long time, especially the first time.
A professional indexer working on a 250-page nonfiction book works at roughly 8–10 pages per hour — meaning a full book represents 25–35 hours of focused work. And they come to it with years of training that lets them make fast, correct decisions about entry structure and terminology. A first-time author attempting the same work typically takes significantly longer, because every decision requires deliberation: Is this term worth indexing? Should this go under the main concept or as a subentry? What's the right phrasing for the canonical entry?
The software cost being zero doesn't change the time equation. A 250-page business book indexed in Cindex by a first-time author working carefully is realistically a 40–60 hour project. For most self-published authors, that's a week or more of focused effort during the window right before a print submission deadline — which tends to be the worst possible time to take on a steep learning curve.
There's also the question of output quality. Professional indexes aren't organized keyword lists — they reflect editorial judgment about how readers will actually navigate the text. Developing that judgment takes time and practice. Most first-time authors who use Cindex produce something serviceable, but the gap between a careful first attempt and what an experienced indexer would produce is noticeable to anyone who's seen both.
The relevant comparison for most self-published authors isn't really "Cindex vs. hiring a professional indexer." Professional indexers charge $500–$2,000 for a typical nonfiction book and require a 2–4 week turnaround — a significant budget and timeline commitment many self-published authors can't accommodate. The comparison that actually matters is "Cindex vs. a purpose-built AI indexing tool."
Here's how they differ on the dimensions that matter:
Input requirement: Both require your final typeset PDF — not the manuscript, not the Word file, not a page-numbered draft. The index must be built from the formatted, paginated document where page breaks actually exist. This part is the same.
Who does the intellectual work: In Cindex, you do. You read the text, identify what's indexable, create the structure, and build every entry. In a purpose-built AI tool, the system identifies and surfaces the indexable terms, groups variants under canonical entries, builds an initial hierarchy, and generates subentries and cross-references — then hands you a review layer where you exercise editorial judgment over what it found.
Time investment: Cindex at full professional speed is 25–35 hours for a 250-page book. For a first-timer, realistically double that. AI-assisted workflows consistently run under two hours for the same book, including a thorough human review pass.
Learning curve: Cindex requires you to learn both the software and the craft of indexing. Purpose-built AI tools are designed so you don't need indexing expertise to produce a professional result — the system handles the structural decisions, and you focus on reviewing and refining.
Quality ceiling: Cindex in the hands of a trained professional indexer produces the best possible result. AI tools aren't at the same ceiling for complex academic or legal texts requiring deep specialist knowledge. But for trade nonfiction, business books, self-help, and most commercially published manuscripts, AI-generated indexes consistently clear the professional bar — accepted by publishers, useful to readers, properly formatted.
Total cost: Cindex is now free. AI indexing tools vary in pricing. But the right comparison includes your time. At a conservative $50/hour opportunity cost, 40 hours in Cindex represents $2,000 in time — more than the professional indexer you were trying to avoid.
Who Should Actually Use Cindex
Cindex is genuinely the right choice for specific situations:
Professional indexers who already know the craft and want a free, powerful workspace. The open-source transition is a significant gift to the professional indexing community, and the tool's capabilities are unchanged.
Authors who want to learn indexing as a long-term skill — people planning to publish many books and willing to invest the time to learn the craft properly, treating it as a durable capability rather than a one-time production step.
Publishers handling specialist technical texts — academic manuscripts, legal references, medical texts — where the conceptual complexity genuinely requires deep human engagement with the material that current AI tools don't fully match.
If none of those descriptions fit your situation — if you're a self-published author with one or two books, a timeline measured in weeks, and a need to produce a professional-quality index without becoming an indexing expert — Cindex being free doesn't change your calculus as much as the announcement might suggest.
What Self-Published Authors Actually Need
The news that Cindex is now free is real and worth knowing. It removes a genuine financial barrier for authors willing to invest the time to learn professional indexing software. If that's the path you want to take, opencindex.org has everything you need, and the community maintaining it is active.
But if what you actually need is a professional back-of-book index for a nonfiction manuscript — one that will pass editorial review, help readers navigate your book, and not consume a significant portion of your pre-launch bandwidth — the more relevant question isn't "can I get the software for free?" It's "what's the fastest path to a result I can be confident in?"
Onomastic is a purpose-built AI indexing tool that starts where professional indexers start: your final typeset PDF. Upload your manuscript, review the extracted entities, and produce a CMOS-compliant index with accurate page references, hierarchical entries, meaningful subentries, and cross-references designed for reader navigation — in under two hours.
Cindex being free is good news for the indexing world. It just doesn't change what most self-published authors actually need: a professional result on a realistic timeline, without a 40-hour learning project standing between them and their launch date.
