I bet that if you’re reading this, you’ve always accepted 500 characters as the gold standard for maximizing book visibility through search - work your way up to 500 characters and you’ve joined the metadata elite. You've surpassed the majority of publishers who add only two or three hundred keywords, or gasp, don’t add keywords at all. Well, dear reader, if your ONIX makes its way to Amazon, and Amazon is an important retailer for your sales, I have some news for you:
If you only send 500 keyword characters to Amazon, you’re probably missing out on sales.
Contrary to what you may have been told, Amazon accepts and uses far in excess of 500 characters per book. In this post we’ll uncover the origin of the 500 character limit, and provide actual hard data that shows Amazon does indeed accept keywords far beyond the 500 character limit. (In case you’re wondering why more keywords are better, the short answer: more keywords = more chances for a book to be found in search = more sales opportunities. A longer explanation is available here).
The "Best Practices For Keywords" Recommendation
The BISG’s metadata keyword best practice standard states a recommended limit of 500 characters. The guide is a fine document, and I highly recommend you give it a read in case you haven’t come across it before. I was a member of the committee who authored the document and contributed to it's content and discussions. If you’re tasked with “creating keywords for online retailers”, you should absolutely use this resource as a guide. When it comes to keywords destined to Amazon, it’s worth noting that: Amazon wasn't involved in authoring the standard, and the “best practices” are a general recommendation to the industry as a whole. They’re not prescriptive, and retailers can implement anything they wish to. In fact the committee, correctly, ensured they weren’t too Amazon-centric in their recommendations. Long story short - even though 500 characters is the “recommended” limit, it doesn’t require Amazon or any other retailer, to strictly abide by the recommendation.
Where Did The 500 Character Limit Come From?
I asked this question on the committee and the best answer I received was: “it’s always been in the ONIX standard”. As someone who has lead teams to build book search engines, I wanted to understand what the technical rationale might be - was there some data science based research that underpinned this widely accepted “best practice”? My search led me to the good folks over at EDItEUR who oversee the ONIX standard globally. From my exchanges with these publishing metadata veterans, I learned that:
- The keyword character limit as it’s defined in ONIX, has always been a “suggested limit”.
- The ONIX standard places no limit on how many keyword characters an ONIX sender can transmit.
- Publishers should rely on receivers (such as retailers) accepting at least 500 characters.
- The limit used to be 100 characters and was then raised to 250 before the current suggestion of 500.
- The 500 limit considers old library systems that may not have the technological resources of retailers, and therefore are limited in what they can receive.
Again, a sensible limit to accommodate myriad publishing systems of various sophistication levels and vintage. But also, still nothing prescriptive about what a receiver (retailer) should do with a keyword field, other than accept at least 500 characters.
It's Easy To Test The Limit, But You Have To Do It Properly
Search technology is complex and doesn’t operate in the same manner as say, a bank transaction system. If you login to your online banking website and send money to someone, they better receive it. Every cent needs to be managed, accounted for and then auditable by all parties involved. Search engines are somewhat different. When a search engine indexes data, while it may read everything available to it, the use and visibility of the source data comes down to a whole host of factors which is far beyond the scope of this post. Suffice to say that if you supply Amazon with say 100 keywords, it will read all of them, but won’t necessarily use all of them for your book (understand more about this here). If your character length test involves typing in each of your keywords into Amazon search, paging through countless results to check for your book, then using the absence of your book in results as evidence that the keyword wasn’t indexed - you’re doing it wrong. (We haven’t even touched on partial term matches). Each keyword is an opportunity, not a guarantee.
Cold, Hard, Data: How Many Keyword Characters Should I Provide?
Running a test to correctly identify whether a keyword improves search rank, involves analyzing hundreds of books, removing words found in the title, author names and category (BISAC/browse node) names from test queries and also searching for combinations of individual keyword terms (as a metadata expert, you already know that exact keyword matches are the tip of the search iceberg). We did all of this and here’s what we found:
Amazon indexes at least 1500 keyword characters from the keyword field in an ONIX file (or uploaded directly using Amazon's internal tools).
Kadaxis clients receive up to 1500 keyword characters, so this is the limit we tested. (On average, our clients receive an average of 1000 keyword characters per book). We found books matching search queries all the way up to the high 1400s character count after stripping away other metadata data we know is indexed. This approach gives us confidence that the book’s presence in search is attributed to the keyword and not other sources (like BISAC names).
30-50% of searches matched keywords were found in the 500-1500 character range
Said another way: if you’re only adding 500 keyword characters, your book is missing out on matching to 30-50% of search queries, than if you’d used 1000+ characters.
Books with 1000-1500 keyword characters match 67% more search queries, compared to books with 500 characters or less.
One of our tests compared 100 books from two trade publishers - one with Kadaxis keywords, and one who used an alternative service that maxes out at 500 characters. Both sets included a mix of good selling fiction and non-fiction titles and were run through identical measurement systems. The Kadaxis publisher had an average of 1098 keyword characters (max 1500) which matched to 67% more search queries than the publisher who added an average of 446 keyword characters (max 500).
Let's look at a couple of examples to illustrate further:
Title: Medical-Surgical Nursing Made Incredibly Easy (Incredibly Easy! Series)
This medical text matched numerous keywords in search, but one example of note is the keyword phrase "advanced pathophysiology". Neither of these terms are found anywhere in the book's metadata (as an aside, while this keyword is also not in the description text, know that the description isn't indexed for Amazon search, but that's a post for another day).
The keyword itself is present in the keyword field at character position 964 (out of 1079 total keyword characters). We can find the book in the Books search engine on Amazon for the search query "advanced pathophysiology, wedged between two other pathophysiology books. Note, the term is relevant for people interested in the topic, as evidenced by review mentions.
Let's take a look at one more example:
TITLE: The Greatest Story Ever Told--So Far: Why Are We Here?
Again, this title matches numerous keyword derived search queries, but we'll focus on one keyword: "heisenberg uncertainty", which refers to Werner Heisenberg's Uncertainty Principle. This keyword isn't mentioned anywhere in the book's metadata, but is mentioned several times by readers, including examples where "The Greatest Story Every Told" helped readers to better understand Heisenberg's Uncertainty Principle.
The keyword "heisenberg uncertainty" is present in the book's keyword field at character position 1101, and the book is found in the search results among related titles.
A few other examples, from hundreds in our set:
- Blockchain Revolution: How the Technology Behind Bitcoin Is Changing Money, Business, and the World. Keyword with search match: "smart contracts", character position 1142.
- The Perfect You: A Blueprint for Identity. Keyword with search match: "neuroscience", character position 1267 (actually matches 5 search queries about neuroscience).
- Darkfever (Fever Series, Book 1). Keyword with search match: "male characters", character position 1095.
What does this all mean? More keywords equals better search visibility, which equals more chances to sell (after all, most books are sold through Amazon search).
Keyword ROI: It’s Worth It
1000 characters is a lot of work, 1500 characters even more so, but compared to the rest of the effort and expense that goes into making a book a success, it’s a comparably small investment for the potential upside - especially when you consider the compounding value better search visibility earns a book. If you have questions about how we conducted our tests, how you can replicate our results or to learn more about our keyword services, please get in touch via the Contact form.
Thank you to the folks at Firebrand (Catherine Toolan, Steve Rutberg and Joshua Tallent) for their help with this article.