Amazon never confirmed an algorithm called A10. A great deal of listing advice is built on it anyway.

Key takeaways

• A9 is Amazon's official name for its search algorithm. A10 is community terminology for the evolved version, and Amazon has never confirmed the name.
• The observable shift is real regardless of naming: weight moved from keyword matching and raw sales volume toward conversion — whether shoppers who land on the listing actually buy.
• Backend search terms are limited to 249 bytes, not characters. Special and accented characters will count as two bytes, and exceeding the limit will make Amazon ignore the entire field.
• Titles changed on July 27, 2026: 75 characters maximum in every category except media, with a new 125-character Item Highlights field that is indexed for search. Articles quoting 200 characters describe the January 2025 rule, which the July change replaced.
• External traffic is a ranking signal, with one estimate putting the contribution at 15% to 20%. Treat estimates of unpublished weightings as estimates.

Amazon has never published anything called A10. A whole genre of listing advice opens by telling you A9 is dead and A10 replaced it, and it is worth knowing what that claim rests on before you act on the rest of the article — because the shift the label describes is real, and the weightings people attach to it are invented.

01The naming problem, and why it matters

A9 is the official name of Amazon’s search algorithm. A10 is community terminology for the evolved version, and Amazon has never confirmed the name.

Another goes further and is worth quoting in substance: industry discussion of “A10” often uses the term “seller authority” to describe the combined effect of account health, fulfillment reliability, customer service, return patterns and sales history — and that source advises treating these as supporting trust and conversion outcomes rather than as a separately confirmed ranking factor.

That is a careful distinction and most content on this subject does not make it. When an article tells you a specific unnamed factor carries a specific weight in an algorithm whose name the vendor invented, it is describing an inference, not a specification.

Why this matters practically: it changes what you do when advice conflicts. If two sources disagree about a confirmed mechanic — the byte limit on backend terms — one of them is wrong and you can check. If they disagree about the weight of “seller authority”, neither is wrong because neither is measuring anything Amazon published.

02What the shift actually is

Strip the naming and the sources agree on the direction, which is what matters.

Away from: keyword density, title stuffing, raw sales volume as the dominant signal.

Toward: whether the listing satisfies the shopper. Conversion rate is described repeatedly as the primary signal — one source frames the question as “when shoppers land on your listing, do they buy?”

Consistently named factors:

Factor	Notes
Relevance	Exact-match keywords in title and bullets still drive indexing. Without relevance nothing else applies
Conversion rate	Described as the dominant signal in the evolved system
Click-through rate	Main image and title drive it; low CTR is signalling poor relevance
Reviews	Both a conversion factor and a ranking signal; quality, sentiment and velocity
Price	Affects conversion directly, therefore ranking directly
Inventory availability	Out of stock means no Buy Box, no conversion, and ranking erosion described as taking weeks to rebuild
Return rate	Named as a ranking input — which links directly to the returns guide
External traffic	Treated as a signal by most practitioners; one agency estimate puts the contribution at 15–20%, which is a guess about an unpublished weighting

Two of those are worth pausing on because they connect to costs covered elsewhere on this site.

Low stock hurts before you stock out. One analysis makes a specific point: raising prices to conserve remaining inventory drops conversion, and rankings decay before the stockout actually happens. That compounds with the low-inventory-level fee, which charges you per unit sold while thin. You pay a fee and lose rank simultaneously.

Return rate is a ranking input. Which means the Frequently Returned Item badge is not the only way returns cost you traffic.

03The mechanics you can actually verify

These are specifications rather than inferences, and they are where most listings lose free ground.

Backend search terms: 249 bytes. Not characters. most alphanumeric characters are one byte while special and accented characters count as two, and — the part that matters — exceeding the limit will make Amazon ignore the entire field, not just the overflow. A field that is silently not indexed is worse than an empty one, because you think it is working.

Amazon’s rules for that field:

• No repetition of words already in your title — indexing does not double
• Synonyms and alternative names shoppers actually use
• Common misspellings
• Relevant abbreviations
• No competitor brand names
• No punctuation needed; separate with spaces

Titles: two rules, one current. From January 21, 2025 Amazon capped titles at 200 characters, banned a set of special characters and limited word repetition. On June 10, 2026 it announced the next step: from July 27, 2026 titles in every category except books, music and video must be 75 characters or fewer, spaces included, and a new Item Highlights field takes up to 125 further characters that are indexed for search and shown under the title. Titles left over 75 are rewritten by Amazon’s AI; brand-registered sellers get 14 days in Review Listing Changes to edit the suggestion, everyone else gets it applied. Total indexable space stayed near 200; the split is what changed. An article quoting 200 characters is describing 2025.

The working position: check the current limit for your specific category in Seller Central before a title rewrite. This is exactly the kind of figure that changes and is not revisited in published guides.

Item Highlights, attribute fields and A+ Content are free indexing and free context left on the table when empty. Filling them costs an afternoon.

04What is now actively harmful

Reporting is consistent that several tactics that once worked now carry a penalty or waste space:

• Keyword stuffing. Described as reading as noise to shoppers and backfiring with an intent-based engine
• Sorting keywords by volume rather than conversion. Chasing impressions that never buy
• Repeating title words in the backend field. No additional indexing, and it consumes bytes
• Treating price and inventory as somebody else’s problem. Both are direct ranking inputs
• Publishing generated copy without review. One source is blunt: generic content that violates a policy is still your responsibility to fix
• Designing for desktop when most shoppers are on a phone

05PPC and organic rank

One claim deserves correcting because it circulates widely.

PPC does not guarantee an increase in organic rankings. It can improve visibility and generate sales and search-term data; organic position still depends on relevance, conversion, availability, price and customer experience.

The genuinely useful relationship is the reverse of how it is usually described: use PPC search-term reports to find which keywords actually convert, then build those into the title and backend terms. Paid discovers, organic keeps. Our PPC guide covers the cost side of that discovery.

06The order to work in

1. Fix relevance first. Without indexing on the right terms nothing else matters.
2. Fix the main image and title. They determine click-through, which is the first behavior measured.
3. Fix conversion. Images, bullets that answer questions rather than list features, sizing and dimension detail, A+ Content. This is the highest-weighted signal and it is entirely under your control.
4. Fill every field. Backend terms within 249 bytes, Item Highlights, attributes.
5. Then advertise. One source’s position is that for most independent sellers the highest-use change remains fixing listing quality first and considering advertising once the listing converts organically. That ordering is also cheaper.
6. Test changes rather than assuming. Amazon offers A/B testing for eligible listings. A conversion lift that does not move contribution profit is not a win — check it against the fee stack.

Export your titles from Manage All Inventory and sort by length. Anything over 75 characters has either already been rewritten by Amazon or is about to be — and if you have not looked at Review Listing Changes since July, someone else has been editing your listings.

Frequently asked

Is A9 or A10 the real algorithm?

A9 is Amazon's official name. A10 is community terminology for the evolved version and Amazon has never confirmed it. The underlying shift the term describes is real; the label is not Amazon's.

How many characters do I get in backend search terms?

249 bytes, not characters. Special and accented characters will count as two bytes, and exceeding the limit will make Amazon ignore the entire field rather than just the overflow.

How long can my title be?

75 characters including spaces, in every category except media, since July 27, 2026. A separate Item Highlights field carries up to 125 indexed characters. Titles over 75 are rewritten by Amazon; brand owners get a 14-day review window.

Does PPC improve organic ranking?

it does not guarantee it. PPC improves visibility and generates search-term data; organic position still depends on relevance, conversion, availability, price and customer experience. The useful move is mining PPC search-term reports for converting keywords and building those into the listing.

Does external traffic help?

It is a ranking signal, with one estimate putting the contribution at 15% to 20%. Treat estimates of unpublished weightings accordingly.

What is the single highest-use change?

Conversion. It is the dominant signal, it is entirely under your control, and it improves the economics of every advertising decision that follows.

Sources

1. New product title requirements effective January 21, 2025 (200 characters including spaces; banned special characters; word repetition limit), Amazon Seller Central, Seller Forums announcement Primary source accessed 2026-09-04
2. Updates to improve your product titles begin on July 27 (75-character cap in all categories except media; Item Highlights, 125 characters, indexed for search; AI rewrites with 14-day brand review), Amazon Seller Central, Seller News announcement, June 10, 2026 accessed 2026-09-04
3. Amazon's 75-character title limit: the complete guide (brand name counts toward the 75; Item Highlights keeps total indexable space near 200), ClearAds Secondary accessed 2026-09-04
4. Amazon A9 algorithm: how search ranking actually works in 2026 (A10 as community terminology never confirmed by Amazon; external traffic estimated at 15–20%; COSMO and Rufus; low stock eroding rank before stockout; PPC search-term reports feeding organic terms), Feedvisor Secondary accessed 2026-09-04
5. Amazon A9 algorithm: how Amazon’s search engine works (2026) (treating "seller authority" as supporting trust and conversion rather than a separately confirmed ranking factor; PPC not guaranteeing organic ranking), SalesDuo Secondary accessed 2026-09-04
6. How to optimize your Amazon listing for page 1 rankings in 2026 (249 bytes for backend search terms; two-byte special characters; entire field ignored if the limit is exceeded; conversion as the primary signal), SellerSprite Secondary accessed 2026-09-04
7. Amazon listing optimization 2026: A10 algorithm playbook (backend field rules: no repetition, synonyms, misspellings, abbreviations, no competitor brands, no punctuation; A/B testing changes), Nova Analytics Secondary accessed 2026-09-04
8. The complete Amazon listing optimization guide (2026) (75-character title deadline; keyword stuffing backfiring; sorting keywords by volume rather than conversion; empty fields as lost indexing; responsibility for generated copy), Foxtale Agency Secondary accessed 2026-09-04
9. Amazon listing optimization: the ultimate 2026 guide (titles measured in bytes rather than characters; weighting order of title, bullets, backend, description), Keywords.am Secondary accessed 2026-09-04
10. Amazon listing optimization: the complete 2026 guide (fixing listing quality before advertising as the highest-use change for independent sellers; compounding effect of conversion on ranking), Shotova Secondary accessed 2026-09-04
11. How to optimize your Amazon listing: complete 2026 guide (backend terms for synonyms and spelling variants; never repeating title words; keyword density as an A9-era tactic now penalized), Gracia Marcom Secondary accessed 2026-09-04