Amazon Backend Keywords: The 2026 Guide to Hidden Search Terms

Backend keywords are the easiest lever on Amazon that most sellers still get wrong. They're invisible to shoppers, take 10 minutes to update, and directly impact which searches your product appears for. Yet I'd estimate 70% of the listings we audit at GigaBrands have backend keywords that are either blank, stuffed with duplicates, or filled with terms that actually hurt indexing.

Here's everything you need to know in 2026 — character limits, what to include, what to avoid, and the lesser-known fields that most sellers don't even know exist.

What Are Amazon Backend Keywords?

Backend keywords (also called "search terms" or "hidden keywords") are text fields in your Seller Central listing that Amazon's algorithm reads but shoppers never see. They exist so you can include relevant search terms that don't fit naturally in your title, bullets, or description.

Think of them as metadata for Amazon's search engine. Your title and bullets are the public-facing copy. Backend keywords are the private-facing index.

Amazon's algorithm — historically called A9, now evolving into what Amazon internally calls COSMO (a more semantic, intent-based model) — uses backend keywords as one of several relevance signals when deciding which searches your product appears for.

Amazon Backend Keyword Character Limit in 2026

The limit is 250 bytes for the main Search Terms field. Not 250 characters — 250 bytes. This matters because:

• Standard ASCII characters (English letters, numbers) = 1 byte each

• Accented characters (é, ñ, ü) = 2 bytes each

• CJK characters (Chinese, Japanese, Korean) = 3 bytes each

For English-only sellers, 250 bytes effectively means 250 characters. If you're including Spanish, German, or other non-ASCII terms, count bytes, not characters.

If you exceed 250 bytes, Amazon may ignore the entire field. Not just the excess — the whole thing. This is one of the most common backend keyword mistakes and one of the hardest to catch because there's no error message. Your listing just silently stops indexing for those terms. How to check your byte count: Paste your keywords into a byte counter tool, or use this quick check in any browser console: `new Blob(["your keywords here"]).size`

What to Include in Backend Keywords

Your backend keywords should contain terms that are:

• Relevant to your product (obvious, but violated constantly)

• Not already in your title, bullets, or description (duplicates waste bytes)

• Actual search terms people use (not marketing language)

Specifically, include:

• Alternate spellings and common misspellings. "Tumbler" vs "tumblr." "Organizer" vs "organiser." Amazon's algorithm handles some of these, but not all.

• Synonyms your title doesn't cover. If your title says "water bottle," your backend could include "hydration flask," "drink container," "gym bottle."

• Spanish translations of your main keywords (if selling in US marketplace). Amazon US has a massive Spanish-speaking buyer base. "Botella de agua" costs you 18 bytes and opens a whole new search audience.

• Abbreviations and acronyms. "SS" for stainless steel. "BPA" if not in your title already.

• Use cases and occasions. "Birthday gift," "camping gear," "office desk accessories" — if those searches are relevant to your product but not in your visible copy.

• Size, color, and material variations you couldn't fit in your title.

Format: Separate terms with spaces. No commas, no semicolons, no pipes. Just spaces. Amazon treats the entire field as a space-delimited list of terms.

What NOT to Put in Backend Keywords

This list is critical. Including prohibited content can get your listing suppressed or reduce indexing:

• Your brand name. Already indexed from your brand field.

• ASINs or product identifiers. Against Amazon's policy.

• Competitor brand names. Explicitly prohibited and can trigger IP complaints. Amazon has gotten aggressive about enforcing this since 2024.

• "Best," "cheapest," "top-rated" or other subjective claims. Amazon filters these out.

• Temporary statements. "New," "on sale," "just launched." These become inaccurate and are filtered.

• Duplicate words already in your title or bullets. Amazon already indexes those. You're wasting bytes.

• Punctuation and stop words. "For," "the," "and," "with" — Amazon ignores these. Don't waste bytes on them.

• Repetitive terms. "Dog toy dog chew dog bone" — you only need "dog" once. Amazon doesn't weight by repetition.

The Backend Fields Most Sellers Don't Know About

The main "Search Terms" field gets all the attention. But there are additional backend fields that Amazon indexes, and almost nobody fills them out:

Subject Matter (5 lines)

Each line accepts up to 50 characters. This field tells Amazon what your product is about at a categorical level. Use it for broader category terms that don't fit in your search terms.

Example for a stainless steel water bottle:

• Line 1: hydration accessories

• Line 2: outdoor drinkware

• Line 3: fitness equipment accessories

• Line 4: sustainable reusable products

• Line 5: kitchen and dining

Intended Use

Describe how the product is used. Amazon uses this for relevance matching, especially with the COSMO algorithm's shift toward intent-based search.

Example: "Daily hydration for gym workouts, office use, outdoor hiking, and travel."

Target Audience

Who is this product for? Again, this feeds Amazon's relevance engine.

Example: "Athletes, fitness enthusiasts, office workers, outdoor adventurers, students."

Other Attributes

Depending on your category, there may be additional fields: Platinum Keywords (historically for vendors, now largely deprecated), Style Keywords, and various category-specific attribute fields. Fill out everything Amazon gives you. Every indexed field is free real estate.

How to access these fields: In Seller Central, go to your listing → Edit → Click "Keywords" tab. Some fields only appear in flat file uploads (Inventory File templates). If you don't see Subject Matter or Intended Use in the GUI, use a flat file to populate them.

How to Find the Right Backend Keywords

Don't guess. Use data.

1. Search Query Performance Report. In Brand Analytics, this shows you exactly which search terms are driving impressions and clicks for your ASINs. If a query is sending traffic but isn't in your listing copy, it belongs in your backend. 2. Reverse ASIN lookup. Tools like Helium 10 Cerebro or Data Dive show you which keywords your competitors rank for. Cross-reference with your own indexed terms. Any gaps = backend keyword candidates. 3. Amazon's auto-complete. Start typing your product's main keyword in Amazon's search bar. The suggestions are real, high-volume search terms. Capture relevant ones you're missing. 4. Your PPC Search Term Report. This is gold. It shows the actual queries shoppers typed that triggered your ads. Filter for converting search terms that aren't in your listing — those are backend keyword candidates with proven purchase intent. 5. Amazon Brand Analytics — Search Catalog Performance. Shows search terms by ASIN. Cross-reference to find terms Amazon associates with your product that you haven't explicitly targeted.

How Backend Keywords Interact with Amazon's Algorithm

A few things to understand about how Amazon actually processes these:

Amazon indexes the combination of all text fields. Title + bullets + description + backend keywords + subject matter + intended use = your total keyword footprint. Amazon can match multi-word queries by pulling one word from your title and another from your backend. You don't need exact phrase matches in a single field. Order doesn't matter. "Stainless steel water bottle" and "bottle water steel stainless" are equivalent in the backend. Don't waste bytes trying to create phrases. Indexing isn't instant. After updating backend keywords, it can take 24-72 hours for Amazon to fully reindex your listing. Don't panic if you don't see changes immediately. Verify indexing by searching for a unique backend term + your brand name on Amazon. COSMO changes the game. Amazon's COSMO algorithm is increasingly semantic — it understands intent, not just keyword matching. This means the Subject Matter, Intended Use, and Target Audience fields are becoming more important, not less. Filling them out accurately helps Amazon understand what your product IS, not just what words are associated with it.

Common Backend Keyword Mistakes (That Cost You Rankings)

Mistake 1: Exceeding 250 bytes without knowing it. Your listing silently deindexes for backend terms. Check byte count every time you edit. Mistake 2: Duplicating title keywords. If "stainless steel water bottle" is in your title, don't put it in your backend. You just burned 30 bytes for nothing. Mistake 3: Using commas or semicolons. Some sellers format backend keywords like "keyword1, keyword2, keyword3." Those commas eat bytes and do nothing. Use spaces only. Mistake 4: Never updating. Search behavior changes. New terms emerge. Competitors shift. Review and update backend keywords quarterly at minimum. Mistake 5: Ignoring the other fields. Subject Matter, Intended Use, and Target Audience are free indexing opportunities. Leaving them blank is leaving rankings on the table.

Want us to audit your backend keywords across your entire catalog? We've optimized keyword strategies for 50+ brands. We'll show you exactly what you're missing. Book a free strategy call: https://calendly.com/d/crft-5qs-x9w (for brands doing $50K+/mo on Amazon)

Hunter Harris is the founder of GigaBrands, an AI-assisted Amazon growth agency managing 50+ brands with over $205M in total Amazon sales.