Amazon Japan Listing Optimization: The Compliance Layer That Decides What You Can Say

Most "Amazon Japan listing optimization" advice translated from an English-market playbook treats the product title, bullet points, backend search terms and A+ Content as a pure ranking and conversion problem: pack in keywords, make a bold claim, test the copy, iterate. On Amazon.co.jp, three separate systems get a vote on that copy before ranking matters at all — Japan's Act on Securing Quality, Efficacy and Safety of Products Including Pharmaceuticals and Medical Devices (薬機法, commonly Yakuji-hō), the Act against Unjustifiable Premiums and Misleading Representations (景品表示法, Keihyō-hō), and Amazon's own published content rules for each field. None of the three care how well the listing converts.

This guide works field by field — title, backend search terms, A+ Content — through what each law and Amazon's own published guidance actually permits, with the exact statutory text and the exact platform rule cited rather than paraphrased. For the full table of prohibited and compliant cosmetic and skincare claims under Yakuji-hō, see our companion guide, Yakujiho Compliance: The Legal Red Lines for Beauty and Skincare in Japan — this article focuses specifically on where those restrictions collide with the mechanics of Amazon listing optimization. One note up front: LAUNOVA is an e-commerce operations agency, not a law firm. Nothing here is legal advice; classification and claim review for your specific product should go to qualified Japanese counsel or a registered Yakuji-hō compliance consultant.

Yakuji-hō: The Ceiling on What Your Title, Bullets and A+ Copy Can Claim

Article 66, paragraph 1 of Yakuji-hō prohibits, for any pharmaceutical, quasi-drug, cosmetic, medical device or regenerative medicine product, advertising, describing or circulating false or exaggerated statements about its name, manufacturing method, efficacy, effect or performance — "明示的であると暗示的であるとを問わず" (whether explicit or implicit). Paragraph 2 extends the same prohibition to any statement that could be mistaken for a guarantee of efficacy by a doctor or other professional. Article 68 goes further for anything not yet approved: no person may advertise the name, manufacturing method, efficacy, effect or performance of a drug, medical device or regenerative medicine product that has not received the required approval under Articles 14, 23-2-5, 23-2-23 or related provisions — an absolute bar, not a "be careful" one.

For listing optimization specifically, the practical effect is that the two things that make English-market copy persuasive — stating an outcome ("whitens skin," "reduces wrinkles") and implying it works better than it looks like it should — are exactly what Article 66 targets. It applies identically whether the claim sits in the visible product title, a bullet point, the description, or A+ Content text and imagery; the statute does not distinguish by field. It is also a strict-conduct restriction, not a truthfulness test: Article 66 does not require the claim to be false, only exaggerated or capable of implying a professional guarantee, which is a materially lower bar than most sellers assume when translating home-market copy.

Keihyō-hō: Why "No. 1," Discount Claims and Comparisons Need Evidence on File

Keihyō-hō applies to every product category on Amazon Japan, not only regulated cosmetics and supplements, which is what makes it the broader trap for general listing optimization. Article 5 prohibits two categories of misleading representation. Item 1 — 優良誤認表示 (misleading quality representation) — bars showing a product's quality or content as markedly better than it actually is, or markedly better than a competitor's, in a way likely to improperly induce customers and impair their ability to choose rationally. Item 2 — 有利誤認表示 (misleading advantageous-terms representation) — bars the same kind of misrepresentation applied to price or other transaction terms, such as claiming a discount, sale status, or price advantage over competitors that does not reflect reality.

The listing-optimization phrases that trip this most often are exactly the ones that read as persuasive copy: "業界 No.1" (industry No. 1) without a named, verifiable ranking source; "最安値" (lowest price) without an actual price comparison; a struck-through "reference price" that was never really the selling price; or a bullet point implying the product outperforms named or implied competitors. None of these require intent to deceive — Article 5 is a strict prohibition on the representation itself.

Keihyō-hō also has teeth specifically aimed at unsupported superlative claims. Article 7, paragraph 2 lets the Consumer Affairs Agency Commissioner demand, within a set period, the reasonable evidentiary materials backing any representation under review for a possible Item 1 violation — and if the business does not produce them, the representation is treated as a violation for purposes of a cease-and-desist order under that same provision. The Enforcement Rules fix that period at 15 days from the date the demand is delivered (Cabinet Office Order No. 6 of 2016, Article 7, paragraph 2), with an exception only where the business had a legitimate reason for missing it. This is the specific mechanism, commonly called 不実証広告規制 (the unsubstantiated-advertising rule), that turns "we believed it was true" into a non-answer: what is required is dated, methodology-matched evidence for the exact wording used, produced inside two and a half weeks.

The financial exposure sits in Article 8: a violation of Article 5 (excluding the Item 3 category, which covers separately designated representations) triggers a mandatory administrative surcharge of 3% of the sales generated by the non-compliant listing during the violation period — unless the calculated amount is under ¥1.5 million, or the business can show it neither knew nor had reason to know the representation was false and exercised reasonable care. Three percent sounds modest until it is applied to a listing's full sales run during however long the violation was live, on top of the cease-and-desist order under Article 7 and whatever ranking history a resulting takedown costs.

The Product Title Field: Ranking Signal Inside a Compliance Boundary

Amazon's own published guidance for Amazon.co.jp sellers recommends a title length of roughly 60 characters, kept under 80 (sell.amazon.co.jp, "Amazon SEOガイド"), built around a consistent formula: brand or manufacturer name + generic product name + features (specification, color, size, type) + model number or capacity/weight. That structure is a ranking recommendation, not a legal one — but it happens to leave very little room for the kind of subjective claim language that creates Yakuji-hō or Keihyō-hō exposure. The same official guidance separately instructs sellers not to use subjective comments like 「人気商品」 (popular product) or 「ベストセラー」 (bestseller) in the title — which is Amazon's own platform rule arriving independently at close to the same place Keihyō-hō's 優良誤認 restriction would: an unverifiable superiority claim in a title is a liability whether or not Amazon or the Consumer Affairs Agency is the one to flag it first. Category-specific title character limits and additional restricted terms exist inside Seller Central's own registration guidelines, which sit behind a seller login and could not be independently verified for this article — confirm the current limit for your specific category directly in your account before finalizing a title.

The practical build order that avoids rework: classify the product's regulatory category first (regular cosmetic, quasi-drug candidate, regular food, or unregulated general merchandise), draft the title using only claims permitted for that category, then optimize word order and keyword placement within that already-compliant draft. Optimizing keyword density first and then trying to "soften" an illegal claim after the fact routinely produces exactly the vague, hedge-everything copy that converts poorly — the compliant vocabulary has to be the starting material, not a patch.

The Backend Search Terms Field: Invisible to Buyers, Not Invisible to Amazon's Policy

The backend search terms field (検索キーワード, sometimes called Generic Keywords) is not shown to buyers and exists purely to catch search queries the visible title, bullets and description do not already cover. Amazon's official rules for this field, published on sell.amazon.co.jp, set a hard limit of under 500 bytes for most categories, tightened to under 250 bytes for Fashion & Apparel Accessories, Shoes & Bags, Jewelry, and Watches — with the string length calculated excluding half-width spaces and the separator characters comma, semicolon and period, and one full-width Japanese character averaging roughly 3 bytes. Terms must be separated by half-width spaces, must not duplicate anything already registered in the title, description or brand name fields, and — the part most relevant here — must not include: other companies' trademarks or similar/competing product names or product codes (the guidance names JAN, ASIN and UPC codes specifically); subjective expressions, with 「最高な」 ("the best") given as the example; or temporary-status expressions, with 「新商品」 ("new product") and 「セール中」 ("on sale") given as the examples.

Notice what that prohibited list actually is: it is the same category of claim Keihyō-hō Article 5 restricts in visible copy — unverifiable superiority language and false transaction-status claims — banned again in a field consumers never see. Whether a hidden backend field independently meets the legal definition of a consumer-facing 表示 under Article 5 is a separate legal question this article is not resolving. What matters practically is that the answer does not need to be resolved: Amazon's own content policy bans stuffing "セール中" or a competitor's brand name into search terms regardless of the Keihyō-hō question, and Amazon enforces its own rules independent of any regulator. The safe operating rule for the field is the same one that applies everywhere else in the listing: register upper-level category terms, synonyms and script variants (romaji/kanji/hiragana/katakana) that genuinely describe the product, and treat anything you would not be willing to defend as a public claim as off-limits here too.

A+ Content: Where the Same Claims Carry Into Images

A+ Content (商品紹介コンテンツ) is free to any seller enrolled in Amazon Brand Registry and combines images with text to communicate a product's features, differentiation and appeal beyond the standard bullet points. Amazon's own published guidance states that adding A+ Content to a product detail page produces an average 5.6% increase in sales (Amazon internal data, 2020, cited on sell.amazon.co.jp) — which is precisely why A+ modules tend to carry the boldest claims on the entire listing: sellers correctly treat it as the highest-leverage real estate on the page, and push harder there than they would in a plain text field.

That leverage cuts both ways under Japanese law. Yakuji-hō Article 66 and Keihyō-hō Article 5 do not distinguish between a claim written as a sentence and the same claim rendered as text inside a designed image — a before/after comparison graphic, a callout box reading "最高品質" (highest quality), or an infographic implying a therapeutic effect all carry identical enforcement exposure to the equivalent sentence in the product description. Every module in an A+ layout needs the same two-part check applied to the title and bullets: confirm the claim sits inside the permitted vocabulary for the product's regulatory category (see the full compliant-alternative table in our Yakujiho compliance guide), and confirm any superiority or comparison claim has evidentiary backing on file before the design work starts — not as a review step after the visuals are finished, when reworking an approved design costs real time and, per Amazon's own A+ Content guidelines, restarts the review queue.

DIY or Delegate? A Five-Question Decision Block

Whether to run this compliance layer in-house or hand it to an agency comes down to five practical questions, not a general preference for control or cost:

1. Do you have someone who reads the actual Japanese claim, not the English draft it was translated from? Machine-translated copy carries a violation across the language barrier intact — a phrase that is ordinary marketing language in English or Chinese can be an Article 66 or Article 5 violation once it lands in Japanese. If nobody on the team can read and evaluate the final Japanese wording against the permitted-claims framework, DIY starts from a blind spot that no amount of keyword optimization fixes.
2. How many SKUs and categories are you managing? A single SKU in an unregulated category (general merchandise with no health, beauty or efficacy angle) carries limited Yakuji-hō exposure and is a reasonable DIY candidate. Multiple SKUs spanning cosmetics, supplements and general goods multiply both the regulatory categories to track and the number of listings a single missed claim can affect.
3. Can you absorb a takedown during the learning curve? A first listing written and corrected in-house will likely go through at least one round of trial and error against the claim boundary. If a temporary suppression or takedown during that process is tolerable — low sales velocity, early launch stage — DIY iteration is viable. If the listing is already carrying meaningful sales volume, the cost of losing accumulated ranking and review history during a correction cycle usually outweighs the cost of a compliance review upfront.
4. Is your evidence file ready before you make a claim? Because Article 7(2)'s 15-day evidence window starts the moment the Consumer Affairs Agency asks, "we'll pull the data together if asked" is not a real strategy — the underlying test data, clinical results, or survey methodology needs to exist and match the exact claim wording before the claim goes live, not after a demand letter arrives. If that documentation discipline is not already part of your listing workflow, it needs to be built before optimization work continues, whether in-house or through a partner.
5. Do you need ongoing quarterly review, not a one-time launch check? MHLW guidance and Amazon's own content policies both change, and a listing that was compliant at launch is not guaranteed to stay that way. A DIY process needs a standing calendar commitment to re-check live listings; an agency relationship built around Amazon Japan operations should already include that cadence as part of the engagement rather than as a separate ask.

If most of these point toward DIY — a small, unregulated-category catalog, in-house Japanese reading capability, and tolerance for early-stage iteration — the compliant path is to classify the product, build titles and A+ Content from the permitted-claims framework outward, and keep evidence on file for anything comparative. If most point the other way — regulated categories, multiple SKUs, sales volume already at stake, or no in-house Japanese compliance reader — the cost of a wrong claim on a live listing typically exceeds the cost of having someone run the title, search terms and A+ Content review as part of ongoing Amazon Japan management.

We run Amazon Japan listings, A+ Content, backend search term strategy and sponsored ads as one connected workflow for overseas brands, with the compliance check built into the listing-build process rather than treated as a separate legal sign-off. If that connective layer is the gap on your side, see our Amazon Japan seller support scope or tell us where your current listings stand.