Claude Opus 5.5 Email Preheader Review: Stop Stray Preview Text

Ask Claude Opus 5.5 to compare the intended preheader with the delivered email source and actual inbox preview. If a product launch shows navigation, repeated brand text or image descriptions beside its subject, rewriting the subject alone will not identify the source. Separate a copy decision from a template or client-rendering issue.

Start with the observed mismatch

Mailchimp's preview-text guidance explains the sender-controlled field and the fallback to message content. The Stacks email FAQ also describes body and image-alt text filling available preview space. These explain why the source must be checked; they do not establish a universal inbox length or guarantee that every recipient sees your exact string.

A launch-message example

For a fictional cup launch, the subject is “Meet the pocket cup.” A useful complementary preview is “A folding handle for smaller bags.” The opening body sentence can continue the same fact, so that additional extracted text remains coherent. This is an editorial example, not measured open-rate uplift. Do not invent a discount or deadline just to make the preview more persuasive.

Keep meaningful image alternatives. Replacing a product image's alt text with unrelated promotional copy may hide one symptom while making the message less useful when images are unavailable. Prefer the sender's supported preview field. If the template contains a dedicated hidden preheader, examine the actual generated HTML before changing its hiding styles or inserting long strings of special whitespace.

A complete diagnostic prompt

Review this product email's preview text. Inputs: approved product facts, subject, intended preheader, template, delivered HTML/plain-text parts if available, and an inbox screenshot with client/version/date. Do not send anything.

Locate where the intended preheader enters the generated message. Compare its exact value with the visible preview and identify likely extra text sources. Separate missing template binding, personalization fallback, copy redundancy and client-specific extraction. Missing delivery evidence remains unknown.

Return a diagnosis table, two subject/preheader pairs grounded only in approved facts, and the smallest template change if evidence supports one. Preserve meaningful image alt text and unsubscribe controls. Do not promise a fixed visible length or an open-rate increase. Define checks for a populated name, empty name, images disabled, desktop and mobile; distinguish editor preview from actual delivered results.

Use the official Opus guide for model context. This is a proposed review workflow; no model or mailbox test is claimed here.

Acceptance without invented guarantees

Record the approved pair, rendered source, recipient test state and observed inbox excerpt separately. Use only authorized test recipients. The release passes when the message source is correct and the agreed target clients have been checked, with any differing output documented. A preview that looks good in one inbox is evidence about that inbox only.

**How many characters should I write?** Put the useful detail first and test the target clients; character count is not a universal pixel budget.

**Can I force every client to show only my preheader?** This workflow provides no such guarantee. Keep the next body sentence useful as well.

**Does a clearer preview prove higher conversion?** No. That requires a properly measured campaign comparison.

Create the matching product visual in Panelly Studio after approving the message. For color changes inside the email itself, use the separate dark-mode review. Panelly is not represented as an email sender or native Opus integration.

Sources and further reading

• Original reference · mailchimp.com
• Original reference · v2.stackoverflow.design
• Original reference · platform.claude.com