Let your agent check every email before it ships

Courier’s Device Preview feature is presented as a way for AI coding agents to verify email templates visually across real desktop, mobile, and webmail clients before publication, addressing client-specific issues such as missing buttons, broken personalization, layout failures, dark-mode readability, and incorrect responsive ordering. Using Courier Skills, an API key, realistic test data, and a vision-capable model, an agent can inspect a draft, define expected content and section relationships, run previews on Courier’s recommended client set, download screenshots, evaluate each rendering with evidence-based PASS, FAIL, REVIEW, or N/A results, and fix confirmed draft-level problems without publishing. The post recommends GPT-6 Luna at high reasoning effort based on stated visual-reasoning benchmarks and cost comparisons, while noting that Claude Sonnet 5 may be preferable for OCR-heavy reviews and that users should test models against their own labeled examples. It supplies a detailed review prompt, guidance on examining full screenshots and overlapping high-resolution tiles, examples of bugs found in actual email previews, SDK-based workflows for targeted rechecks, and implementation advice such as preserving draft state, reusing identical test data, saving temporary screenshot links promptly, and distinguishing meaningful usability defects from harmless client rendering differences.

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