This is a representative preview, not a live inbox test. Actual rendering varies by client version, device, settings, personalization, sender reputation, and message markup.
This tool runs locally in your browser.
Results are estimates based on your input only; entered values and result contents are not stored by BoringToolsKit.
Your inputs and results stay in this browser. This page may send privacy-bounded aggregate interaction events described in Privacy; it does not send your entered values or result contents.
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What does this tool show?
Email preview tester: check how your subject line and preheader render in Gmail, mobile inboxes, and truncated views before you send. Free, no signup.
How this calculator works
Formula
The simulator removes unsupported control characters, applies a documented character budget for the selected representative viewport and client card, and adds an ellipsis when a subject or preheader exceeds that simulation budget.
Worked example
Enter a sender name, Subject A, an optional Subject B, and preheader text. Switch between compact mobile, wide mobile, and desktop to compare how the same copy may truncate in four representative inbox layouts.
Assumptions to verify
- Character budgets are deterministic BTK simulation limits, not measurements of every live inbox client.
- Actual display varies with client version, device, settings, personalization, sender reputation, and email markup.
- The tool evaluates presentation only. It does not send email, inspect HTML, score spam risk, or predict inbox placement or deliverability.
Frequently asked questions
Does this send my email content anywhere?
No. The preview runs in your browser and does not upload, send, or automatically store the sender, subject, or preheader.
Is this an exact Gmail, Apple Mail, Outlook, or Yahoo rendering test?
No. These are representative layouts with documented simulation budgets. Live clients can display different text lengths and styling.
Does a good preview mean my email will reach the inbox?
No. Presentation and deliverability are different. This tool makes no spam, reputation, placement, open-rate, or delivery prediction.
Cite this tool
BoringToolsKit. “Email Preview Tester.” boringtoolskit.com/email-preview-tester/ (reviewed July 2026). Free to reference in articles, syllabi, and answer posts with a link.
Privacy: Inputs and results stay in this browser. Any future sponsored recommendation or advertisement will be clearly labeled and kept separate from the calculation.