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; no data is stored.
No data is stored or transmitted.
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What does this calculator estimate?
Preview sender, subject line, and preheader truncation across representative inbox layouts. Runs privately in your browser.
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.
Privacy: Inputs and results stay in this browser. Any future sponsored recommendation or advertisement will be clearly labeled and kept separate from the calculation.