What you’ll need
Subject, preheader and optional message text.
Email TOOL · FREE TO USE
Subject Line & Preheader Tester
Review wording and approximate inbox truncation before sending.
Runs on your device · Files stay privateYour email workspace
How it works
Visible length, capitalization, repetition and selected wording checks.
Know the limits
Heuristics only: no predicted open rate, spam probability or exact email-client preview.
GET FROM A QUESTION TO A NEXT STEP
Get a clearer result with Subject Line & Preheader Tester
Review wording and approximate inbox truncation before sending. Subject, preheader and optional message text. Review the supported scope below before adding a large file or using the result in a campaign.
How to use Subject Line & Preheader Tester
Open Subject Line & Preheader Tester and inspect its input labels. Subject, preheader and optional message text.
Use the synthetic example where available, or choose your own supported file. Set the options deliberately; processing takes place in your browser.
Run the workflow, read any warnings and inspect the output. Download the result only after checking the values or file preview; clear the workspace when finished.
What do the results mean?
Visible length, capitalization, repetition and selected wording checks. Heuristics only: no predicted open rate, spam probability or exact email-client preview.
What to do next
Check a small representative input first. For exported assets, reopen the downloaded file in its intended application before using it in production.
Keep the scope in mind
Heuristics only: no predicted open rate, spam probability or exact email-client preview.
Common questions about Subject Line & Preheader Tester
Does Subject Line & Preheader Tester save my input?
This workflow uses browser memory. Downloads are saved by your browser, but tool inputs are not submitted to a server or stored by this tool.
What should I do if a result is unavailable?
Check the input format, units and limits. Heuristics only: no predicted open rate, spam probability or exact email-client preview. An unavailable result does not establish that a campaign, document or email address is valid or invalid.