Test your subject line and preheader
The subject is the only part of your message most people will ever read, and every inbox cuts it in a different place. Japanese makes it worse: a full-width character takes two columns, so a 30-character subject can be as long as a 60-character English one.
- Runs entirely in your browser
- Works offline
- No upload
- No sign-up
- No watermark
Loading the tool…
How it works
- Type or paste the subject.
- Add the preheader — the grey text the inbox shows after it.
- Check where each client cuts, and read the findings.
Why nothing is uploaded
Every operation on this page is done by code running inside your browser tab, using the same engine that renders web pages. The file is read from disk into your tab’s memory, transformed there, and written back out as a download. It is never sent anywhere — not to us, not to a third party.
Verify it yourself
- Open your browser’s developer tools (F12) and select the Network tab.
- Load your file and run the tool.
- The only requests you will see fetch the tool’s own code — and, for a few heavy tools, their open-source engine from a public CDN — plus one small page-view ping to loreatec.jp (page address and title, nothing more). None of them carry your file.
Frequently asked questions
Why measure width instead of characters?
Because clients cut by the space a character occupies, not by how many there are. A Japanese full-width character and an emoji each take two columns; a Latin letter takes one. Counting characters gives the wrong answer for exactly the languages where it matters most.
What is a preheader and why does an empty one matter?
It is the text the inbox shows after the subject, taken from the beginning of the message body. If you do not set one deliberately, the inbox shows whatever comes first in your HTML — very often “View this email in your browser”, or nothing at all. It is free space in the most valuable part of the screen.
Are emoji in subjects bad?
Not in themselves. One, used to make a recurring message recognisable in a list, works. Three or more reads as spam to both people and filters, some corporate gateways strip them, and a few older Japanese clients render them as tofu boxes. Also: they count as two columns each.
Does a flagged word mean my message will be filtered?
No. A single word is nothing — “free” in a genuine invoice is fine. What filters react to is a pattern: several words from the same category, plus urgency, plus an unauthenticated sender. The list here is a prompt to reread the line, not a verdict.