Email Subject Line Analyzer

Score your email subject line for open rate potential and spam risk.

Subject Line

Analysis runs entirely in your browser — nothing is sent to a server.

About Email Subject Line Analyzer

The Email Subject Line Analyzer scores your subject line out of 100 across six dimensions: character length (ideal is 41–50 characters), power words that drive curiosity and action, personalization tokens such as {first_name}, urgency and scarcity cues, a curiosity gap, and spam-trigger word detection. Bonus points are awarded for emoji usage. Writing your entire subject in ALL CAPS applies a penalty. Marketers use scores like these to predict open rates before sending. All analysis runs locally in your browser — your subject line is never sent to a server.

Built and maintained by Meet Shah · Last updated 5 August 2026

What this tool is used for

Checking a subject line's length against where mobile clients truncate.
Screening for words and punctuation that raise spam-filter risk.
Comparing two candidate lines before a send.
Checking whether a personalisation token leaves the line readable when it is empty.
Reviewing a line written by someone else before it goes to a list.

Frequently Asked Questions

How is a subject line different from a headline?: Different constraints entirely. It competes in a crowded inbox against known senders, it is paired with a visible preheader, and it is filtered by spam scoring — a headline faces none of these. Mobile clients also truncate far earlier.
How many characters actually show?: Around 30-40 on a mobile client, against 60+ on desktop. Since most email is opened on mobile, the effective budget is closer to 35 characters — much tighter than a web headline.
What is the preheader and why does it matter?: The preview text shown after the subject. If unset, clients pull the first text in the body — often "View this email in your browser", which wastes the single best piece of supporting copy you have.
Which words trigger spam filters?: Modern filters weigh sender reputation and engagement far more than keywords, so "free" alone will not sink you. What still hurts: ALL CAPS, multiple exclamation marks, excessive punctuation, and heavy currency symbols.
Do emoji in subject lines help?: They lift open rates in some audiences and reduce them in others, so it is genuinely an A/B question. Practical caveats: rendering differs by client, and a screen reader announces the full emoji name aloud.
Why does the same subject line perform differently across sends?: Because the subject is only one input. Send time, sender reputation, list segment and how recently the reader last engaged all move open rates more than wording does — which is why a single A/B result rarely replicates.
Is open rate still a reliable measure?: Less than it was. Apple's Mail Privacy Protection pre-fetches tracking pixels for its users, registering opens that never happened, so open rate now overstates engagement by a share that varies with your audience's client mix.

Common errors and gotchas

Optimising for a spam score rather than for the reader, when sender reputation matters far more than wording.
Using all-caps or heavy punctuation for urgency, which triggers filters and reads as shouting.
Ignoring the preheader, which the client shows next to the subject and often decides the open.
Assuming truncation happens at the same point everywhere, since it varies by client and device.
Promising something the email does not contain, which trains the list to stop opening.