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Test your email subject line and get a score out of 100. Analyze length, spam triggers, power words, personalization, emoji usage, readability, and question format with actionable recommendations to boost open rates.
Use BrandJet's free email subject line tester to check whether a subject line is clear, appropriately structured, readable, personalized where relevant, and free of obvious copy risks before you send it. The tool currently evaluates seven documented areas and returns a score out of 100. (BrandJet)
Treat that score as a copy diagnostic, not a prediction of inbox placement or open rate.
Your next step depends on the question you are trying to answer:
| Question | Best next step |
|---|---|
| Is my subject line clear and well structured? | Use the subject line tester |
| Does the full email contain risky wording? | Use the email spam word checker |
| Is my sending domain configured correctly? | Use the email deliverability checker |
| Which of two good subjects performs better? | Run an A/B test |
| Which testing product should I choose? | Compare the best email subject line testers |
BrandJet currently analyzes seven areas:
The public tool returns an overall score and currently documents these rating bands: (BrandJet)
| Score | Rating |
|---|---|
| 90+ | Excellent |
| 70 to 89 | Good |
| 50 to 69 | Needs Work |
| Below 50 | Poor |
A score of 90 does not mean a 90% open probability. It also does not mean Gmail has a 90% chance of placing the message in the inbox.
The number summarizes BrandJet's subject-line checks. It does not directly measure authentication, sender reputation, complaint history, recipient engagement, the email body, or mailbox-provider filtering.
Use the score to find weaknesses worth reviewing. Do not rewrite a truthful, relevant subject just to make the number higher.
A useful rule is:
Change a flagged element only when the change also improves clarity, relevance, accuracy, or readability for the recipient.
Length is mainly a readability and scanning consideration.
A very short subject can lack context:
Quick question
A slightly longer version can be more useful:
Acme onboarding benchmark
Long subjects can also bury the important idea.
Mailchimp recommends no more than nine words and 60 characters in its own subject-line guidance. That is a best-practice recommendation, not a universal Gmail display rule. (Mailchimp)
The better principle is to put the most important information early.
A subject checker can flag wording patterns worth reviewing, but a flagged word does not prove that Gmail has a universal banned-word rule for that term.
Consider:
Free migration included
If the migration really is free, removing the word solely to satisfy a scoring system may make the subject less accurate.
Instead, ask:
Google's sender guidance covers authentication, complaint levels, message formatting, reputation, infrastructure, and other factors. It does not reduce spam placement to a simple prohibited-word list. (Google)
Strong emotional wording can attract attention, but stronger language is not automatically better.
Compare:
Revolutionary solution for explosive growth
with:
Acme pipeline benchmark
For a B2B recipient, the second may be more credible because it describes the actual context.
Use power-word feedback as a prompt to review tone, not as an instruction to add hype.
BrandJet documents personalization as one of its subject-line checks. Its tool
also supports examples with variables such as {firstName} and
{company}. (BrandJet)
Personalization is useful when it adds genuine context.
John, quick question
uses a name.
Acme onboarding benchmark
may be more informative because it tells the recipient what the message concerns.
Personalization should explain why the message is relevant, not simply prove that a variable can be inserted.
An emoji can add visual emphasis, but it should not carry essential meaning.
Mailchimp notes that emojis can render differently across operating systems and recommends using them to supplement words rather than replace them. (Mailchimp)
A simple test works well:
If the subject stops making sense when the emoji disappears, rewrite the wording.
A strong subject should be understandable on the first scan.
Instead of:
Quick follow-up regarding a potentially useful opportunity for your sales
team
a more direct subject might be:
Acme pipeline gaps
provided that accurately describes the email.
Remove unnecessary qualifiers, filler, repeated punctuation, and vague language before trying to make the subject more clever.
Questions can work when the recipient immediately understands the topic.
Quick question?
offers almost no information.
Hiring SDRs this quarter?
gives the recipient context.
Use a question when a genuine question is the clearest framing, not because question marks are assumed to improve performance.
No.
A subject line tester evaluates subject copy. Gmail and other mailbox providers evaluate a much broader delivery system.
Google's current sender guidance covers SPF, DKIM, DMARC requirements for applicable senders, DNS configuration, TLS, message formatting, complaint behavior, and other sender-quality signals. Google also states that authentication helps receiving systems verify that messages are legitimate. (Google)
Yahoo similarly publishes authentication, complaint-rate, and unsubscribe requirements for applicable senders. (Yahoo Sender Hub)
It is more useful to think of deliverability as six layers:
A subject line tester mainly helps with the first layer.
If your subject looks healthy but delivery remains poor, stop making random wording changes and investigate the sending setup instead. BrandJet's email deliverability checker addresses domain and authentication checks, while its guide on how to improve cold email deliverability covers the broader process.
Use subject length as a mobile-readability heuristic, not as a universal truncation rule.
BrandJet's current tool shows character and word counts and includes a mobile-fit indicator. (BrandJet)
The practical goal is to make the important information visible early.
Compare:
A quick question about something we noticed in Acme's onboarding
process
with:
Acme onboarding question
The shorter version protects the core idea better if the inbox view cuts off later words.
Mobile inbox width varies by device, mail client, font size, sender-name length, preview-text settings, and interface design.
That means there is no single safe character limit that guarantees identical display everywhere.
Instead:
The objective is not simply "shorter." It is meaningful information earlier.
Use a simple revision workflow.
Start with the actual reason for the email.
Avoid fake urgency, false reply prefixes, or curiosity that the message body cannot support.
Review the overall score and each category separately.
One weak diagnostic does not necessarily require a full rewrite.
Prioritize issues in this order:
If a subject is clear and truthful, do not make it worse merely to satisfy a secondary scoring signal.
Changing one element at a time helps you understand what improved the diagnostic.
For example:
Wanted to share an idea with you
could become:
Acme renewal workflow
if the email actually concerns that workflow.
Run the revised subject through the checker again.
The workflow should be:
Draft -> Test -> Review -> Change one meaningful element ->
Retest
not:
Draft -> Change random words until the score reaches 100
A subject does not need a perfect score.
Stop when it is truthful, clear, relevant, readable, and appropriate for the recipient.
If you still have two credible versions, move to audience testing rather than continuing to optimize a heuristic score.
Use a subject-line tester to identify obvious weaknesses. Use an A/B test when you have two plausible variants and need evidence from your actual audience.
A checker answers:
Does this subject contain patterns worth reviewing?
An A/B test asks:
Did recipients respond differently to variant A and variant B under similar conditions?
Mailchimp likewise recommends testing subject lines with real audiences rather than assuming general best practices will produce the same result for every list. (Mailchimp)
When testing subjects, keep the other major variables as consistent as practical:
| Keep constant | Change |
|---|---|
| Audience selection | Subject line |
| Sender identity | |
| Email body | |
| Offer | |
| Links | |
| Sending window |
Choose the outcome that matches the campaign goal.
For a newsletter, opens or clicks may matter. For outbound sales, replies or qualified responses may be more meaningful.
Open-rate data also requires caution. Mailchimp notes that image loading, privacy protections, and automated activity can distort open tracking. (Mailchimp)
For a simple comparison, relative lift can be expressed as:
Relative lift = (Variant B rate - Variant A rate) / Variant A rate x
100
That calculation alone does not prove statistical significance. Sample size, randomization, audience mix, tracking quality, and the chosen success metric still matter.
Use the score to create a hypothesis. Use testing to evaluate it.
It reviews observable characteristics such as length, readability, question format, personalization, emoji use, and potentially risky wording. The result is a heuristic review of the subject line, not a prediction of inbox placement or campaign performance.
No. Inbox placement also depends on sender reputation, authentication, sending behavior, recipient engagement, message content, and mailbox-provider filtering. Use a subject tester for copy review and a separate deliverability check for domain and authentication problems.
There is no universal winning length. Keep the main idea visible on a mobile screen, remove words that do not help the recipient, and test the complete subject in context rather than optimizing for one character target.
No. A perfect heuristic score can still produce a vague, misleading, or irrelevant subject. Stop optimizing when the subject is truthful, clear, relevant, readable, and suitable for the intended recipient.
Run an A/B test when you have two credible variants and enough comparable recipients to learn from their behavior. Keep the audience, sender, message, offer, links, and sending window as consistent as practical so the subject line is the main changed variable.
Choose the tool based on the layer you need to inspect.
| What you need to know | Tool |
|---|---|
| Is the subject clear and well structured? | Email Subject Line Tester |
| Does the subject plus body contain risky copy patterns? | Email Spam Word Checker |
| Are authentication or domain issues affecting sending health? | Email Deliverability Checker |
| Which subject-line product fits my workflow? | Best email subject line testers |
| I need a starting email draft too | Free cold email generator |
BrandJet's spam word checker accepts an optional subject plus the email body and reviews configured copy patterns across the larger message. That makes it broader than the subject-line tester, but it still does not guarantee inbox placement. (BrandJet)
BrandJet's deliverability checker addresses a different problem. Its current public page documents checks including SPF, DKIM, DMARC, MX, reverse DNS, BIMI, MTA-STS, TLS-RPT, and blacklist status. (BrandJet)
For most lean B2B teams, the practical sequence is:
The goal is not a perfect score. The goal is a subject line that is clear, relevant, credible, and ready for a real recipient.