Cold Email Subject Line Grader
Subject lines decide whether a cold email is ever read. This free grader scores a subject line out of 100 and explains exactly what to fix: length, spam trigger words, formatting and personalization. Everything runs in your browser, so your copy is never uploaded or stored.
Free tool · nothing is uploaded
Grade your subject line
Checks length, spam triggers, formatting and personalization as you type, then tells you exactly what to fix.
- Length & truncation
- Spam triggers
- Personalization
- Clarity
Your subject line
Aim for 30–50 characters. Merge tags such as {{first_name}} are detected automatically.
Characters: 0 Ideal 30–50
- Characters 0
- Words 0
- Flagged terms 0
Used only to check whether the subject actually mentions that person or company.
Score
Type a subject line above to see your score, grade and fixes.
— Enter a subject line to see your score
Feedback
- Info Type a subject line above to run the checks.
Inbox preview
Amber = flagged word Red wavy = shouting Blue wavy = punctuation or emoji
Preview length and truncation vary by device, client and font size.
- 30 chars—
- 50 chars—
- 70 chars—
What is a cold email subject line grader?
A cold email subject line grader is a checking tool for the line of text that appears next to your message in someone’s inbox. It compares the subject against the handful of things that reliably affect whether recipients open it: how long it is, whether it contains commonly flagged promotional words, whether it is formatted sensibly, and whether it shows any sign of being written for that specific person.
It is a writing aid, not a crystal ball. No tool can predict opens, because inbox placement also depends on domain reputation, authentication, sending volume, engagement history and the reader’s context. What a grader can do is catch obvious problems before a stranger does.
How to use this subject line grader
- Type or paste the subject line you plan to send into the Subject line field.
- Optionally add the recipient’s first name or company in the second field. The tool then checks whether that name appears in the subject.
- Watch the score, the letter grade and the four category bars update as you type.
- Read the Feedback list. Items labelled Fix, Watch and Tip are the ones to act on.
- Check the Inbox preview and the 30, 50 and 70 character rows to see where your subject would be truncated.
- Edit, retype and compare scores. Use Copy subject when you are happy, Load sample to see worked examples, and Clear to start again.
How the score is calculated
The overall score is a weighted blend of four category scores, each from 0 to 100.
| Category | Weight | What it measures |
|---|---|---|
| Length | 30% | Character count (60% of the category) and word count (40%) |
| Spam safety | 30% | Promotional trigger words, all-caps words, repeated ! or ?, emoji, and “Re:” / “Fwd:” prefixes |
| Personalization | 25% | Merge tags such as {{first_name}}, and whether the recipient you entered appears in the subject |
| Clarity and specificity | 15% | A concrete element such as a number, a question, or direct address (“you”, “your”) |
The character bands are straightforward: 30–50 characters scores best, 20–29 and 51–60 score moderately, and anything under 20 or over 70 loses points quickly because it is either vague or gets cut off. Word count favours three to seven words.
Penalties are capped, so one repeated word cannot drive the score to zero. The final number is clamped to 0–100 and mapped to a grade: A (85+), B (70–84), C (55–69), D (40–54) and F (below 40).
What each check looks for
Subject length and truncation
Most mobile inboxes show roughly 30–50 characters of a subject, and desktop clients usually show more. The tool shows your subject cut at 30, 50 and 70 characters so you can see whether the important part survives.
Spam trigger words
The checker scans for a fixed list of classic promotional phrases such as “act now”, “guaranteed”, “limited time”, “100%” and “free”. These are writing signals, not a deliverability verdict. A legitimate word like “free” is not automatically harmful, and modern filters weigh many other signals. Treat a match as “a human might read this as promotional”, then decide.
Formatting
All-caps words of three letters or more, several exclamation or question marks, and emoji are flagged. None of these is fatal on its own, but they change how the line reads at a glance.
Personalization
If the subject contains a merge tag such as {{first_name}} or {{company}}, the tool recognises it. If you enter a recipient name or company, the tool checks whether that exact text appears in the subject.
Clarity and specificity
Subjects with a number, a question, or direct address tend to read as written for one person rather than sent to a list. This category simply rewards those signals.
Worked examples
| Subject line | Score | Grade | Main takeaway |
|---|---|---|---|
| Quick idea for {{company}}'s pipeline | 83 | B | Good length and personalization; add a specific detail such as a number or a question. |
| Sarah, 12 minutes to fix your follow-ups? | 90 | A | Mentions the recipient, includes a number and a question, and stays inside the ideal length. |
| Still booking demos by hand? | 72 | B | Reads well and asks a question, but is slightly short and has no personalization. |
| ACT NOW!! Increase sales 100% guaranteed!!! | 53 | D | Four trigger phrases, two all-caps words and five exclamation marks. |
These are outputs from the algorithm described above, not benchmarks from real campaigns.
Limitations and accuracy
- The score is a heuristic opinion based on the rules on this page. It is not a spam-filter score and does not predict open or reply rates.
- Trigger words are judged in isolation, so industry context and your brand voice are not considered.
- Personalization detection is literal. “Hi Sarah” will not match an entry of “Sarah Smith”, and a nickname will not match a legal name.
- Truncation depends on the recipient’s device, font size and email client. The 30/50/70 rows are illustrative, not guarantees.
- If a browser does not support the emoji-detection feature used internally, that single check is skipped; everything else still works.
Frequently asked questions
How long should a cold email subject line be?
A common working range is 30–50 characters, or roughly three to seven words. Short enough to survive mobile truncation, long enough to say something specific. This grader rewards that range but does not treat it as a rule you must obey.
Does this tool check deliverability?
No. It checks the writing of the subject line only. Inbox placement also depends on your sending domain, SPF/DKIM/DMARC setup, sending volume, list quality and engagement. A perfect subject line will not rescue a badly configured sending domain.
Will fixing the flagged words guarantee my email lands in the inbox?
No. Avoiding promotional language removes one avoidable risk signal. It does not guarantee placement, and no tool can promise that.
Is my subject line uploaded anywhere?
No. The tool is pure HTML, CSS and JavaScript running in your browser. There is no server request, no account, no cookie and no local storage. Nothing you type leaves the page.
Can I grade a whole sequence at once?
This page grades one subject line at a time. Paste each subject in turn to compare scores.
Does a high score mean I should send it?
A high score means the line avoids the obvious problems this checker looks for. It still has to be accurate, relevant and honest, and it should match the body of the email. Use the score as a sanity check, not a replacement for your own judgement.
Related tools
- Subject line generator — create variants to grade here
- Spam word checker — a deeper scan of promotional language
- Deliverability risk scanner — links, caps and attachments across a whole email
Next step
Working on an outreach system rather than a single email? That is what mizanursguide.com helps with. See how we build cold email campaigns that get replies instead of silence.