Free cold email subject line analyzer.
Type a subject line and see how it survives three things in a row: a phone screen that truncates it, a filter that scores it, and a person deciding in about a second. The reference below covers every flag, and the one thing no subject line can fix.
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Cold subject lines at a glance
| Item | Value |
|---|---|
| Its one job | Earn the open without promising something the email does not deliver |
| Length | Five words or fewer, under about 35 characters, so it survives a phone |
| Case | Sentence case or lowercase. Title Case reads as marketing |
| What it cannot do | Save a weak angle. The subject gets the open; the angle gets the reply |
| Personalization tokens | Fine, but only where the underlying data is airtight |
What is a cold email subject line for?
A cold email subject line is a promise short enough to read in a list view, and its only job is to earn the open without lying about what is inside.
That framing rules out most of what people try. Curiosity gaps work until the email does not pay them off, at which point the open converts into a delete and sometimes a spam complaint, which costs more than the open was worth. Cleverness reads as marketing, and marketing is the category a cold email is trying not to be sorted into.
What survives is specificity, relevance or plain curiosity, in five words, cased like a colleague wrote it. And the honest caveat that should sit next to every subject line guide ever written: this is the smallest lever on the page. A great subject line on a weak angle produces opens and silence.
How to read your score
The analyzer scores the line and returns a verdict with the specific flags behind it.
Would pass internal review means nothing mechanical is working against you. The advice attached is still to test it against a second angle, because that is the only way to find out what a market answers.
Decent bones means the line is close and the flags below it are worth fixing before sending.
Working against you before the email is opened means something on the line is costing you the open outright: length that truncates badly, casing that reads as bulk, or phrasing filters treat as promotional.
Personalization tokens get their own note rather than a pass or fail, because they are only as good as the data behind them. A token that resolves to an empty string, or to a company name spelled the way a scraper found it, does more damage than no personalization at all.
What each flag means
| Flag | Why it matters | Fix |
|---|---|---|
| Too long | Truncates on a phone, often mid-phrase, changing what the line appears to say. | Cut to five words, front-loading what earns the open. |
| Title Case | Reads as a campaign rather than a message from a person. | Sentence case, or lowercase. |
| All caps | A genuine filter signal and a human one. | Remove entirely. There is no cold email case for it. |
| Exclamation marks | Stacked punctuation is scored by filters and read as hype by people. | Delete. A question mark is fine. |
| Promotional phrasing | Words associated with bulk marketing carry a small but real cost at the margin. | Say the same thing the way you would to a colleague. |
| Emoji | Marks the message as a campaign, which is the opposite of the impression you want. | Remove for cold outbound. |
| Personalization token | Only as reliable as the data behind it. A broken token is worse than none. | Keep only where the field is verified for every row. |
| Fake thread markers | Re: or Fwd: on a thread that never existed works once and costs the relationship. | Never use them. |
Patterns that hold up
| Pattern | Why it works | Fails when |
|---|---|---|
| Reference a real signal | Specific and current, so it reads as written for them. | The signal is older than a week or two. |
| Name the problem plainly | Self-selects the people who have it. | You guessed the problem wrong. |
| Ask a short, real question | Reads like a colleague, invites a reply rather than a click. | The question is rhetorical or obviously templated. |
| Two or three lowercase words | Looks like internal mail, which is what gets opened. | It is so vague it promises nothing. |
How to write and test a subject line
- Write the email first. A subject line written before the angle exists is a guess about a message you have not made yet.
- Pull the subject from the strongest line in the body. That way the open is paid off by the first sentence rather than contradicted by it.
- Cut it to five words. Then check where it truncates at phone width.
- Read it in sentence case, out loud. If it sounds like a campaign, it looks like one too.
- Test it against a genuinely different line, not a variant. Two phrasings of one idea teach you nothing.
- Judge it on replies, not opens. Open tracking costs deliverability and reports a number you cannot trust.
Common questions about cold email subject lines
How long should a cold subject line be?
Five words or fewer, and under about 35 characters so it survives a phone screen. Length is not what filters punish; truncation is what readers punish, and a subject cut in half rarely says what you meant.
Title case or sentence case?
Sentence case, or lowercase. Title Case On Every Word reads as marketing, and marketing is the category a cold email is trying not to be sorted into. Write it the way you would write it to a colleague you already know.
Do emojis and punctuation hurt?
Emojis mark the message as a campaign, which is the opposite of the impression you want. Question marks are fine. Capitals and stacked exclamation marks are a genuine filter signal as well as a human one.
Does using Re: or Fwd: to lift opens work?
It works exactly once, and it costs the reply. Faking a thread that never existed tells a buyer you will misrepresent other things too. The open converts into a delete, and sometimes into a spam complaint that costs more than the open was worth.
Should I put the company name in the subject?
Only where the data is clean for every row. A token that resolves to a scraped legal entity name, or to nothing at all, is more conspicuous than no personalization, because it tells the reader a system wrote this. Verified field, or leave it out.
How do I know if my subject line is the problem?
You usually do not, and that is the point. Opens are unmeasurable without a pixel that costs deliverability, so the subject line is the hardest element to attribute. Judge angles on interested replies and treat the subject as something to keep short and honest rather than something to optimize.