---
title: "Email Subject Line Tester for Cold Email (Free) | Prosyo"
description: "Free subject line tester: score a cold email subject on length, tone and spam risk, and preview it in desktop and phone inboxes before you send."
url: "https://prosyo.com/tools/subject-line-tester/"
image: "https://prosyo.com/wp-content/uploads/2026/10/cropped-Prosyo-Icon-Transparent-1.png"
language: "en"
---

Free Tools

# Email Subject Line Tester

Score a subject line for length, tone and spam risk, and preview it in desktop and mobile inboxes.

Email Subject Line Tester Instant · free

## What is an email subject line tester?

An email subject line tester scores a subject line before you send it and shows how it will look in the inbox. The subject line is the only part of a cold email most people read before deciding whether to open, ignore or delete it, so small changes make a large difference.

This free subject line tester is built for **cold email**, not newsletters. It scores your subject out of 100 using cold outreach best practice: length in characters and words, spam-trigger words, ALL CAPS, exclamation marks and salesy symbols, emoji, fake “Re:” and “Fwd:” prefixes, and personalisation. It also previews the subject and your preview text in a desktop inbox row and a phone inbox, cut off exactly where inboxes usually cut them.

## Key takeaways

- Keep cold subject lines to two to six words, about 20 to 45 characters.
- Plain and specific beats clever.
- Never use fake “Re:” or “Fwd:”, caps, emoji or exclamation marks in cold email.
- Use your preview text as a second subject line.
- Judge subject lines by replies, not opens.

## How to use the subject line tester

1. **Type your subject line.** Include merge fields such as `{{company}}` or `{{first_name}}` if you use them.
2. **Add your preview text** (optional): the first line of the email, which most inboxes show after the subject.
3. **Press “Test subject line”.** You get a score, a grade, an inbox preview and a list of checks.
4. **Try three or four versions** and keep the strongest. Changing one word often moves the score.

## What makes a good cold email subject line

### Short: two to six words

Cold subjects that perform tend to be short and plain, between about 20 and 45 characters. Phones show roughly 35 to 40 characters of a subject before cutting it off, and long subjects read like marketing. The tester flags anything over 45 characters as a little long and over 60 as too long.

### Plain, not clever

Cold email competes with messages from colleagues and customers. Subjects that look like something a colleague might send, such as “question about hiring” or “idea for acme”, get opened because they look like real correspondence. Clever, punny or salesy subjects look like campaigns.

### Relevant to them

The strongest subjects reference the reader’s world: their company, role, a recent event or a problem they likely have. Merge fields such as `{{company}}` help when they produce something natural.

### Honest about the email

The subject should match what the email is about. Subjects that trick people into opening, such as fake “Re:” prefixes or false urgency, might lift opens once and then destroy trust, replies and your sender reputation.

## How the score works

| Check | What earns points | What loses points |
| --- | --- | --- |
| Length | 8 to 45 characters | Over 45 (a little), over 60 (a lot), under 8 |
| Words | Up to about 7 | More than 9 |
| Capitals | Normal or lower case | Whole words in CAPS (acronyms excepted) |
| Punctuation | Plain | Exclamation marks, “??”, “$”, “% off” |
| Deception | Honest | Fake “Re:” or “Fwd:” |
| Emoji | None | Any emoji (fine for newsletters, not for cold email) |
| Spam words | None | Each trigger word, such as free, guaranteed or act now |
| Personalisation | Noted as a plus | Not required |

The score is guidance based on what consistently works in cold outreach, not a prediction of your open rate. Open rates also depend on your sender name, your domain’s reputation and how well your list fits your offer.

## 25 cold email subject line patterns

Use these as starting points and make them specific. Replace the placeholders with real details.

- `question about {{company}}`
- `idea for {{company}}`
- `{{first_name}}, quick question`
- `your post on [topic]`
- `[mutual connection] suggested I reach out` (only when true)
- `hiring [role]?`
- `[their product] + [your category]`
- `congrats on [event]`
- `[problem] at {{company}}`
- `thoughts on [their initiative]`
- `for {{company}}'s sales team`
- `[competitor or peer] does this` (only with real knowledge)
- `before your next [event or quarter]`
- `a different take on [topic]`
- `[number] meetings, no new hires` (only with a real basis)
- `re-thinking [process]`
- `your [tool or process] setup`
- `quick idea`
- `worth a look?`
- `[city] [industry] teams`
- `[their goal] this quarter`
- `saw your job post`
- `[podcast or talk] you gave`
- `one question, {{first_name}}`
- `should I close the loop?` (for a final follow-up)

For tailored ideas from your offer and audience, use the AI [Subject Line Generator](https://prosyo.com/tools/email-subject-generator/), then test the best ones here.

## Preview text: the second subject line

Most inboxes show the first line of your email right after the subject. That preview text is your second chance to earn the open. Two common mistakes waste it:

- Opening with “Hi Jane, I hope this email finds you well”, which says nothing.
- Opening with your name or company: “My name is… and I work at…”.

Instead, let the first line continue the subject: subject “question about hiring”, first line “Saw Acme is hiring two SDRs this quarter…”. Add your first line in the preview field above to see them together.

## Lower case, title case or sentence case?

All three work. Lower case (“idea for acme”) is very common in cold email because it looks like a quick note between people. Title Case (“Idea For Acme”) looks more like a campaign. Sentence case is a safe middle ground. Whatever you choose, keep it consistent within a sequence, and never use ALL CAPS.

## Subject lines for follow-ups

Most cold sequences reply in the same thread, so follow-ups keep the original subject automatically, which is genuine and fine. If you start a new thread for a later step, use a new honest subject that adds a new angle, for example “different idea” or “last one from me”. Avoid fake “Re:” on a first email; recipients notice, and many filters do too.

## Testing subject lines properly

A tester helps you avoid obvious mistakes, but real results come from your own sends. If your volume allows, split-test two subjects on the same audience and the same body, change only the subject, and judge by **replies**, not opens. Open tracking has become unreliable because Apple Mail and some corporate gateways open messages automatically, and an open you cannot trust is not a good metric. Run each test on a few hundred sends before deciding.

## Subject lines by situation

The best subject line depends on why you are writing. These are patterns that fit common outbound situations, with an example of each.

| Situation | Pattern | Example |
| --- | --- | --- |
| They posted something relevant | Reference the post | your post on sdr ramp time |
| They are hiring | Name the role | hiring two sdrs? |
| They raised money | Congratulate briefly | congrats on the series a |
| They launched a product | Name it | acme insights launch |
| You share a connection | Name them (only with permission) | sam lee suggested I write |
| Common problem in their role | Name the problem plainly | reply handling at acme |
| Event or deadline they face | Tie to the moment | before q4 planning |
| Final follow-up | Close the loop honestly | should I close this out? |

## Ten subject lines that hurt cold email, and better versions

| Avoid | Why | Try instead |
| --- | --- | --- |
| Re: our conversation | Fake reply; there was no conversation | question about acme’s outbound |
| Quick question!!! | Exclamation marks look promotional | quick question, priya |
| Partnership opportunity | Vague and overused | idea for acme’s sales team |
| Increase your sales by 300% | Unbelievable claim, spam words | more first meetings from linkedin |
| FREE demo for Acme | Caps and “free” | worth a short look? |
| Following up | Says nothing new | a different angle |
| Can we hop on a call? | Asks for time before giving a reason | hiring sdrs this quarter? |
| Introduction | No reason to open | your post on sdr ramp time |
| The #1 AI platform for sales teams | Reads like an ad | for acme’s sales team |
| Don’t miss out | Manufactured urgency | before your q4 planning |

## Does the sender name matter more than the subject?

Often, yes. People decide whether to open based on who an email is from as much as what it says. A real person’s name (“Sam Lee”) outperforms a company name or a generic sender (“Acme Sales Team”) for cold outreach, because it looks like a person writing to a person. Make sure every sending inbox uses a real first and last name, and consider adding a profile photo so the sender looks human in Gmail and Outlook.

## Personalisation tokens done right

Merge fields are powerful when the data behind them is clean and dangerous when it is not. Before sending, check:

- **No blanks.** A missing company name produces “question about ” with nothing after it.
- **Natural capitalisation.** “ACME CORPORATION LTD” from a database reads badly; tidy company names to how people say them (“Acme”).
- **Short company names.** Remove “Inc.”, “Ltd”, “GmbH” and similar suffixes in subject lines.
- **Real first names.** Watch for initials, titles or full names in the first-name field.
- **Fallbacks.** Set a fallback for every token, or remove prospects with missing data.

## Example subject lines by audience

| Audience | Examples |
| --- | --- |
| SaaS founders | founder-led sales at {{company}} · your post on pipeline · after the seed round |
| Heads of sales | sdr ramp time · reply handling at {{company}} · q4 pipeline gap |
| Marketing leaders | outbound + your content · {{company}}’s webinar list · abm accounts |
| Agency owners | client reporting at {{company}} · new retainers in q4 · outbound for clients |
| Recruiters | [role] at {{company}} · hiring plan this quarter · senior [role] pipeline |
| Local businesses | {{company}} in [city] · weekday bookings · your google reviews |

## How inboxes cut off subject lines

Desktop inboxes show roughly 60 to 80 characters of subject plus preview text on one line, depending on screen width. Phones show the subject on its own line and cut it at roughly 35 to 40 characters, then show one or two lines of preview text below. That is why the preview in the tester shows both views, and why the most important words should come first: “hiring sdrs at acme?” survives truncation better than “quick question about whether acme is hiring sdrs”.

## Glossary

- **Subject line**: the title of the email shown in the inbox list.
- **Preview text (preheader)**: the first line of the email, shown after or below the subject.
- **Merge field**: a placeholder such as {{first_name}} filled per recipient.
- **Open rate**: the share of recipients recorded as opening; increasingly unreliable because of automatic opens.
- **Reply rate**: the share of recipients who reply; the metric to judge cold subject lines by.

## Worked example: improving one subject line

Start: **“Increase Your Sales Pipeline By 300% With Our AI Platform!”**. The tester scores it in the 20s: 57 characters, nine words, title case that reads like an advert, an exclamation mark, and “increase sales”-style wording. Version two: **“more pipeline for acme’s sales team”**, around 35 characters, no spam words, scores in the 80s. Version three: **“sdr hiring at acme”** (written because Acme is hiring SDRs), under 20 characters, specific and honest, scores in the 90s and, more importantly, gives Priya a real reason to open. The best subject came from research, not wordsmithing.

## How Prosyo helps

Prosyo writes each first message, subject included, from what the prospect actually posted or did, so subjects reference something real. It runs LinkedIn and email together, stops on reply and reports replies and meetings, not just opens. [Try it free for 7 days](https://prosyo.com/pricing/).

## Related free tools

These tools are often used together with the Subject Line Tester. All of them are free, and the checkers and calculators run instantly in your browser.

- [Subject Line Generator](https://prosyo.com/tools/email-subject-generator/): Twelve short, honest subject line ideas from your offer and audience, written by AI.
- [Cold Email Grader](https://prosyo.com/tools/cold-email-grader/): Grade a cold email on length, readability, reader focus, links, call to action and spam risk.
- [Spam Word Checker](https://prosyo.com/tools/spam-word-checker/): Highlight every spam-trigger word in your email by category, with plainer alternatives.
- [Cold Email Generator](https://prosyo.com/tools/cold-email-generator/): Get three short, specific cold emails with subject lines, written by AI from your offer and audience.

## Frequently asked questions

### How long should a cold email subject line be?

Two to six words, or roughly 20 to 45 characters. Phones cut subjects off at about 35 to 40 characters, and short, plain subjects look like real correspondence.

### Should I use the recipient’s name in the subject line?

It can help when it reads naturally, as in “Jane, quick question”. The company name is often just as effective and less overused. Make sure merge fields never produce blanks or odd capitalisation.

### Are emoji good in cold email subject lines?

Generally no. They make a message look like a newsletter or promotion. Keep cold subjects plain.

### Is it OK to use “Re:” in a cold email subject?

Not on a first email. Pretending a message is a reply breaks trust the moment it is opened and is flagged by some filters. Only use Re: when you are genuinely replying in a thread.

### How do I test which subject line works best?

Score your options here to remove weak ones, then split-test the best two on the same audience with the same email body, and compare replies rather than opens.

### Do subject lines with questions work better?

Sometimes. A question works when the answer matters to the reader, as in hiring SDRs this quarter?. Generic questions such as Can we talk? rarely do. Test a question and a statement version on the same audience.

### Should every email in a sequence have a new subject line?

Not usually. Follow-ups sent as replies in the same thread keep the original subject, which is natural. Use a new honest subject only when you start a new thread with a new angle.

### Does the subject line affect deliverability?

It can. Spam-style wording, caps and symbols in the subject are scored by some filters, and subjects that mislead lead to deletions and spam reports, which hurt your reputation over time.

### Is this subject line tester free?

Yes, with no sign-up. It runs in your browser and stores nothing.

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