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Email Subject Line Tester for outreach emails

Paste up to 10 subject lines. See how each one is cut off on a phone, which words read as a mass mailing, and what to fix before you pitch an editor.

Test variations side by side. The best-scoring line is listed first.
Adds a check for whether each line mentions something specific to the person you are pitching.
Runs in your browser. Nothing you type is sent to us.

Why outreach subject lines are different

Most subject line advice is written for newsletters, where the reader already knows the sender and the goal is a slightly higher open rate across thousands of people. Outreach is the opposite. You are a stranger writing to one editor, blogger or journalist who gets pitches every day, and who decides in a second or two whether yours looks like a person writing to them or a template sent to five hundred sites.

That changes what a good subject line is. Clever wording and urgency help a newsletter; in a cold pitch they are the signals of a mass mailing. What works is short, plain and specific: something that could only have been written to this person, about their site.

What this tester checks

Length and the mobile cut-off

Phone inboxes often show only the first 30 to 40 characters of a subject, and desktop clients show more, depending on the app and window size. The tester shows each line cut at roughly those widths so you can see what the reader will actually see. Lines between about 20 and 55 characters score best. If yours is longer, move the specific part to the front.

Spam-style wording

Words like “free”, “guaranteed”, “act now” or “limited time” are flagged. On their own they rarely decide whether a message lands in spam. Sender reputation, SPF, DKIM and DMARC authentication, and how recipients react matter far more to filters. They are flagged because a human reads them as marketing, and a pitch that looks like marketing gets skipped.

Capitals, punctuation and emoji

Words in capitals, exclamation marks, repeated question marks, dollar signs and emoji all read as promotional in a one-to-one email. Common acronyms such as SEO, PR or AI are not counted as shouting.

Fake Re: and Fwd: prefixes

Starting a first email with “Re:” or “Fwd:” pretends there was an earlier conversation. It may earn an open, but it spends the reader's trust before they reach your first sentence, and the CAN-SPAM Act prohibits subject lines that mislead about a commercial message. The tester fails any line that starts this way.

Unfilled placeholders

Nothing ends a pitch faster than “Loved your post, [First Name]”. Square or angle brackets fail the check. Merge tags such as {{first_name}} get a warning, so you remember to confirm your sending tool fills them for every contact.

Overused pitch phrases

“Quick question”, “collaboration opportunity”, “guest post opportunity” and “link exchange” appear in so many templated pitches that many editors filter them by eye. They are warnings, not failures, because context matters, but a specific line almost always beats them.

Specificity

If you enter the site or article topic, the tester checks whether each line mentions it. It is the single most useful habit in outreach: a subject that names their article, their topic or a gap in their content tells the editor this email was written for them.

Weak and stronger examples

Guest post pitch. “Guest Post Opportunity!!” tells the editor nothing and reads as a template. “3 topic ideas for your budgeting section” names their site's content and promises something concrete.

Broken link or resource page. “Quick question” is vague. “Dead link on your home-office resources page” says what you found and where.

Digital PR. “EXCLUSIVE data you won't believe” is hype. “Data: rent rose fastest in 12 Midwest cities” gives a journalist the story in the subject line.

Follow-up. Send it as a reply in the same thread, so the original subject is kept and “Re:” is honest. Changing the subject to “Just following up” adds nothing.

How to use the results

Write three or four versions of the subject line for your campaign, paste them together, and fix every red check first. Then choose between the remaining lines on relevance, not on a few points of score. If you send enough pitches to measure, split a campaign between two lines and compare replies rather than opens; open tracking is unreliable now that some mail apps load images automatically.

A good subject line only earns a read. The email still has to be short, specific and useful. The email outreach guide covers the full pitch and follow-ups, the outreach email templates give you starting points to personalise, and the Guest Post Finder helps you build the list to send to.

FAQ

Subject line tester,
answered

No. The score counts known pitfalls: length, spam-style wording, capitals, misleading prefixes and unfilled placeholders. A line with none of them can still be ignored if the pitch is not relevant to the reader. Use the score to remove obvious problems, then judge relevance yourself.
Short enough to be read in full on a phone. Mobile inboxes often show only the first 30 to 40 characters, depending on the app and screen, so this tool treats 20 to 55 characters as the comfortable range and puts the specific part first.
Rarely on their own. Modern filters weigh sender reputation, authentication (SPF, DKIM and DMARC), sending volume and how recipients react far more than single words. Spam-style wording still hurts, because a human editor reads it as a mass mailing and skips it.
No. It implies an existing conversation that never happened. Recipients notice, it damages trust at the first touch, and the CAN-SPAM Act prohibits subject lines that mislead about the content of a commercial message. Use Re: only when you are genuinely replying in the same thread.
Yes. It runs in your browser, there is no sign-up, and nothing you type is sent to us. MRK Outreach, the paid product, handles the rest of the job: contacts, sending from your own mailbox, follow-ups and reply tracking.