Free Email Subject Line Tester
Score your subject lines before you send — and see exactly why each point was deducted.
Your subject lines (one per line, up to 5)
Optional: email body (first lines — checked for spam phrases too)
Scores update as you type. Nothing you type is sent anywhere — the whole check runs in your browser.
Something not working?
Tell us what went wrong — it helps us fix the tool. Only what you type below is sent; your copy never leaves your device.
Need more power? Meet Subject Line Tester Pro
One-time payment. Yours forever. No subscription.
| Feature | Free | Pro |
|---|---|---|
| Subject lines per run | Up to 5 | Unlimited batch |
| Spam-phrase, length & tone checks | Yes | Yes |
| Phone & desktop inbox preview | Yes | Yes |
| Saved variant history | — | Yes |
| Custom spam-word list for your industry | — | Yes |
| Ads | Shown on page | Ad-free |
| Updates | — | Lifetime free updates |
Frequently asked questions
Is my copy sent to a server?
No. Scoring runs entirely in your browser against a bundled word list. Nothing you type is sent, stored or logged — you can verify this in your browser's network panel.
What makes a good subject line?
Short and specific wins: 30–50 characters, 3–7 words, no spam-trigger phrases, no ALL CAPS, no stacked exclamation marks, and a concrete detail (a number, a name, a date) beats a generic promise. The breakdown under each score shows exactly which of these your line passes or fails.
Does a high score guarantee my email lands in the inbox?
No — and any tool that claims otherwise is misleading you. The score only checks the words. Inbox placement also depends on your domain reputation, SPF / DKIM / DMARC setup, sending volume and how recipients have engaged with your mail before. Use this tester together with our Email DNS Checker.
Why do other testers give the same line different scores?
Because every tester uses its own secret word list and weights. This one shows its full rule breakdown — every point gained or lost, with the reason — so you can judge the advice instead of trusting a black-box number.
Should I use "Re:" in a first email?
No. Starting a first email with Re: or Fwd: pretends a conversation already exists. It can lift opens, but readers notice, reply less, and filters treat it as a spam pattern — misleading subjects are also against US CAN-SPAM rules.