Email subject line tester

Review your subject line before sending. Check length, emphasis, spacing and personalization variables, then use your audience and purpose to prepare three editable text templates.

Check an email subject line

Free, browser-local writing checks. No account, email sending or open-rate prediction. Promotional-word checks use English phrases; word counts use whitespace.

Add an audience and a short, accurate purpose to get three editable text templates using your words.

What does an email subject line tester check?

This local tool checks character count, predominantly uppercase text, repeated question or exclamation marks, common personalization markers, spacing and a small list of promotional phrases. Each result explains the rule so you can decide whether it matters for your message.

It does not inspect an inbox, authenticate your sending domain, contact recipients or predict engagement. Inbox placement depends on many factors beyond subject text. The optional templates simply reuse your words; richer AI rewriting is available as a separate task in Okou.

Your wording → transparent checks → editable drafts → real campaign test

How to check an email subject line

Start with the subject itself; add context when you want text templates.

  1. 01

    Paste your subject

    Enter up to 500 characters. Add an audience and a short, accurate purpose or offer if you want three template variations.

  2. 02

    Review the checks

    Read the explanations and the illustrative inbox preview. Confirm every claim and personalization fallback against the actual email.

  3. 03

    Edit and copy

    Edit the direct, audience-first and purpose-first templates. Copy a draft into your email platform, preview real recipients and test appropriate variants.

What emails can you review?

Use the checks as writing assistance across common business emails.

  • Newsletters

    Make the main topic visible early and keep the subject consistent with the editorial content.

  • Sales follow-ups

    Check emphasis and placeholders while keeping the relationship and next step accurate.

  • Customer updates

    Review launch, event and service updates without unsupported urgency or promises.

How can subject checks improve a newsletter workflow?

Develop the newsletter content and subject together so the inbox promise matches what readers find inside.

Explore the AI newsletter generator
How can subject checks improve a newsletter workflow?

Rewrite a subject with the full email context

Help me improve the email subject line and email body I provide. Ask about the audience and intended action, then draft three distinct subject lines that accurately represent the email. Explain the tradeoffs and suggest an A/B test. Do not invent discounts, urgency, claims or predicted open rates, and do not send email.
Draft subjects in Okou

The checks above are free and local. This optional AI writing task opens Okou after sign-in and uses credits. Paste the subject and email context there; local input is not sent automatically.

Get better results with connectors

Bring your draft, audience and intended action to Okou for context-aware subject options and an experiment brief.

Useful connectors

  • Gmail
  • Google Docs
  • HubSpot

Give the subject the full email context

Develop the newsletter content and subject together so the inbox promise matches what readers find inside.

Review my email draftBrowse workflow examples

Email subject line tester FAQs

Is the email subject line tester free?

Yes. The local checks, editable templates and copy buttons work without an account. The separate AI writing task in Okou requires sign-in and uses credits.

Does it predict open rates or assign a spam score?

No. Subject text alone cannot establish opens or inbox placement. The checks are transparent writing rules, and promotional phrases are context prompts rather than a spam verdict.

Are the three alternatives AI-generated?

No. The direct template normalizes spacing and repeated punctuation. The other two prefix your supplied audience or purpose. Edit them to fit the message, or use the optional Okou task for contextual AI rewriting.

How accurate is the inbox preview?

It shows the first 45 Unicode code points as an illustration. Actual display depends on the email app, font, sender name and screen width. Combined emoji can contain more than one code point.

Does the page upload my subject or send email?

No. Local analysis stays in your browser and does not send messages. If you choose the optional Okou writing task, paste your subject and context there yourself.

Which languages are supported?

Length, spacing and punctuation checks work with many scripts. Promotional-phrase checks use a small English phrase list, and word counts use whitespace. The interface and draft labels follow the selected page language. Have a fluent reader review non-English subjects.

Okou also has the AI newsletter generator, the AI follow-up email generator and the contact list cleaner.

Give the subject the full email context

Bring your draft, audience and intended action to Okou for context-aware subject options and an experiment brief.

Review my email draft