10 best free subject line generators to boost your open rates

Around 47%—that’s the amount of email recipients who open messages based on the subject line. Not what you expect to see after perfecting your email campaigns for days, right? Email has become a more competitive channel, and going the extra mile is the new reality.

So, how do you grab attention in such a competitive environment? Most importantly, how do you never run out of ideas? 

What is an email subject line generator?

A subject line generator is an AI-based tool that can optimize or create unique subject lines depending on your input. Are you looking for lines with a question mark or those with a number? What about spicing them up with emojis?

Either way, subject line generators are the right answer. These tools generate ideas in seconds, ensuring you never face a writer’s block.

Benefits of subject line generators

What about the subject line generators’ value? Let’s review how email specialists can benefit from these tools, aside from saving time. Here are four main perks:

• emotional appeal implementation: Elements of urgency, curiosity, or FOMO let professionals create attention-grabbing subject lines that evoke different emotions;
• localization: Some tools generate subject lines in various languages depending on the settings. This means you speak the same language as your target audience and minimize misunderstandings;
• time-saving: Even a short text element, such as a subject line, requires time and coming up with more variants becomes more challenging with every take. Subject line generators provide multiple ideas in a matter of seconds;
• enhanced creativity: Generators can become your never-ending source of subject line ideas, fueling creativity. You can experiment with structure, tone of voice, and emojis on the spot.

Recent subject line generators consider various factors to keep emails at the top of inboxes and minds, and boost open rates by up to 10%. This not only improves your work, but also impacts your campaign’s results.

10 best tools to generate subject lines

Looking for the best subject line generators takes time that professionals rarely have. I get it. That’s why Stripo’s team has picked the 10 best Google ranking tools to ease creation. 

1. Stripo AI subject line generator 

Stripo AI subject line generator is the find for those who value quality, convenience, control over the process, and speed. Would you like to establish authority or commitment? How about adding validation or social proof? Stripo AI subject line generator adjusts the tone to your needs. Here is what it brings to the table:

• quantity of variants: The tool delivers six options;
• style: Tone of voice varies from company to company, so our generator can adjust to yours;
• emojis: You can add emojis to find the perfect subject line that wins people over. You need not be formal;
• writing cases: Stripo AI subject line generator supports different cases: sentence; title; or random case;
• languages: Our team has ensured that the tool speaks the same language as your audience and can generate catchy subject lines for any occasion.

You may preview, copy, and perfect the best-fitting option by clicking the “Improve” button. Furthermore, a character counter will help you fit within limits, so your email subject never gets cut off.

2. Encharge

Are you tired of the spammy results that some email subject line generators create? Encharge gets it. That’s why they created an AI email subject line generator based on Open AI technology and adjusted it to work with ChatGPT-4o. This tool will crawl the Internet and generate email subject line templates approximated to human speech. Here is what it has to offer:

• quantity of variants: Clicking on the “Generate AI Subject Lines” is enough to produce seven variants;
• style: You can pick the tone of voice from the drop-down list to ensure it matches your company’s guidelines;
• personalization and context: There’s an option to describe the email and enter company details to create personalized subject lines.

The Encharge subject line generator is intuitive and precise, which is a good pick for those who value simplicity.

3. Keap 

Keap subject line generator promises to produce ideas that will get your marketing messages more opens, but what features does it offer? Let’s take a look:

• quantity of variants: You get the five email subject lines that can help increase open rates;
• message type: Newsletter, re-engagement, follow-up, promotion, resources, or registration—you can pick any variant;
• target audience and industry: You can choose a target audience and industry so that the generator can tailor your subject line accordingly;
• interests and keywords: If there’s a need to link the subject to the keyword or particular interest, you can enter the details during the last step.

Just like that, you receive subject lines adjusted to the audience or industry and get results emailed to you.

4. SalesBlink

How about creating cold email subject lines? SalesBlink offers a free subject line generator to get more people to open your message. I suggest that we study the main differences:

• quantity of variants: You get five fresh email subject line ideas;
• product or service: The tool lets you add key details about your product or service;
• target company name: You may include a company name in the subject line to add more personalization elements. 

Next to each uniquely structured variant, there is an open rate that helps you navigate better. You can always generate more email subject lines or use them in cold emails using the platform’s services.

5. ActiveCampaign

What if you need a subject line that is aligned with keywords? Then ActiveCampaign’s subject line generator is the right choice for you. Here is what it offers:

• quantity of variants: The tool produces four unique options that could be the next best performers;
• keyword category: There are three options: benefit; topic; and pain point. Choose yours and continue;
• keyword: The last setting is the keyword. Once it is entered, the tool will create subject line ideas.

You can either generate more variants or copy the best one and, with a touch of personalization, create a genuinely great subject line.

6. Klaviyo

Precise and easy to use, the Klaviyo subject line generator is a great tool that bases output on the sphere and email details. Let’s review my testing results:

• quantity of variants: You get four different subject lines;
• industry: There are five industries for you to choose from: beauty; fashion; home & garden; CPG; restaurant & wellness;
• type of email: Product launch or product promotions are email types the generator supports;
• example prompt: You can insert a relevant example so that the results are tailored properly, then hit the “Generate” button.

As an output, the tool creates a list of subject lines with and without emojis, sentence and title case, or shorter and longer lines. Whatever option you pick is entirely up to you.

7. Copy.ai

Copy.ai offers a simple and convenient email subject line generator. The only thing separating you from the ideal output is a brief description. Here are the details on a way around this tool:

• quantity of variants: Copy.ai generates one subject line;
• description field: You can add a few details on the pain points to address, or the general topic/what the email is about, and the tool will handle the rest.

In seconds, you get an email subject line and a brief analysis of it: length, whether it has action verbs; personalization elements; and what emotions it evokes.

8. Headline Studio

What if a subject line alone is not enough, and you need supporting tips? Headline Studio’s subject line generator may do the trick. Let’s see how it differs from the rest:

• quantity of variants: Clicking on the button generates you four email subject line variants;
• topic: This tool requires a few words on the topic or keywords;
• target audience: You can enter details on the target audience so that the generator can adjust the subject line to the recipients better;
• tone of voice: Finally, you can enter your company's tone, which eliminates discrepancies between brand guidelines and generated results.

Each variant includes a brief analysis and provides suggestions for improvement. More results are available at the click of a button.

9. Salesforge

Alignment between a subject line and email copy is a must for any campaign’s success, and I have just the right tool. Salesforge offers a subject line generator that creates variants based on email content. Here are the details:

• quantity of variants: The generator creates a list of five email subject lines for you to experiment with;
• email body: Unlike other tools, Salesforge needs only the email body to craft subject lines.

You can generate more options or copy the existing list and adjust it to your needs. Having completely unrelated subjects and content is no longer a concern.

10. Mailberry

Not a fan of coming up with descriptions? Mailberry’s subject line generator is here to guide you. Instead of fields to fill in, this tool asks questions instead:

• quantity of variants: Mailberry creates a single subject line variant;
• questions: You are asked four questions about brand, company’s description, goal, and recipient’s benefit, then you can paste the email content into the line. 

Your input is the foundation of the subject lines you get. Once the details are clarified, the tool will provide a catchy subject line example. There’s always an option to generate more variants or start over.

Tips to improve your own email subject lines

Now that you know what tools will free you from writer’s block, we can discuss email subject line tips. What are three recommendations to try? Let’s have a look:

• leave curiosity gaps: Subject lines with slight information gaps can make email content more desirable by sparking curiosity and generating a sense of exploration;
• stick to the brand’s voice: Even a tiny element, such as a subject line, should match the company’s tone of voice. Whether your business prefers friendliness or formality, stick to the choice;
• personalize: Personalization goes beyond a first name and has recently has shifted to advanced variables. Woodpecker’s study found that cold email campaigns with advanced personalization reach 63% open rates, while non-personalized ones only get to 48%;
• keep them short: Subject lines with lengths of up to 70 characters have the highest open rates at 43.38%. Another study by Twilio indicates that the best results come from email subject lines that comprise only 2-4 words.

How to add a subject line to your email in Stripo

Stripo’s team has ensured that you can add subject lines easily without leaving the editor. Here are four steps you need to take:

1. Open any template you like.
2. Go to the “Message Settings” tab.
3. Enter your subject line into the dedicated field.
4. Improve with AI or add emojis if needed.

Aside from the subject lines, you also can add preheaders. This short text follows the subject line when an email is previewed and is perceived as its addition. In Stripo, you have two options: include the preheader text or add whitespace. What happens if you don’t include one? Let’s compare three emails from my inbox:

• variant 1: This email has a preheader, which is a logical continuation of the subject line;
  
  
• variant 2: This is Stripo’s email with whitespace instead of the preheader text. It’s an easy way to leave the field blank and avoid displaying the email body;
  
  
• variant 3: This message does not have a preheader or white space, so the recipient gets a spoiler of what’s inside instead. 
  
  

The preheader is a great idea to keep the subject line short while still sharing the idea with the subscriber. It makes it easy to hide the email text from showing and keep up the intrigue until the end.

Wrapping up

Always coming up with new email subject line ideas is a heavy burden, even for seasoned marketers. A solution? AI subject line generators that adjust to your tone, industry, and target audience, as well as consider how you prefer to input information. Whether you’d like to select options from the drop-down list, describe prompts in detail, use email copy, or answer questions, there’s a tool to match your needs.

I hope you find your next favorite subject line generator on this list. Good luck creating the best-performing lines!