Skip to content
Get started

Newsletter check

Do4U checks a newsletter or marketing email before you send it. You paste the HTML or choose a saved .html or .eml file. The code counts the length of the subject and the preheader and shows guidance for phone and desktop, flags capital letters, many exclamation marks and words some spam filters weigh, looks for the unsubscribe link and sender details, finds images without alt text, compares text and images, measures the size of the HTML and lists every link with its text, tracking parameters and problems such as http or “click here”. With an .eml file it also checks the plain-text part and the List-Unsubscribe header. Then the AI suggests subject lines with a preheader and clearer wording. Do4U never opens your links and sends nothing.

Try it now Pricing

Who it is for

For shops, agencies, associations and small businesses that send newsletters themselves and want to catch mistakes before the send button, without a test send to many inboxes.

Typical uses

  • Check a newsletter before it goes out
  • Find images without alt text, http links and link texts like “click here”
  • Check the unsubscribe link and the List-Unsubscribe header in an .eml file
  • Get subject lines with a preheader that fit on a phone

Example

Input

HTML: <title>HUGE DISCOUNTS!!! Everything must go</title> <p>Hello! Our autumn sale starts today with many offers for you and your family.</p> <a href="http://shop.example.com/sale?utm_source=newsletter">Click here</a> <img src="hero.jpg">

Result

Style of the subject → check: words in capital letters, 3 exclamation marks Preheader → check: no own preheader, the inbox shows the first text Unsubscribe link → missing Alt text of images → check: 1 of 1 images has no alt attribute Links → check: http instead of https, link text says little Tracking parameters → utm_source The AI suggests subject lines with a preheader and clearer wording. The code counts every length and drops suggestions that are too long or contain a figure that is not in your email.

A fixed example, shortened. Real results are AI-generated: please check them.

Price and limits

Price
usually 1–3 credits
Available with
Free, With package
Input limit
Up to 300,000 characters per file

Privacy

Processed on our own servers in the EU (Poland). Inputs and results are deleted after 7 days (Free) or 30 days (packages), or right after you see the result if you choose not to store them. Images are deleted right after processing.

In the API

Tool name: newsletter_check. Create a job with POST /api/v1/jobs and fetch the result with GET /api/v1/jobs/{id}. You find your API key in your account.

curl -X POST https://do4u.eu/api/v1/jobs \
  -H "Authorization: Bearer d4u_…" -H "Content-Type: application/json" \
  -d '{"tool": "newsletter_check", "html": "<html>…</html>", "subject": "…"}'

Full API documentation →

Questions and answers

Does Do4U open my links or send the email?

No. Do4U reads only the HTML or .eml you give it. It never opens a link or loads an image, and it sends nothing. The link table shows the targets as plain text.

What does the code check and what does the AI do?

The code checks subject and preheader, the unsubscribe link, sender details, images, the size of the HTML and every link. The AI only suggests subject lines with a preheader and better wording. The code counts their length and drops suggestions that are too long or contain a figure that is not in your email.

Are the length limits fixed rules?

No. Where a subject is cut depends on the email app, the device and the font. Do4U shows guidance: on a phone often about 40 characters, on a desktop more. Put the important words first.

Is my text stored?

Only as long as needed: 7 days on Free, 30 days with a package – or not at all if you choose not to store it. Processing happens on our own servers in the EU (Poland).

Can I use the result right away?

Results are AI-generated. Please read them before you publish or send them.

Related tools

  • Headlines and subject lines

    Writes variants of headlines, subject lines and preheaders for pages, newsletters and ads. The length of every line is counted by code.

  • Proofreading

    Fixes spelling, grammar and punctuation in the language of your text and marks every change.

  • Alt texts

    Short image descriptions for screen readers and search engines.

All tools →