Newsletter CTA Box Widget

Promote your newsletter anywhere on your site with a finished call-to-action box: headline, what readers get, how often it arrives, your privacy promise and an optional reader count. The Subscribe button opens your existing Substack, Mailchimp, Buttondown, Kit or other sign-up page - A2Z never collects an address.

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Theme
Auto follows the visitor's light/dark setting.
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Attribution on your page
Optional and entirely your choice. The exact line is shown in the code below; it links to the tool with rel="nofollow".
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Starting values
One item per line. Long content is carried after the # in the embed code, so it never reaches a server.
Leave blank to use the widget's defaults. Visitors can still change every value.

Live preview

Exactly what your visitors will see

Embed code

<iframe src="https://a2z.tools/embed/w/newsletter-cta-box" title="Newsletter CTA Box by A2Z Tools" width="100%" height="490" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.

Works with

How it works

You write the headline, up to six benefit lines, a send-day line such as Every Tuesday morning and a privacy sentence; the box lays them out with check marks and a calendar line, and shows the host of your sign-up page under the button so readers know where they will land. A known host is named - substack.com as Substack, list-manage.com as Mailchimp, kit.com as Kit, buttondown.com as Buttondown. The subscriber count is either a whole number, grouped for the locale (12400 reads 12,400), or short text such as 12k+, always followed by a footnote that the figure comes from you. Email pre-fill is off by default. Turned on, and only with the name of your form's email parameter, a box appears; a valid address is URL-encoded into your link - jo+[email protected] becomes jo%2Bnews%40acme.example - and a malformed one is left out. The box states that the address will appear in your page's address bar, logs and the visitor's history.

Method

  • Subscribe link = your https sign-up page, unchanged when pre-fill is off
  • Pre-fill on: link + ?<email parameter>=<address> via URLSearchParams (application/x-www-form-urlencoded: @ -> %40, + -> %2B), only for an address matching [email protected]
  • Subscriber count: integer -> locale grouping (Intl.NumberFormat); anything else shown as typed, max 24 characters

Worked examples

Default sample

Inputs: No settings

Result: Subscribe free -> https://fieldnotes.example/subscribe; 12,400 gardeners already read it*

Pre-fill is off, so the link carries nothing but your page address.

Mailchimp pre-fill

Inputs: url=https://acme.us1.list-manage.com/subscribe?u=1&id=2; prefill=1; emailParam=EMAIL; visitor types [email protected]

Result: https://acme.us1.list-manage.com/subscribe?u=1&id=2&EMAIL=jo%40acme.example

Existing parameters are kept and @ is encoded as %40.

Malformed address

Inputs: prefill on; visitor types [email protected]&admin=1

Result: Link unchanged (no EMAIL parameter)

Only a well-formed address is ever added.

Limitations

  • The box cannot tell whether someone subscribed; count sign-ups in your email provider.
  • Pre-fill depends on your provider reading an address from the URL, and puts that address in the link when used.
  • The subscriber figure is static text from the embed code.

Where publishers use it

  • End of every blog post on a WordPress or Ghost site, pointing to a Substack publication
  • A shop's footer inviting customers to a Mailchimp list of new arrivals
  • A podcast website promoting the weekly show-notes email hosted on Buttondown
  • A conference or meetup page gathering interest for next year's announcement list
  • A creator's link-in-bio or about page offering a Kit (ConvertKit) landing page

Questions

Why does the button open another page instead of taking the email here?

Because A2Z collects no personal data. Your email provider already runs a hosted sign-up page that handles consent, double opt-in and unsubscribe records properly; the box sends readers there. The frame's security policy forbids form posts entirely, so an address typed in the box can only ever travel inside your own link after a click.

Where do I find my sign-up page address?

Substack: your publication address with /subscribe, for example https://yourname.substack.com/subscribe. Mailchimp: Audience > Signup forms > Form builder gives a hosted form URL on list-manage.com or eepurl.com. Buttondown: https://buttondown.com/yourname. Kit: the URL of a landing page you publish. Any other https page works the same way.

Should I turn on email pre-fill?

Only if your sign-up page reads an address from its URL and you accept the trade-off. The visitor still confirms on your page, but the address becomes part of a link, so it can sit in your web-server logs, analytics referrers and the visitor's browser history. Test the parameter name first by adding [email protected] to your page by hand, and check the exact field name in your provider's help pages.

What should the privacy line say?

Something you actually do: how often you send, that every email has an unsubscribe link, and that you do not sell the list. In the UK, PECR needs specific consent for marketing email to individuals; the US CAN-SPAM Act needs a working opt-out honoured within 10 business days and your postal address in each message. Your provider's form usually covers the consent wording.

Is the subscriber count checked?

No. It is a figure you enter, shown with an asterisk and the line Subscriber figure reported by the publisher. Leave it blank if your list is small or you prefer not to show it. Keep it honest; an inflated count is a misleading claim under consumer-protection law in most countries.

Which layout should I use?

Card stacks everything in one tinted panel and suits sidebars and the end of articles. Banner is a slimmer band whose benefit lines sit in two columns when the frame is at least 520 px wide, with the button sized to its label - good between sections of a long page.

Sources

  1. Electronic mail marketing (Guide to PECR) - Information Commissioner's Office . Specific consent for marketing email to individuals, the soft opt-in for existing customers, and an opt-out in every message. Checked 2026-10-01.
  2. CAN-SPAM Act: A Compliance Guide for Business - US Federal Trade Commission . Postal address in each message, a clear opt-out, and opt-outs honoured within 10 business days. Checked 2026-10-01.

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools Newsletter CTA Box
https://a2z.tools/embed/newsletter-cta-box

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