ConvertKit

Overview

ConvertKit (rebranded Kit in 2024) is an email marketing and creator monetisation platform founded in 2013 by Nathan Barry and headquartered in Boise, Idaho. It is purpose-built for bloggers, podcasters, newsletter writers, course creators, and online educators — the "creator economy" segment. ConvertKit provides embeddable subscriber signup forms, hosted landing pages, automated email sequences, and a commerce layer for selling digital products and paid newsletters. As of 2024, ConvertKit serves over 600,000 creators and manages billions of email sends annually.

What This Script Does

The ConvertKit script loads from f.convertkit.com and renders embeddable signup forms and call-to-action widgets. Forms may appear as inline page embeds, slide-in overlays, or modal popups depending on the creator's configuration.

Cookies and identifiers set:

• ck_subscriber_id — First-party cookie set on the host domain when a visitor submits a ConvertKit form or arrives via a ConvertKit email link; links the browser session to the ConvertKit subscriber record; expiry 1 year. This is the primary identifier for automation and tagging.
• ck_session — Session cookie tracking the current visit for form display logic (e.g., suppressing repeat popups); expires at session end.
• Local storage key convertkit_form_shown — Records which form IDs have already been displayed to prevent repeat prompting within a session.

Script filenames and CDN: ck.js loaded from f.convertkit.com; form configuration fetched from api.convertkit.com/v3/forms/<form-id>/; submission POSTed to api.convertkit.com/v3/forms/<form-id>/subscribe.

Per-submission data collected:

• Email address (required field)
• Optional additional fields: first name, custom fields defined by the creator
• Source URL and referrer at time of form submission
• UTM campaign parameters for signup attribution
• Tag assignments based on the form or landing page the visitor subscribed through
• ConvertKit sequence assignment (which email automation flow is triggered)

Tracking pixels in emails: ConvertKit emails include tracking pixels (open.convertkit.com) and click-redirect links (click.convertkit.com) that report open rates and click-throughs back to the creator's analytics dashboard. These operate in the email context rather than on the host website, but link clicks return the viewer to the host site with referral attribution.

Consent & Compliance

ConvertKit scripts are classified under the marketing category. The form widgets collect personal data (email addresses) and transmit them to a third-party US-based marketing service for list management and automated email campaigns. Under GDPR Article 6(1)(a), this requires explicit prior consent — both for the cookie-based subscriber identification and for the email marketing processing itself. The form submission itself constitutes the consent moment for the email subscription, but the ck_subscriber_id cookie that links subsequent browsing to the subscriber record requires separate ePrivacy consent. ConvertKit participates in the EU-US Data Privacy Framework, enabling compliant data transfers. Under CCPA/CPRA, email collection and marketing automation constitute processing of personal information that must be disclosed with opt-out rights.

Should You Block This Without Consent?

Yes. ConvertKit scripts collect personal data for email marketing and set cookies that identify subscribers across visits. Block the ConvertKit script until marketing consent is granted. The signup form's visual presentation does not require the script; only the data capture and transmission does.