How to Integrate ConvertKit with Your Headless CMS

What is ConvertKit?

ConvertKit, now branded as Kit, is an email marketing platform for creators, newsletter teams, educators, and small businesses that sell digital products or grow audiences through email. It includes subscriber forms, landing pages, tags, segments, broadcasts, visual automations, and commerce tools. Its core job is turning audience actions, like downloading a guide or joining a course waitlist, into targeted email follow-up.

Why integrate ConvertKit with a headless CMS?

Marketing teams often create the same campaign content in two places: the website and ConvertKit. A product marketer publishes a new guide, then someone else copies the title, description, image, URL, category, and CTA into a ConvertKit form, tag, or automation. That works for 3 lead magnets. It breaks down when you have 60 resources, 12 audience segments, 4 locales, and weekly launches.

Connecting ConvertKit to a headless CMS lets your publishing workflow trigger your email workflow. When a resource goes live, a webhook can send the right fields to ConvertKit, apply a tag like "interest:paid-newsletter," subscribe a user through a form endpoint, or update metadata used by a campaign. With Sanity, content is structured in the Content Lake as typed JSON, so you can query exactly what ConvertKit needs with GROQ instead of parsing HTML from a rendered page.

The trade-off is that you need to define the rules up front. Which content types should sync? Which tags are allowed? What happens if ConvertKit rejects an email address or a form ID changes? Once those decisions are in code, the day-to-day workflow gets much cleaner: editors publish in Sanity Studio, and ConvertKit receives consistent campaign data from the same source that powers your site, app, and other channels.

Architecture overview

A common setup starts in Sanity Studio, where editors model resources, newsletters, courses, or landing pages with fields like title, slug, excerpt, audience segment, ConvertKit form ID, ConvertKit tag ID, publish status, and canonical URL. When a document is published, a Sanity webhook fires. You can route that webhook to a Sanity Function or to your own API route. The handler receives the mutation event, uses @sanity/client to fetch the full document from the Content Lake, and runs a GROQ query that selects only the fields ConvertKit needs. For example, you might join an article to its author, topic, and audience segment, then return a compact payload with title, URL, form ID, tag IDs, and email CTA copy. From there, the handler calls ConvertKit's API over HTTPS. For subscriber capture, it can POST to /v3/forms/{form_id}/subscribe with api_key, email, first_name, fields, and tags. For tagging an existing subscriber, it can POST to /v3/tags/{tag_id}/subscribe. The end user sees the result on your site as a form, content upgrade, newsletter signup, or gated resource, while ConvertKit receives clean subscriber data tied back to the content that caused the signup.

Common use cases

Step-by-step integration

1. 1

   Set up ConvertKit access

   Create or log in to your ConvertKit account, then go to Settings and copy your API key. Create the forms and tags you plan to use, and note each form ID and tag ID from the ConvertKit URLs or API responses.

2. 2

   Install the packages you need

   In your webhook or Sanity Function project, install @sanity/client. You can call ConvertKit with fetch because its v3 API is HTTPS-based and accepts JSON or form-encoded payloads.

3. 3

   Model campaign-ready content in Sanity Studio

   Add fields such as title, slug, excerpt, audienceSegment, convertKitFormId, convertKitTagIds, ctaText, and gatedAssetUrl. Keep ConvertKit IDs in dedicated fields instead of hiding them in rich text.

4. 4

   Create the sync trigger

   Configure a Sanity webhook to fire on publish events for the relevant document types, or use a Sanity Function if you want the server-side logic to run close to your content events without hosting another service.

5. 5

   Call the ConvertKit API

   Use GROQ to fetch the published document from the Content Lake, then POST to ConvertKit's form or tag endpoints. Store API keys in environment variables, not in Sanity documents or frontend code.

6. 6

   Test the full signup path

   Publish a draft resource, submit the frontend form with a test email address, confirm the subscriber appears in ConvertKit, check the expected tags, and verify the user receives the right automation sequence.

Code example

import {createClient} from '@sanity/client'

const sanity = createClient({
  projectId: process.env.SANITY_PROJECT_ID!,
  dataset: process.env.SANITY_DATASET!,
  apiVersion: '2025-01-01',
  token: process.env.SANITY_READ_TOKEN,
  useCdn: false,
})

export async function POST(req: Request) {
  const {documentId, email, firstName} = await req.json()

  const resource = await sanity.fetch(`
    *[_id == $id][0]{
      title,
      "url": "https://example.com/resources/" + slug.current,
      convertKitFormId,
      convertKitTagIds
    }
  `, {id: documentId})

  const res = await fetch(
    `https://api.convertkit.com/v3/forms/${resource.convertKitFormId}/subscribe`,
    {
      method: 'POST',
      headers: {'Content-Type': 'application/json'},
      body: JSON.stringify({
        api_key: process.env.CONVERTKIT_API_KEY,
        email,
        first_name: firstName,
        tags: resource.convertKitTagIds,
        fields: {
          source_resource: resource.title,
          source_url: resource.url
        }
      })
    }
  )

  if (!res.ok) return new Response(await res.text(), {status: res.status})
  return Response.json({ok: true})
}

How Sanity + ConvertKit works

CMS approaches to ConvertKit

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