The Custom Fields API from Kit — 4 operation(s) for custom fields.
Each operation below carries the questions people ask an LLM about it and the instructions they give an agent to run it. Generated by API Evangelist overlay
Every API here is available over the APIs.io API and to AI agents over MCP.
One button, every client — Claude, Cursor, VS Code and the rest.
https://apis.io/mcp
find_apisBrowse and filter every API in the catalog.get_api_artifactsOne API's artifacts, grouped by type.get_openapiThe primary OpenAPI for this API.find_similar_apisAPIs that look like this one.apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.resolveTurn a domain, URL or GitHub org into the provider it belongs to.find_cohortsEvery scored population of providers in the catalog.curl "https://apis.io/api/v1/apis/convertkit:convertkit-custom-fields-api"curl "https://apis.io/api/v1/apis?limit=25"Discovery needs no key. Ratings and market analysis are Pro.
Free tier, no form to fill in. Signing in shares your email address with us — we store it to create your key and to recognise you if you sign in with another provider. See our Privacy Policy and Terms.
A second provider on the same verified email joins the account you already have.
openapi: 3.2.0
info:
title: Kit Custom Fields API
version: '4.0'
servers:
- url: https://api.kit.com
tags:
- name: Custom Fields
paths:
/v4/bulk/custom_fields:
post:
summary: Bulk create custom fields
description: See "Bulk & async processing" for more information.
tags:
- Custom Fields
security:
- OAuth2: []
parameters: []
responses:
'200':
description: Creates the custom_fields synchronously when 100 or less custom fields are requested
content:
application/json:
schema:
type: object
properties:
custom_fields:
type: array
items:
type: object
properties:
id:
type: integer
label:
type: string
key:
type: string
name:
type: string
created_at:
type: string
required:
- id
- key
- label
- name
- created_at
failures:
type: array
items: {}
required:
- custom_fields
- failures
example:
custom_fields:
- id: 143
key: existing_custom_field
label: Existing Custom Field
name: ck_field_143_existing_custom_field
created_at: '2023-02-17T11:43:55Z'
- id: 145
key: interests
label: Interests
name: ck_field_145_interests
created_at: '2023-02-17T11:43:55Z'
- id: 144
key: last_name
label: Last name
name: ck_field_144_last_name
created_at: '2023-02-17T11:43:55Z'
failures: []
'202':
description: Creates or updates custom_fields asynchronously when more than 100 custom fields are requested
content:
application/json:
schema:
type: object
properties: {}
example: {}
'401':
description: Returns a 401 if the token and/or account cannot be authenticated
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- The access token is invalid
'413':
description: Returns a 413 when the size of the request would exceed the account's data limit for enqueued bulk requests
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- This request exceeds your queued bulk requests limit. Please wait while we process your existing requests and try again later.
'422':
description: Returns a 422 when `custom_fields` is empty or not an array
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- No custom fields included for processing
requestBody:
content:
application/json:
schema:
type: object
properties:
custom_fields:
type: array
items:
type: object
properties:
label:
type: string
required:
- label
callback_url:
type:
- string
- 'null'
required:
- custom_fields
example:
custom_fields:
- label: Test Custom Field 0
- label: Test Custom Field 1
- label: Test Custom Field 2
- label: Test Custom Field 3
callback_url: null
operationId: postV4BulkCustomFields
x-operation-id-source: derived
/v4/bulk/custom_fields/subscribers:
post:
summary: Bulk update subscriber custom field values
tags:
- Custom Fields
security:
- OAuth2: []
parameters: []
responses:
'200':
description: Creates or updates custom field values synchronously when 100 or less values are requested
content:
application/json:
schema:
type: object
properties:
custom_field_values:
type: array
items:
type: object
properties:
subscriber_id:
type: integer
subscriber_custom_field_id:
type: integer
value:
type: string
required:
- subscriber_id
- subscriber_custom_field_id
- value
failures:
type: array
items:
type: object
properties:
errors:
type: array
items:
type: string
custom_field_value:
type: object
properties:
subscriber_id:
type:
- integer
- 'null'
subscriber_custom_field_id:
type: integer
value:
type: string
required:
- subscriber_id
- subscriber_custom_field_id
- value
required:
- errors
- custom_field_value
required:
- custom_field_values
- failures
example:
custom_field_values:
- subscriber_id: 615
subscriber_custom_field_id: 156
value: Smith
- subscriber_id: 615
subscriber_custom_field_id: 157
value: Acme Inc
failures:
- errors:
- Subscriber does not exist
custom_field_value:
subscriber_id: null
subscriber_custom_field_id: 156
value: Jones
- errors:
- Custom field does not exist
custom_field_value:
subscriber_id: 615
subscriber_custom_field_id: 999999
value: Test
'202':
description: Creates or updates custom field values asynchronously when more than 100 values are requested
content:
application/json:
schema:
type: object
properties: {}
example: {}
'401':
description: Returns a 401 if the token and/or account cannot be authenticated
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- The access token is invalid
'413':
description: Returns a 413 when the size of the request would exceed the account's data limit for enqueued bulk requests
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- This request exceeds your queued bulk requests limit. Please wait while we process your existing requests and try again later.
'422':
description: Returns a 422 when `custom_field_values` is empty or not an array
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- No custom field values included for processing
requestBody:
content:
application/json:
schema:
type: object
properties:
custom_field_values:
type: array
items:
type: object
properties:
subscriber_id:
type:
- integer
- 'null'
subscriber_custom_field_id:
type: integer
value:
type: string
required:
- subscriber_id
- subscriber_custom_field_id
- value
callback_url: {}
required:
- custom_field_values
- callback_url
example:
custom_field_values:
- subscriber_id: 0
subscriber_custom_field_id: 0
value: value_0
- subscriber_id: 1
subscriber_custom_field_id: 1
value: value_1
- subscriber_id: 2
subscriber_custom_field_id: 2
value: value_2
- subscriber_id: 3
subscriber_custom_field_id: 3
value: value_3
callback_url: null
operationId: postV4BulkCustomFieldsSubscribers
x-operation-id-source: derived
/v4/custom_fields:
get:
summary: List custom fields
description: 'A custom field allows you to collect subscriber information beyond the standard fields of first name and email address. An example would be a custom field called last name so you can get the full names of your subscribers.
You create a custom field, and then you''re able to use that in your forms or emails.'
tags:
- Custom Fields
security:
- API Key: []
- OAuth2: []
parameters:
- name: after
description: To fetch next page of results, use `?after=<end_cursor>`
in: query
required: false
schema: {}
- name: before
description: To fetch previous page of results, use `?before=<start_cursor>`
in: query
required: false
schema: {}
- name: include_total_count
description: Set to `true` to include the `total_count` in the response. This option can cause slow responses; if paging through results, request it only on the first page and reuse the value for subsequent pages.
in: query
required: false
schema:
type: boolean
example: false
- name: per_page
description: Number of results per page. Default 500, maximum 1000.
in: query
required: false
schema: {}
responses:
'200':
description: Returns a paginated list of all custom fields for your account
content:
application/json:
schema:
type: object
properties:
custom_fields:
type: array
items:
type: object
properties:
id:
type: integer
name:
type: string
key:
type: string
label:
type: string
required:
- id
- name
- key
- label
pagination:
type: object
properties:
has_previous_page:
type: boolean
has_next_page:
type: boolean
start_cursor:
type: string
end_cursor:
type: string
per_page:
type: integer
required:
- has_previous_page
- has_next_page
- start_cursor
- end_cursor
- per_page
required:
- custom_fields
- pagination
example:
custom_fields:
- id: 1
name: ck_field_1_last_name
key: last_name
label: Last name
pagination:
has_previous_page: false
has_next_page: false
start_cursor: WzFd
end_cursor: WzFd
per_page: 500
'401':
description: Returns a 401 if the token and/or account cannot be authenticated
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- The access token is invalid
x-mcp:
enabled: true
operationId: getV4CustomFields
x-operation-id-source: derived
post:
summary: Create a custom field
description: 'Create a custom field for your account. The label field must be unique to your account. Whitespace will be removed from the beginning and the end of your label.
Additionally, a key field and a name field will be generated for you. The key is an ASCII-only, lowercased, underscored representation of your label. This key must be unique to your account. Keys are used in personalization tags in sequences and broadcasts. Names are unique identifiers for use in the HTML of custom forms. They are made up of a combination of ID and the key of the custom field prefixed with "ck_field".'
tags:
- Custom Fields
security:
- API Key: []
- OAuth2: []
parameters: []
responses:
'200':
description: Returns a 200 and the custom field if it already exists
content:
application/json:
schema:
type: object
properties:
custom_field:
type: object
properties:
id:
type: integer
name:
type: string
key:
type: string
label:
type: string
required:
- id
- name
- key
- label
required:
- custom_field
example:
custom_field:
id: 8
name: ck_field_8_interests
key: interests
label: Interests
'201':
description: Creates a new custom field and returns its details
content:
application/json:
schema:
type: object
properties:
custom_field:
type: object
properties:
id:
type: integer
name:
type: string
key:
type: string
label:
type: string
required:
- id
- name
- key
- label
required:
- custom_field
example:
custom_field:
id: 6
name: ck_field_6_interests
key: interests
label: Interests
'401':
description: Returns a 401 if the token and/or account cannot be authenticated
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- The access token is invalid
'422':
description: Returns a 422 with an error message when the label is missing
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- Label can't be blank
requestBody:
content:
application/json:
schema:
type: object
properties:
label:
type: string
required:
- label
example:
label: Interests
x-mcp:
enabled: true
operationId: postV4CustomFields
x-operation-id-source: derived
/v4/custom_fields/{id}:
delete:
summary: Delete custom field
description: This will remove all data in this field from your subscribers.
tags:
- Custom Fields
security:
- API Key: []
- OAuth2: []
parameters:
- name: id
in: path
required: true
schema:
type: integer
example: 50
responses:
'204':
description: Deletes the custom field
'401':
description: Returns a 401 if the token and/or account cannot be authenticated
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- The access token is invalid
'404':
description: Returns a 404 when the provided id does not exist
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- Not Found
'422':
description: Returns a 422 when the custom field cannot be deleted
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- Unable to destroy the custom field.
x-mcp:
enabled: true
operationId: deleteV4CustomFieldsById
x-operation-id-source: derived
put:
summary: Update a custom field
description: 'Updates a custom field label (see Create a custom field for more information on labels). Note that the key will change but the name remains the same when the label is updated.
Warning: An update to a custom field will break all of the liquid personalization tags in emails that reference it - e.g. if you update a `Zip_Code` custom field to `Post_Code`, all liquid tags referencing `{{ subscriber.Zip_Code }}` would no longer work and need to be replaced with `{{ subscriber.Post_Code }}`.'
tags:
- Custom Fields
security:
- API Key: []
- OAuth2: []
parameters:
- name: id
in: path
required: true
schema:
type: integer
example: 29
responses:
'200':
description: Updates the custom field and returns its details
content:
application/json:
schema:
type: object
properties:
custom_field:
type: object
properties:
id:
type: integer
name:
type: string
key:
type: string
label:
type: string
required:
- id
- name
- key
- label
required:
- custom_field
example:
custom_field:
id: 27
name: ck_field_27_last_name
key: lastname
label: Last name
'401':
description: Returns a 401 if the token and/or account cannot be authenticated
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- The access token is invalid
'404':
description: Returns a 404 when the provided id does not exist
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- Not Found
'422':
description: Returns a 422 with an error mesage when one or more of the parameters are invalid
content:
application/json:
schema:
type: object
properties:
errors:
type: array
items:
type: string
required:
- errors
example:
errors:
- Label can't be blank
requestBody:
content:
application/json:
schema:
type: object
properties:
label:
type: string
required:
- label
example:
label: Last name
x-mcp:
enabled: true
operationId: putV4CustomFieldsById
x-operation-id-source: derived
components:
securitySchemes:
API_Key:
description: Authenticate API requests via an API Key
type: apiKey
in: header
name: X-Kit-Api-Key
OAuth2:
description: Authenticate API requests via an OAuth token
type: oauth2
flows:
authorizationCode:
authorizationUrl: https://api.kit.com/v4/oauth/authorize
tokenUrl: https://api.kit.com/v4/oauth/token
refreshUrl: https://api.kit.com/v4/oauth/token
scopes:
read: Read access to Kit API v4
write: Write access to Kit API v4
x-mint:
mcp:
enabled: true