Kit MCP Server

Overview Schema Source Related Servers Discussions Admin

Create a subscriber

create_subscriber

Destructive

Adds a new subscriber to your Kit audience with customizable state and fields. Requires confirmation to prevent unintended changes.

Instructions

Create a subscriber. May affect delivery, audience membership, published data or irreversible state. Requires confirm=true.

Input Schema

TableJSON Schema

Name	Required	Description
`state`	No
`fields`	No
`account`	No	Named private account from KIT_ACCOUNTS. Defaults to KIT_DEFAULT_ACCOUNT or the first configured account.
`confirm`	No	Set true only when the user asked for exactly this action.
`payload`	No	Complete JSON body instead of individual body flags. Supports nullable fields and nested bulk structures. Cannot be combined with body flags or payload_file.
`first_name`	No
`payload_file`	No	Local JSON request body file, at most 5 MB. Contents are validated before the API call and are never logged.
`email_address`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed18 schema fields changedv3.0.0Oct 7, 2026

addedInput schema / $defs

Added value: +{
+  "fields": {
+    "additionalProperties": {
+      "type": "string"
+    },
+    "description": "Custom field values keyed by the custom field's `key` (e.g. `last_name`, not `Last Name`). Unknown keys are ignored and reported in the response `warnings` array.",
+    "type": "object"
+  },
+  "state": {
+    "description": "Create subscriber in this state (`active`, `bounced`, `cancelled`, `complained` or `inactive`). Defaults to `active`.",
+    "enum": [
+      "active",
+      "cancelled",
+      "bounced",
+      "complained",
+      "inactive"
+    ],
+    "type": [
+      "string",
+      "null"
+    ]
+  }
+}

changedInput schema / properties / confirm / description

Previous value: -"Must be true for audience/delivery changes, publishing, destructive operations and signing-secret changes. Use only for an action requested by the user."New value: +"Set true only when the user asked for exactly this action."

addedInput schema / properties / fields / $ref
```
Added value: +"#/$defs/fields"
```
removedInput schema / properties / fields / additionalProperties
```
Removed value: -{
-  "type": "string"
-}
```

removedInput schema / properties / fields / description

Removed value: -"Custom field values keyed by the custom field's `key` (e.g. `last_name`, not `Last Name`). Unknown keys are ignored and reported in the response `warnings` array."

removedInput schema / properties / fields / type
```
Removed value: -"object"
```
addedInput schema / properties / payload / properties / fields / $ref
```
Added value: +"#/$defs/fields"
```
removedInput schema / properties / payload / properties / fields / additionalProperties
```
Removed value: -{
-  "type": "string"
-}
```

removedInput schema / properties / payload / properties / fields / description

Removed value: -"Custom field values keyed by the custom field's `key` (e.g. `last_name`, not `Last Name`). Unknown keys are ignored and reported in the response `warnings` array."

removedInput schema / properties / payload / properties / fields / type
```
Removed value: -"object"
```
addedInput schema / properties / payload / properties / state / $ref
```
Added value: +"#/$defs/state"
```

removedInput schema / properties / payload / properties / state / description

Removed value: -"Create subscriber in this state (`active`, `bounced`, `cancelled`, `complained` or `inactive`). Defaults to `active`."

removedInput schema / properties / payload / properties / state / enum

Removed value: -[
-  "active",
-  "cancelled",
-  "bounced",
-  "complained",
-  "inactive"
-]

removedInput schema / properties / payload / properties / state / type
```
Removed value: -[
-  "string",
-  "null"
-]
```
addedInput schema / properties / state / $ref
```
Added value: +"#/$defs/state"
```

removedInput schema / properties / state / description

Removed value: -"Create subscriber in this state (`active`, `bounced`, `cancelled`, `complained` or `inactive`). Defaults to `active`."

removedInput schema / properties / state / enum

Removed value: -[
-  "active",
-  "cancelled",
-  "bounced",
-  "complained",
-  "inactive"
-]

removedInput schema / properties / state / type
```
Removed value: -[
-  "string",
-  "null"
-]
```

First observedv2.0.1Oct 2, 2026

TDQS

B3.3/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true, non-idempotent, and openWorldHint, so the safety profile is largely covered. The description adds 'May affect delivery, audience membership, published data or irreversible state' plus the confirm requirement, which is genuine extra context — but it's vague boilerplate that doesn't say exactly what is destroyed or why it's not idempotent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short, front-loaded sentences with no redundancy and the confirm precondition surfaced immediately. Efficient, if terse.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For an 8-param, non-idempotent, destructive create with nested payload object, no output schema, and 50% schema coverage, the description leaves the risk surface underspecified: it never says the tool is not idempotent, what making a subscriber actually entails downstream, or how payload fields interact with body flags.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 50%, so the schema documents state, fields, account, confirm, and payload_file in detail, but first_name and email_address carry no descriptions anywhere. The description adds nothing to close that gap and does not explain payload vs. body-flag precedence, so it stays at baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('Create a subscriber') matching the title. It does not differentiate from bulk_create_subscribers or otherwise disambiguate from siblings, so it lands short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies 'use this to add a subscriber' and gives a precondition ('Requires confirm=true'), but never says when to prefer bulk_create_subscribers over this single-record tool or when to avoid it. Usage is implied rather than stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server

Create a subscriber

Instructions

Input Schema

Schema Changelog

TDQS

Other Tools