Mailercloud

update_campaign

DestructiveIdempotent

Update a draft campaign. Only the fields you pass are changed. list_ids REPLACES the full current list set (and replaces a segment target): to add or remove a list, prefer add_lists_to_campaign / remove_lists_from_campaign. segment_id sends to one segment instead of lists. Exclusions (excluded lists, segments, tags) and frequency cap cannot be changed here: they can only be set at creation (create_campaign) or in the panel. Setting scheduled_at publishes the campaign for sending, so it takes two steps: call first without confirm to get a preview (nothing is changed), get an explicit yes from the user, then call again with confirm: true. Set dry_run: true to see the exact fields that would be sent without changing anything.

Input Schema

Name	Required	Description
`html`	No	HTML email content
`name`	No	Campaign name
`rules`	No	Send rules object: limit (number of contacts), contacts_order (first or last)
`tag_id`	No	Campaign tag ID
`confirm`	No	Must be true when scheduled_at is set, because that schedules the campaign to send. Leave false first to get a preview; nothing is changed
`dry_run`	No	Validate inputs and show what would be sent without changing anything, even when confirm is true
`subject`	No	Email subject line
`list_ids`	No	List IDs to send to (max 150). REPLACES the campaign's full recipient list set, and replaces a segment if the campaign sends to one: to add a list, include the current lists as well (or use add_lists_to_campaign)
`reply_id`	No	Pre-configured reply email ID
`plain_text`	No	Plain text content
`segment_id`	No	One segment ID to send to. Replaces the campaign's lists. Give list_ids or segment_id, not both
`campaign_id`	Yes	Campaign ID
`pause_rules`	No	pause rules object as in the panel: pause_target, pause_limit, pause_criteria, pause_condition
`reply_email`	No	Reply-to email address
`report_spam`	No	Add a report-abuse link
`sender_name`	No	Sender display name (give together with sender_email)
`scheduled_at`	No	Schedule datetime (YYYY-MM-DD HH:MM:SS, account timezone). Setting it PUBLISHES the campaign for sending at that time, so it requires confirm: true
`sender_email`	No	Sender email address (give together with sender_name)
`viewin_browser`	No	Add a view-in-browser link
`email_preheader`	No	Email preheader text (max 150 chars)
`mailing_preference`	No	Add a mailing-preference link
`permission_reminder`	No	Permission reminder text (3-150 chars)

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 23, 2026
- changedInput schema / properties / campaign_id / description
```
Previous value: -"Campaign ID,required"New value: +"Campaign ID"
```

Changed16 schema fields changedOct 23, 2026

addedInput schema / properties / confirm

Added value: +{
+  "description": "Must be true when scheduled_at is set, because that schedules the campaign to send. Leave false first to get a preview; nothing is changed",
+  "type": "boolean"
+}

changedInput schema / properties / dry_run / description

Previous value: -"Validate inputs and show what would be sent without changing anything"New value: +"Validate inputs and show what would be sent without changing anything, even when confirm is true"

removedInput schema / properties / exclude_list_ids

Removed value: -{
-  "description": "List IDs to exclude from send (replaces the current set)",
-  "items": {
-    "type": "string"
-  },
-  "type": [
-    "null",
-    "array"
-  ]
-}

removedInput schema / properties / exclude_segments

Removed value: -{
-  "description": "Segment IDs to exclude from send (replaces the current set)",
-  "items": {
-    "type": "string"
-  },
-  "type": [
-    "null",
-    "array"
-  ]
-}

removedInput schema / properties / exclude_tag_ids

Removed value: -{
-  "description": "Tag IDs to exclude from send (replaces the current set)",
-  "items": {
-    "type": "string"
-  },
-  "type": [
-    "null",
-    "array"
-  ]
-}

removedInput schema / properties / frequency_cap

Removed value: -{
-  "description": "Frequency cap (daily, weekly, etc)",
-  "type": "string"
-}

changedInput schema / properties / list_ids / description

Previous value: -"List IDs to send to. REPLACES the campaign's full recipient list set: to add a list, include the current lists as well"New value: +"List IDs to send to (max 150). REPLACES the campaign's full recipient list set, and replaces a segment if the campaign sends to one: to add a list, include the current lists as well (or use add_lists_to_campaign)"

addedInput schema / properties / mailing_preference

Added value: +{
+  "description": "Add a mailing-preference link",
+  "type": [
+    "null",
+    "boolean"
+  ]
+}

addedInput schema / properties / permission_reminder

Added value: +{
+  "description": "Permission reminder text (3-150 chars)",
+  "type": "string"
+}

addedInput schema / properties / report_spam

Added value: +{
+  "description": "Add a report-abuse link",
+  "type": [
+    "null",
+    "boolean"
+  ]
+}

changedInput schema / properties / scheduled_at / description

Previous value: -"Schedule datetime (YYYY-MM-DD HH:MM:SS, account timezone)"New value: +"Schedule datetime (YYYY-MM-DD HH:MM:SS, account timezone). Setting it PUBLISHES the campaign for sending at that time, so it requires confirm: true"

addedInput schema / properties / segment_id

Added value: +{
+  "description": "One segment ID to send to. Replaces the campaign's lists. Give list_ids or segment_id, not both",
+  "type": "string"
+}

removedInput schema / properties / segments

Removed value: -{
-  "description": "Segment IDs to send to (replaces the current set)",
-  "items": {
-    "type": "string"
-  },
-  "type": [
-    "null",
-    "array"
-  ]
-}

removedInput schema / properties / sender_id

Removed value: -{
-  "description": "Pre-configured sender ID(s) (alternative to sender_name/sender_email)",
-  "items": {
-    "type": "string"
-  },
-  "type": [
-    "null",
-    "array"
-  ]
-}

addedInput schema / properties / tag_id

Added value: +{
+  "description": "Campaign tag ID",
+  "type": "string"
+}

removedInput schema / properties / tag_ids

Removed value: -{
-  "description": "Campaign tag IDs (replaces the current set)",
-  "items": {
-    "type": "string"
-  },
-  "type": [
-    "null",
-    "array"
-  ]
-}

Changed25 schema fields changedOct 19, 2026

removedInput schema / properties / api_key

Removed value: -{
-  "description": "MailerCloud API key",
-  "type": "string"
-}

addedInput schema / properties / dry_run

Added value: +{
+  "description": "Validate inputs and show what would be sent without changing anything",
+  "type": "boolean"
+}

addedInput schema / properties / email_preheader

Added value: +{
+  "description": "Email preheader text (max 150 chars)",
+  "type": "string"
+}

addedInput schema / properties / exclude_list_ids

Added value: +{
+  "description": "List IDs to exclude from send (replaces the current set)",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

addedInput schema / properties / exclude_segments

Added value: +{
+  "description": "Segment IDs to exclude from send (replaces the current set)",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

addedInput schema / properties / exclude_tag_ids

Added value: +{
+  "description": "Tag IDs to exclude from send (replaces the current set)",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

removedInput schema / properties / fields

Removed value: -{
-  "additionalProperties": true,
-  "description": "Fields to update,required",
-  "type": "object"
-}

addedInput schema / properties / frequency_cap

Added value: +{
+  "description": "Frequency cap (daily, weekly, etc)",
+  "type": "string"
+}

addedInput schema / properties / html

Added value: +{
+  "description": "HTML email content",
+  "type": "string"
+}

addedInput schema / properties / list_ids

Added value: +{
+  "description": "List IDs to send to. REPLACES the campaign's full recipient list set: to add a list, include the current lists as well",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

addedInput schema / properties / name

Added value: +{
+  "description": "Campaign name",
+  "type": "string"
+}

addedInput schema / properties / pause_rules

Added value: +{
+  "additionalProperties": true,
+  "description": "pause rules object as in the panel: pause_target, pause_limit, pause_criteria, pause_condition",
+  "type": "object"
+}

addedInput schema / properties / plain_text

Added value: +{
+  "description": "Plain text content",
+  "type": "string"
+}

addedInput schema / properties / reply_email

Added value: +{
+  "description": "Reply-to email address",
+  "type": "string"
+}

addedInput schema / properties / reply_id

Added value: +{
+  "description": "Pre-configured reply email ID",
+  "type": "string"
+}

addedInput schema / properties / rules

Added value: +{
+  "additionalProperties": true,
+  "description": "Send rules object: limit (number of contacts), contacts_order (first or last)",
+  "type": "object"
+}

addedInput schema / properties / scheduled_at

Added value: +{
+  "description": "Schedule datetime (YYYY-MM-DD HH:MM:SS, account timezone)",
+  "type": "string"
+}

addedInput schema / properties / segments

Added value: +{
+  "description": "Segment IDs to send to (replaces the current set)",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

addedInput schema / properties / sender_email

Added value: +{
+  "description": "Sender email address (give together with sender_name)",
+  "type": "string"
+}

addedInput schema / properties / sender_id

Added value: +{
+  "description": "Pre-configured sender ID(s) (alternative to sender_name/sender_email)",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

addedInput schema / properties / sender_name

Added value: +{
+  "description": "Sender display name (give together with sender_email)",
+  "type": "string"
+}

addedInput schema / properties / subject

Added value: +{
+  "description": "Email subject line",
+  "type": "string"
+}

addedInput schema / properties / tag_ids

Added value: +{
+  "description": "Campaign tag IDs (replaces the current set)",
+  "items": {
+    "type": "string"
+  },
+  "type": [
+    "null",
+    "array"
+  ]
+}

addedInput schema / properties / viewin_browser

Added value: +{
+  "description": "Add a view-in-browser link",
+  "type": [
+    "null",
+    "boolean"
+  ]
+}

changedInput schema / required

Previous value: -[
-  "campaign_id",
-  "fields"
-]New value: +[
+  "campaign_id"
+]

First observedSep 2, 2026

TDQS

A4.1/5.0

Behavior3/5

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

Annotations already declare destructiveHint=true, idempotentHint=true, readOnlyHint=false and openWorldHint=true, so the bar is lower. The description does add real value beyond that: partial-update semantics, the publishing side effect of scheduled_at, the confirm gate, and the fact that a preview changes nothing. It still omits auth/permission expectations and rollback behavior for a destructive 22-parameter write.

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?

Front-loaded with the purpose and the partial-update rule, then the highest-risk behavior (list_ids replacement, scheduled_at publishing, confirm, dry_run). It is a single dense paragraph that largely restates schema descriptions for list_ids, segment_id, scheduled_at, confirm and dry_run, so a small amount of redundancy remains.

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

Completeness4/5

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

For a 22-parameter, nested-object, destructive mutation with no output schema, the description covers the dangerous and ambiguous parts thoroughly. The remaining gap is what the tool returns on success versus the preview, and any permission preconditions, neither of which is stated.

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 100%, so the baseline is 3 and each parameter is already documented. The description goes beyond the schema on the cross-field interactions: list_ids replaces the whole recipient set and supersedes segment_id, and confirm is only mandatory when scheduled_at is set. That is genuine added meaning, but most other parameters get no description-level semantics.

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

Purpose5/5

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

States the specific verb and resource (update a draft campaign) plus the key scoping rule that only passed fields change. It further differentiates from siblings by naming add_lists_to_campaign / remove_lists_from_campaign and create_campaign in the contexts where they are the right alternative.

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

Usage Guidelines5/5

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

Explicitly routes the agent: use add_lists_to_campaign/remove_lists_from_campaign for incremental list edits, exclusion and frequency-cap fields must go to create_campaign or the panel, and scheduled_at requires a two-step preview-then-confirm flow with an explicit user yes. It also states dry_run as the safe inspection path.

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

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