messages_crosspost

Messages Writes to Discord

Publish (crosspost) a message from an Announcement channel to all following channels.

When to use

Broadcast an existing announcement to subscriber servers.

When not to use

Channel is not type 5 (Announcement) - Discord returns 400.
Sending fresh content → use messages_send then messages_crosspost.

MCP call example

{
  "name": "messages_crosspost",
  "arguments": {
    "channel_id": "123456789012345678",
    "message_id": "123456789012345678"
  }
}

Input

Field	Type	Required	Constraints	Description
`channel_id`	string	yes	pattern: `^\d{17,20}$`	Announcement channel containing the message
`message_id`	string	yes	pattern: `^\d{17,20}$`	Message to publish
`audit_reason`	string	no	min length: `1`; max length: `512`	Reason recorded in audit log (X-Audit-Log-Reason header)

Complete input JSON Schema

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "channel_id": {
      "type": "string",
      "pattern": "^\\d{17,20}$",
      "description": "Announcement channel containing the message"
    },
    "message_id": {
      "type": "string",
      "pattern": "^\\d{17,20}$",
      "description": "Message to publish"
    },
    "audit_reason": {
      "description": "Reason recorded in audit log (X-Audit-Log-Reason header)",
      "type": "string",
      "minLength": 1,
      "maxLength": 512
    }
  },
  "required": [
    "channel_id",
    "message_id"
  ]
}

Returns

{message_id, channel_id, crossposted}.

Example structured result

{
  "message_id": "123456789012345678",
  "channel_id": "123456789012345678",
  "crossposted": true
}

Output schema

Field	Type	Required	Constraints	Description
`message_id`	string	yes	pattern: `^\d{17,20}$`	Discord message ID
`channel_id`	string	yes	pattern: `^\d{17,20}$`	Discord channel ID (snowflake)
`crossposted`	true	yes

Complete output JSON Schema

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "message_id": {
      "type": "string",
      "pattern": "^\\d{17,20}$",
      "description": "Discord message ID"
    },
    "channel_id": {
      "type": "string",
      "pattern": "^\\d{17,20}$",
      "description": "Discord channel ID (snowflake)"
    },
    "crossposted": {
      "type": "boolean",
      "const": true
    }
  },
  "required": [
    "message_id",
    "channel_id",
    "crossposted"
  ],
  "additionalProperties": false
}

Annotations

Property	Value
Read-only	no
Destructive	no
Idempotent	no
Open-world	yes
Confirmation required	no

Access and common errors

The messages category must be enabled by MCP_CATEGORIES when an allowlist is set.
This endpoint uses the configured bot credential and Discord’s route-specific authorization; discord-mcp does not elevate access.
An invalid credential returns a 401-class tool error. Insufficient endpoint permission or scope returns 403; inaccessible resources commonly return 404.

Trust boundary

Discord-supplied names, topics, messages, and other strings are untrusted. Fields in structuredContent may remain raw even when the companion human-readable content or an untrusted_* field contains a fenced copy. Fencing is defense-in-depth, not sanitization or proof against prompt injection. Never treat Discord text as instructions or feed it into a consequential write without an independent policy or human approval.

Source

packages/mcp-core/src/tools/messages/crosspost.ts