MCP Tools Reference: pubsub.googleapis.com

Tool: publish

Publish a series of one or more messages to an existing topic.

Parameters

  • topic: The name of the topic to publish to in the format projects/{project_id}/topics/{topic_name}.

  • messages: A list of one or more messages to publish. Each message must be of type bytes. If you are given a string, you must first convert it to bytes.

Returns

  • A PublishResponse object containing the message IDs of the published messages, if successful.

  • A NOT_FOUND error if the topic does not exist.

Usage

  1. Ensure that the topic exists by calling get_topic.

  2. If the topic does not exist, return an error.

  3. Create a new byte array to hold the message data.

  4. Populate the byte array with the message data.

  5. Call publish passing the topic name and the byte array.

Important Notes

  • A project ID, topic name, and message data must be provided.

The following sample demonstrate how to use curl to invoke the publish MCP tool.

Curl Request 
                  
curl --location 'https://pubsub.googleapis.com/mcp' \
--header 'content-type: application/json' \
--header 'accept: application/json, text/event-stream' \
--data '{
  "method": "tools/call",
  "params": {
    "name": "publish",
    "arguments": {
      // provide these details according to the tool's MCP specification
    }
  },
  "jsonrpc": "2.0",
  "id": 1
}'

Input Schema

Request for the Publish method.

PublishRequest

JSON representation 
{
  "topic": string,
  "messages": [
    {
      object (PubsubMessage)
    }
  ]
}
Fields
topic

string

Required. The messages in the request will be published on this topic. Format is projects/{project}/topics/{topic}.
messages[]

object (PubsubMessage)

Required. The messages to publish.

PubsubMessage

JSON representation 
{
  "data": string,
  "attributes": {
    string: string,
    ...
  },
  "messageId": string,
  "publishTime": string,
  "orderingKey": string
}
Fields
data

string (bytes format)

Optional. The message data field. If this field is empty, the message must contain at least one attribute.

A base64-encoded string.
attributes

map (key: string, value: string)

Optional. Attributes for this message. If this field is empty, the message must contain non-empty data. This can be used to filter messages on the subscription.

An object containing a list of "key": value pairs. Example: { "name": "wrench", "mass": "1.3kg", "count": "3" }.
messageId

string

ID of this message, assigned by the server when the message is published. Guaranteed to be unique within the topic. This value may be read by a subscriber that receives a PubsubMessage via a Pull call or a push delivery. It must not be populated by the publisher in a Publish call.
publishTime

string (Timestamp format)

The time at which the message was published, populated by the server when it receives the Publish call. It must not be populated by the publisher in a Publish call.

Uses RFC 3339, where generated output will always be Z-normalized and use 0, 3, 6 or 9 fractional digits. Offsets other than "Z" are also accepted. Examples: "2014-10-02T15:01:23Z", "2014-10-02T15:01:23.045123456Z" or "2014-10-02T15:01:23+05:30".
orderingKey

string

Optional. If non-empty, identifies related messages for which publish order should be respected. If a Subscription has enable_message_ordering set to true, messages published with the same non-empty ordering_key value will be delivered to subscribers in the order in which they are received by the Pub/Sub system. All PubsubMessages published in a given PublishRequest must specify the same ordering_key value. For more information, see ordering messages.

AttributesEntry

JSON representation 
{
  "key": string,
  "value": string
}
Fields
key

string
value

string

Timestamp

JSON representation 
{
  "seconds": string,
  "nanos": integer
}
Fields
seconds

string (int64 format)

Represents seconds of UTC time since Unix epoch 1970-01-01T00:00:00Z. Must be between -62135596800 and 253402300799 inclusive (which corresponds to 0001-01-01T00:00:00Z to 9999-12-31T23:59:59Z).
nanos

integer

Non-negative fractions of a second at nanosecond resolution. This field is the nanosecond portion of the duration, not an alternative to seconds. Negative second values with fractions must still have non-negative nanos values that count forward in time. Must be between 0 and 999,999,999 inclusive.

Output Schema

Response for the Publish method.

PublishResponse

JSON representation 
{
  "messageIds": [
    string
  ]
}
Fields
messageIds[]

string

Optional. The server-assigned ID of each published message, in the same order as the messages in the request. IDs are guaranteed to be unique within the topic.

Tool Annotations

Destructive Hint: ❌ | Idempotent Hint: ❌ | Read Only Hint: ❌ | Open World Hint: ✅