Post to Google Chat from an agent

The gchat_post_message tool posts a message to a Google Chat space, optionally with rich link cards, authenticated as a Chat app. Use it for proactive notifications, scheduled reports, and task updates, rather than only replying when the agent is mentioned.

Before you begin

The tool authenticates as a Google Chat app using a service account, so:

• The service account must be configured as a Google Chat app, and the Google Chat API must be enabled for its Google Cloud project.
• The Chat app must already be a member of the target space. There is no API to join a space, so a person has to add the app to the space, or the app must have created it. Posting to a space the app does not belong to fails.

Posting uses the https://www.googleapis.com/auth/chat.bot scope, which the app grants itself. No Google Workspace administrator approval is required for posting.

Credentials

The tool takes its credentials from one of two places, and the agent never sees them: both are filled by configuration, not chosen by the model.

A gchat_service_account_key agent secret. Store the full service account JSON key under that name and the tool picks it up automatically. No connector is needed.

STORE A GOOGLE CHAT SERVICE ACCOUNT KEY

Code example with bash syntax.bash

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An attached Google Chat connector. A connector of type gchat carries the same service account key and also lets the agent receive Chat events. Create one with the service account JSON key:

CREATE A GOOGLE CHAT CONNECTOR

Code example with bash syntax.bash

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The service account key is encrypted at rest and never returned. The read view of the connector returns client_email and project_id, parsed out of the key, plus an audience_url. To receive inbound events, set the Chat app's HTTP endpoint URL and Authentication audience to that audience_url in the Google Cloud console: inbound Google Chat ID tokens are accepted only when their aud matches it.

Credential precedence

When the tool runs, credentials resolve in this order:

1. An explicit service account key argument. The shipped configuration fills this from the gchat_service_account_key agent secret.
2. An explicit connector ID argument. The shipped configuration fills this from session.metadata.connector_id, which the connector sets on sessions it triggers. A connector ID that resolves to a non-Google connector (a Slack-triggered session cross-posting to Chat, for example) falls through to the steps below; one that resolves to nothing is an error.
3. The connector that triggered the current loop, if it carries Google credentials.
4. The first Google connector attached to the agent, ordered by connector ID.

If none of these produce credentials, the tool call fails with an error naming the gchat_service_account_key secret.

gchat_post_message

Posts a message to a space or thread.

Parameters

Parameter	Type	Required	Description
space_name	string	Yes	The resource name of the space, such as spaces/AAAAAqas8kM. This is not the space's display name.
text	string	Required unless cards is set	The message text, 1 to 32,000 characters.
cards	array	Required unless text is set	Rich cards appended below the message text.
thread_name	string	No	The resource name of an existing thread to reply in, such as spaces/AAAAAqas8kM/threads/UWknXX-lIB4. Omit to start a new thread.

A message with neither text nor cards is rejected before any request is sent. The whole message, text plus cards, is limited to 32,000 bytes.

Message text uses Google Chat text formatting: *bold*, _italic_, ~strikethrough~, `code`, ```code blocks```, <https://example.com|link text> links, and <users/USER_ID> mentions. Use <users/all> to mention everyone.

Response

Field	Type	Description
ok	boolean	Whether the message was posted. Always present.
message_name	string	The resource name of the posted message, such as spaces/AAAAAqas8kM/messages/UWknXX-lIB4.UWknXX-lIB4.
thread_name	string	The resource name of the message's thread.
error	string	The error message when the post failed.

When the Chat API rejects the post, the tool returns ok: false with error set, rather than failing the agent's turn.

Threading

Pass the thread_name returned by an earlier post, or observed on an incoming message, to reply in that thread. If the thread does not exist, the post fails instead of silently starting a new one. Spaces that do not use threading, such as direct messages and group chats, ignore thread_name.

Cards

Each entry in cards renders as a framed panel below the message text, with an optional header and one or more sections. Cards suit content with links the user should open: reports, alerts, and digests.

Field	Type	Required	Description
title	string	No	Card header title, rendered at the top of the card.
subtitle	string	No	Card header subtitle. Ignored unless title is set.
sections	array	Yes	The card body, rendered top to bottom. At least one section.

Each section takes an optional header, a text body, and a list of links, and must have text, links, or both. Sections are separated by a divider.

Field	Type	Required	Description
header	string	No	A small heading above the section content.
text	string	Required unless links is set	Section body text.
links	array	Required unless text is set	Link buttons rendered in a row below the section text.

Each link is a button with a text label and a url, which must be http or https. Clicking it opens the URL in the user's browser, so no card interactivity support is needed in the Chat app.

Section text uses HTML-style formatting rather than Chat text markup: <b>bold</b>, <i>italic</i>, <s>strikethrough</s>, <u>underline</u>, <a href="https://example.com">inline links</a>, and <br> for line breaks.

{
  "space_name": "spaces/AAAAAqas8kM",
  "text": "*Nightly index run finished.*",
  "cards": [
    {
      "title": "Index run 4821",
      "subtitle": "Completed in 12m",
      "sections": [
        {
          "header": "Summary",
          "text": "<b>18,204</b> documents indexed, <b>3</b> failures.",
          "links": [
            { "text": "Open report", "url": "https://example.com/runs/4821" }
          ]
        }
      ]
    }
  ]
}

Chat-triggered agents

When a Google Chat connector triggers an agent, the connector already posts the agent's final reply to the triggering space and thread. An agent that also calls gchat_post_message with the same content posts the message twice. Instruct such agents to use the tool only for messages beyond the final reply: posts to other spaces or threads, and mid-run progress updates.

Related guides

• Slack connectors
• Agent secrets
• Connector authentication patterns
• Agent tools
• Create agent connector API