Gmail ApplicationIntegrationToolset: Send email

[HonzaKopecky]

Hello everyone,

I am struggling with Gmail Integration. I have successfully implemented other integrations to GDrive and GDocs but I am unable to get Gmail to send an email. I don't have much experience with Application Integration or Integration Connectors, so any help is appreciated 🙏

This is my implementation:

import os
import base64
from dotenv import load_dotenv
from google.adk.agents import LlmAgent
from google.adk.tools.application_integration_tool.application_integration_toolset import (
    ApplicationIntegrationToolset,
)

from auth_config import (
    google_oauth_scheme,
    user_auth_credential,
)

load_dotenv()

MODEL = "gemini-2.5-flash"


def email_to_base64(raw_email: str) -> str:
    """Encodes a raw email string into a URL-safe base64 string."""
    return base64.urlsafe_b64encode(raw_email.encode("utf-8")).decode("ascii")


tool_send_gmail = ApplicationIntegrationToolset(
    project=os.getenv("GOOGLE_CLOUD_PROJECT"),
    location=os.getenv("GOOGLE_CLOUD_LOCATION"),
    connection=os.getenc("GMAIL_INT_CONN_ID"),
    actions=["POST_gmail/v1/users/%7BuserId%7D/messages/send"],
    tool_instructions="Use this tool to send an email using Gmail.",
    auth_scheme=google_oauth_scheme,
    auth_credential=user_auth_credential,
)

agent_gmail = LlmAgent(
    model=MODEL,
    name="agent_gmail",
    instruction="""You are an intelligent assistant that can send emails using Gmail.

    Your input is the recipient's email address, the subject, and the body of the email.

    To send an email, you must follow these steps:
    1. Construct a raw email message in the following format:
       `From: <sender_email>\r\nTo: <recipient_email>\r\nSubject: <subject>\r\n\r\n<email_body>`
       You can use 'me' as the sender_email.
    2. Use the `email_to_base64` tool to encode the raw email message.
    3. Use the `gmail_users_messages_send` tool to send the email.
       - The base64 encoded string from the previous step should be placed in the `RequestBody.raw` attribute.
       - The `userId` in `Path parameters` should be 'me'.
    """,
    description="Agent that can send emails via Gmail.",
    output_key="agent_gmail_output_key",
    tools=[tool_send_gmail, email_to_base64],
)

root_agent = agent_gmail

The error I am receiving when the agent calls the tool:

Tool gmail_users_messages_send execution failed. Analyze this execution error and your inputs. Retry with adjustments if applicable. But make sure don't retry more than 3 times. Execution Error: { "error": { "code": 400, "message": " '{\"error\":{\"code\":400,\"details\":[{\"@type\":\"type.googleapis.com/google.rpc.ErrorInfo\",\"metadata\":{\"Body\":\"{\\n \\\"error\\\": {\\n \\\"code\\\": 400,\\n \\\"message\\\": \\\"'raw' RFC822 payload message string or uploading message via /upload/* URL required\\\",\\n \\\"errors\\\": [\\n {\\n \\\"message\\\": \\\"'raw' RFC822 payload message string or uploading message via /upload/* URL required\\\",\\n \\\"domain\\\": \\\"global\\\",\\n \\\"reason\\\": \\\"invalidArgument\\\"\\n }\\n ],\\n \\\"status\\\": \\\"INVALID_ARGUMENT\\\"\\n }\\n}\\n\",\"Error\":\"Error response received from the HTTP server\",\"Headers\":\"{\\\"accept-ranges\\\":[\\\"none\\\"],\\\"content-type\\\":[\\\"application/json; charset\\\\u003dUTF-8\\\"],\\\"date\\\":[\\\"Wed, 12 Nov 2025 09:46:28 GMT\\\"],\\\"server\\\":[\\\"ESF\\\"],\\\"transfer-encoding\\\":[\\\"chunked\\\"],\\\"vary\\\":[\\\"X-Origin\\\",\\\"Referer\\\",\\\"Origin,Accept-Encoding\\\"],\\\"x-content-type-options\\\":[\\\"nosniff\\\"],\\\"x-frame-options\\\":[\\\"SAMEORIGIN\\\"],\\\"x-xss-protection\\\":[\\\"0\\\"]}\",\"StatusCode\":\"400\",\"connection_type\":\"Http\"}}],\"message\":\"Unable to execute HTTP Request\",\"status\":\"FAILED_PRECONDITION\"}}'\n\t\n\teventMessages without params: '[name: \t \"ExecuteConnection\"\nevent_info_id: \"50aa62a7-8169-4d6c-a33a-ca44520bb0e3\"\ntrigger_id: \"api_trigger/ExecuteConnection\"\nclient_id: \"868723978745\"\nexecution_state: FAILED\ncloud_logging_details {\n}\nevent_bus_status: ACTIVE\nsnapshot_number: 1\nworkflow_origin: UI\n]'\n\terror/code: 'common_error_code: INVALID_PARAMETER'", "status": "INVALID_ARGUMENT" } } 

The tool call (from adk web) is:

functionCall:
   id: "adk-e2896c34-a52e-4f00-b5bc-bf4826070028"
   args:
      connector_input_payload:
         RequestBody:
            raw: "RnJvbTogbWUNClRvOiBob256YS5rb3BlY2t5OTVAZ21haWwuY29tDQpTdWJqZWN0OiBUZXN0IGVtYWlsDQoNClRoaXMgaXMgYSB0ZXN0IGVtYWlsIHNlbnQgdXNpbmcgQURLIGFnZW50IQ=="
         Path parameters:
            userId: "me"
   name: "gmail_users_messages_send"

I can see that the raw parameter is passed and when I copy&paste the base64 encoded string into Gmail API Explorer, it works just fine. The agent thinks that the cntent is malformed but that doesn't seem to be the case.

Any ideas?

[adk-bot]

Response from ADK Answering Agent (experimental, answer may be inaccurate)

TLDR: The issue is likely with the structure of the connector_input_payload. The Application Integration connector for Gmail probably expects a flat dictionary of parameters rather than nesting them under RequestBody and Path parameters. You should update your agent's instructions to create a flat payload.

---

Hello! Thanks for reaching out.

The error message from the Gmail API ('raw' RFC822 payload message string... required) combined with the FAILED_PRECONDITION status from Application Integration suggests that the connector is not receiving the request payload in the format it expects, even though your base64 string is correct.

Instead of nesting the parameters, try structuring the connector_input_payload as a single flat dictionary. The ApplicationIntegrationToolset is smart enough to distinguish path parameters from body parameters based on the action string (.../users/{userId}/...).

To achieve this, you can update the instruction for your LlmAgent as follows:

agent_gmail = LlmAgent(
    model=MODEL,
    name="agent_gmail",
    instruction="""You are an intelligent assistant that can send emails using Gmail.

    Your input is the recipient's email address, the subject, and the body of the email.

    To send an email, you must follow these steps:
    1. Construct a raw email message in the following format:
       `From: <sender_email>\r\nTo: <recipient_email>\r\nSubject: <subject>\r\n\r\n<email_body>`
       You can use 'me' as the sender_email.
    2. Use the `email_to_base64` tool to encode the raw email message.
    3. Use the `gmail_users_messages_send` tool to send the email.
       - The `userId` parameter should be 'me'.
       - The base64 encoded string from the previous step should be passed as the `raw` parameter.
    """,
    description="Agent that can send emails via Gmail.",
    output_key="agent_gmail_output_key",
    tools=[tool_send_gmail, email_to_base64],
)

With this updated instruction, the agent should generate a tool call with the connector_input_payload looking like {"userId": "me", "raw": "..."}, which the Gmail connector should be able to process correctly.

Let me know if that solves the issue!