GMAIL tools: support multiple attachments (attachment field is singular object, not array)

[ibbybuilds]

Problem

All Gmail tools that accept file attachments (GMAIL_SEND_EMAIL, GMAIL_CREATE_EMAIL_DRAFT, GMAIL_REPLY_TO_THREAD) define the attachment parameter as a single object:

"attachment": {
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "mimetype": { "type": "string" },
    "s3key": { "type": "string" }
  }
}

This means users can only attach one file per email. There is no way to send an email with multiple attachments — a very common real-world need.

The Gmail API itself has zero limitation here — RFC 2822 MIME multipart/mixed supports unlimited attachment parts (up to the 25MB total size limit).

Requested Change

Add an attachments field (array of file objects) to all Gmail tools that accept files:

"attachments": {
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "name": { "type": "string" },
      "mimetype": { "type": "string" },
      "s3key": { "type": "string" }
    }
  }
}

Affected tools:

• GMAIL_SEND_EMAIL
• GMAIL_CREATE_EMAIL_DRAFT
• GMAIL_REPLY_TO_THREAD

Also missing:

• GMAIL_UPDATE_DRAFT — there is no tool to update an existing draft. This would be useful for incrementally building emails with multiple attachments, or editing drafts before sending.

Context

• This was previously reported in Discussion Support sending multiple attachements for `GMAIL_SEND_EMAIL` #1970 (Sep 2025) with no resolution
• Issue Can't send attachments with GMAIL_SEND_EMAIL #1905 confirmed single-attachment is the current intended behavior
• We're building an AI agent platform (open source) that uses Composio's composio-client REST API for Gmail/Drive/etc integrations. Multiple attachments is a frequently requested user need that we currently cannot fulfill.

Workaround Attempted

We considered creating a draft with attachment A, then updating with attachment B — but drafts.update in Gmail API is a full PUT (replaces entire message), so previous attachments are lost. And the singular attachment field means we can't pass [A, B] anyway.

The only current workaround is using the proxy tool to construct raw MIME messages, which defeats the purpose of having high-level tool abstractions.

[Uday-sidagana]

Hey @ibbybuilds, Currently, we do not have support for multiple attachments. We will add it to our roadmap.

[Eddydpyl]

+1 this is pretty essential. right now we're having to zip files, which is not ideal.