How to use the Gmail Reply Sender agent skill

What is an agent skill, and what does this one do?

An agent skill is a folder containing a SKILL.md file that teaches an AI agent how to perform a specific task with a tool. This skill covers one task: replying to a Gmail message. The agent supplies a message ID and the reply text, and the skill sends the reply through the gws command-line tool.

The reply is threaded correctly under the original conversation, and the original message is quoted in the reply body. The skill only handles replies. Sending a brand-new email requires the general gmail skill.

• Replies stay in the same Gmail thread.
• The original message is quoted in the reply.
• Extra recipients (To, CC, BCC) can be added.
• Files can be attached, and HTML formatting can be used.
• A reply can be saved as a draft instead of being sent.

How do you install the gws-gmail-reply skill?

There are two ways to install the skill. For Claude Code, download the ZIP from this page and unzip it into ~/.claude/skills/ to make it available for all your projects. To limit it to one project, unzip it into the .claude/skills/ folder inside that project.

In the Claude apps, you can instead upload the ZIP under Settings → Capabilities → Skills.

• Personal install: ~/.claude/skills/
• Project install: .claude/skills/ inside your project folder
• Claude apps: Settings → Capabilities → Skills, then upload the ZIP

What do you need before the skill works?

The skill needs three things: the gws command-line tool (the googleworkspace CLI), Google Workspace authentication configured through gws, and the Gmail message ID of the message you want to reply to. The skill's SKILL.md points to a gws-shared skill for authentication, global flags and security rules. If that file is missing, the source says to run gws generate-skills to create it.

• The gws command-line tool must be installed and available as gws.
• Authentication must be configured via gws (see the gws-shared skill).
• You need the Gmail message ID of the message to reply to.

How do you trigger the skill with a natural request?

You do not need to type the command yourself. Ask the agent in plain language and include the message ID and the reply text. The agent uses the skill to build the command. Because a reply goes to real people, ask the agent to save it as a draft if you want to review it first.

The underlying command takes the message ID and the body. Other flags are optional.

• "Reply to Gmail message 18f1a2b3c4d saying thanks, got it."
• "Reply to message 18f1a2b3c4d with 'Updated version attached' and attach updated.docx."
• "Save a draft reply to message 18f1a2b3c4d that says 'Draft reply' so I can check it."

What flags can the agent use?

The skill documents these flags. Only --message-id and --body are required. --dry-run shows the request that would be sent without executing it, which is useful for checking before anything goes out.

--from sets the sender address for send-as or alias accounts. Leave it out to use the account default. --to adds extra To recipients, --cc and --bcc add copies, and --attach (or -a) adds a file and can be repeated. --html treats the body as HTML instead of plain text. --draft saves the reply instead of sending it.

• --message-id (required): Gmail message ID to reply to
• --body (required): reply text, plain or HTML with --html
• --from: sender address for send-as/alias
• --to, --cc, --bcc: comma-separated addresses
• --attach / -a: file attachment, can be repeated
• --html: treat --body as HTML
• --dry-run: show the request without executing it
• --draft: save as draft instead of sending

What do the examples look like?

The skill includes these examples. Each uses the same message ID so you can see how the optional flags change the result.

• Simple reply: gws gmail +reply --message-id 18f1a2b3c4d --body 'Thanks, got it!'
• Add a CC: --cc carol@example.com
• Add a To recipient: --to dave@example.com
• HTML reply: --body '<b>Bold reply</b>' --html
• Attachment: -a updated.docx
• Save as draft: --draft

What safety points should you know?

This skill runs scripts and uses the network. It sends mail through your Google account, so it can act on your behalf. Replies go to real people and cannot be recalled once sent. Review the request first with --dry-run or save the reply with --draft, especially for unattended runs.

The skill is not meant for replying to all recipients automatically. For that, the source points to a separate +reply-all command. The skill also does not reply-all by itself.

• It runs scripts and uses the network.
• Replies cannot be recalled once sent.
• Use --dry-run to inspect the request, or --draft to review in Gmail.
• Do not use it for unattended sending without review.
• Use +reply-all for reply-all.

What tips help you get better results?

The skill sets the In-Reply-To, References and threadId headers for you, so you do not need to manage threading. When you use --html, the quoted block keeps Gmail's gmail_quote styling and inline images in the quoted message are preserved. Use fragment tags such as <p>, <b> and <a>. A full <html> or <body> wrapper is not needed.

• Threading headers are set automatically.
• Use fragment tags (<p>, <b>, <a>) with --html; no <html>/<body> wrapper is needed.
• Inline images in the quoted message are kept when using --html.
• Use --draft while you are learning the skill.