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marius-cetanas

macos-mail-mcp

by marius-cetanas
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TypeScript
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reply_to_message

Reply to an existing email message using its ID and mailbox, returning the sender address. Attachments are not supported.

Instructions

Reply to an existing email message. Returns the sender the reply was sent from. Does not support attachments (Mail.app limitation).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
bodyYesThe reply body text
replyAllYesWhether to reply to all recipients (true) or just the sender (false)
messageIdYesThe numeric ID of the message to reply to
accountNameYesThe name of the account containing the mailbox. This locates the source message only — it does not control which account sends. Use fromAccount for that.
fromAccountNoAccount to send from — a Mail account name ("Google") or one of its addresses ("you@gmail.com"), as reported by list_accounts. Matching is case-insensitive and an unrecognised value is an error, never a silent fallback. Omit to use Mail's default sending account; either way the account used is returned as `sender`.
mailboxNameYesThe name of the mailbox containing the message

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv1.3.2
    • removedInput schema / additionalProperties
      Removed value: -false
    • changedInput schema / properties / accountName / description
      Previous value: -"The name of the account containing the mailbox"New value: +"The name of the account containing the mailbox. This locates the source message only — it does not control which account sends. Use fromAccount for that."
    • addedInput schema / properties / fromAccount
      Added value: +{
+  "description": "Account to send from — a Mail account name (\"Google\") or one of its addresses (\"you@gmail.com\"), as reported by list_accounts. Matching is case-insensitive and an unrecognised value is an error, never a silent fallback. Omit to use Mail's default sending account; either way the account used is returned as `sender`.",
+  "type": "string"
+}
    • addedInput schema / properties / messageId / maximum
      Added value: +9007199254740991
    • addedInput schema / properties / messageId / minimum
      Added value: +-9007199254740991
  2. First observedv1.2.0

TDQS

A3.6/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the burden of behavior disclosure. It does disclose the returned value ('sender') and the unsupported attachment behavior, but it does not explicitly state that this sends a message as a side effect or describe the reply content/thread behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two compact sentences with high information density: the core action, the key return value, and the attachment limitation. There is no filler or redundant restating of the tool name.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The schema already covers all six parameters, and the description adds the most decision-relevant behavioral facts. It stops just short of fully complete because it does not outline the full return structure or emphasize the potentially irreversible sending side effect, and there is no output schema to fill that gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the parameters are already well documented in the input schema. The description adds no additional parameter-level semantics, so the baseline of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: 'Reply to an existing email message.' It clearly distinguishes the tool from sending a new message or forwarding by the word 'Reply' and by referencing an existing message, though it does not name sibling tools explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied rather than explicit: it is for replying to an existing email. It also calls out a meaningful limitation, 'Does not support attachments (Mail.app limitation),' but does not explicitly say when to choose send_message or forward_message instead.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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