MCP Emails

Set Signature

signature_set

Idempotent

Set or update an email signature for an inbox using plain text or HTML, with controls for enabling/disabling, reply behavior, and clearing the signature entirely.

Instructions

Set or update the email signature for an inbox. Provide the signature as signature_text (plain text) and/or signature_html (rich HTML) — pass either or both; the missing half is derived automatically on send. Pass an empty string for both to clear the signature. Optionally set signature_enabled (default true; set false to stop appending without deleting the text) and signature_reply_mode ('always' = sign every reply/forward, 'first_only' = only the first message in a thread, 'never' = never sign replies/forwards). Setting a signature marks its source as 'manual', which permanently overrides Gmail auto-import for that inbox. sender_name sets the display name recipients see in the From header, e.g. "Evancoe Bot bot@evancoe.com"; it can be set on its own without touching the signature.

Input Schema

TableJSON Schema

Name	Required	Description
`inbox`	No	Inbox email address, an alternative to inbox_id.
`inbox_id`	No	Inbox UUID from inbox_list. Optional when the key has one inbox; pass this or `inbox`, not both.
`sender_name`	No	Display name recipients see in the From header, e.g. 'Evancoe Bot' gives "Evancoe Bot <bot@evancoe.com>". Omit to keep, empty string to clear. Whitespace is collapsed; control characters and angle brackets are removed.
`signature_html`	No	HTML signature. Omit to keep, empty string to clear. Derived from the text version when only that is given.
`signature_text`	No	Plain-text signature. Omit to keep, empty string to clear.
`signature_enabled`	No	Whether the signature is appended at all. Defaults to true.
`signature_reply_mode`	No	Signature on replies and forwards; 'first_only' is the default.

Output Schema

TableJSON Schema

Name	Required	Description
`notes`	No	Server notes about how this call was handled — for example an argument that was not applied because the selected action does not accept it. Written by MCP Emails, not taken from any message, and absent when there is nothing to report.
`saved`	No
`inbox_id`	No
`sender_name`	No
`email_address`	No
`signature_enabled`	No
`signature_reply_mode`	No

Schema Changelog

Changes observed during successful MCP inspections.

AddedSep 10, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already mark readOnly=false and idempotent=true, and the description adds valuable non-obvious behavior: set signatures permanently override Gmail auto-import, the text and HTML forms are derived from each other, and disabling via signature_enabled preserves the stored content. This goes beyond the structured metadata, though it could also mention what happens when both signature_text and signature_html are omitted.

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

Conciseness4/5

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

The description is dense and front-loaded: the action is in the first sentence, and every subsequent clause adds operational detail. It is a single paragraph that covers many parameters without repetition, though it could be slightly reorganized by grouping the shape-change parameters separately from the enable/clear semantics.

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?

Given seven optional parameters and a high-coverage schema plus output schema, the description covers the critical context: defaults, clearing semantics, derivation rules, and the persistent side effect of overriding auto-import. The only minor gap is guidance on what happens if no inbox is specified or if no parameters are passed, which the schema leaves ambiguous.

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

Parameters4/5

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

The input schema already documents all seven parameters fully (>80% coverage), so the baseline is appropriate. The description still adds meaning by explaining cross-parameter relationships—'signature_text and signature_html ... you can provide either one and the other is derived'—and the clearing semantics of empty strings, which the schema alone does not convey.

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 opens with a specific verb+resource: 'Set or update the email signature for an inbox,' which clearly states what the tool does. It goes beyond the title by enumerating the controllable aspects (text, HTML, enabled flag, reply mode, sender name), but it does not explicitly distinguish itself from sibling tools such as email_compose or draft.

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

Usage Guidelines4/5

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

The description gives concrete usage conditions: pass empty strings to clear, set signature_enabled to false to disable without deleting text, and pass either or both text formats with the missing one derived. It explains the manual-override consequence of setting a signature. It does not name alternative tools to use instead, but the conditional usage is otherwise explicit.

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