Mailercloud

send_transactional_email

Destructive

Send a transactional email via MailerCloud Email API. Supports HTML, AMP HTML, attachments, CC/BCC. Use version 1.0 for HTML only, 2.0 for AMP content. Two steps: call first WITHOUT confirm (or confirm: false) to get a preview (recipient count, from, subject) — nothing is sent. Show the preview to the user and get an explicit yes, then call again with confirm: true to send. dry_run: true returns the preview without sending even when confirm is true.

Input Schema

Name	Required	Description
`cc`	No	CC recipients
`to`	Yes	To recipients (array of name and email)
`bcc`	No	BCC recipients
`from`	Yes	Sender email address
`html`	No	HTML content
`text`	No	Plain text content
`confirm`	No	Must be true to actually send. Leave false first to get a preview of recipients, sender and subject
`dry_run`	No	Validate and show the send preview without sending, even when confirm is true
`subject`	Yes	Email subject
`version`	No	API version - 1.0 for HTML or 2.0 for AMP
`amp_html`	No	AMP HTML content
`reply_to`	No	Reply-to addresses
`from_name`	No	Sender display name
`attachments`	No	Attachments (array of name and url)

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedOct 23, 2026

changedInput schema / properties / from / description

Previous value: -"Sender email address,required"New value: +"Sender email address"

changedInput schema / properties / subject / description

Previous value: -"Email subject,required"New value: +"Email subject"

changedInput schema / properties / to / description

Previous value: -"To recipients (array of name and email),required"New value: +"To recipients (array of name and email)"

Changed3 schema fields changedOct 19, 2026

removedInput schema / properties / api_key

Removed value: -{
-  "description": "MailerCloud API key",
-  "type": "string"
-}

addedInput schema / properties / confirm

Added value: +{
+  "description": "Must be true to actually send. Leave false first to get a preview of recipients, sender and subject",
+  "type": "boolean"
+}

addedInput schema / properties / dry_run

Added value: +{
+  "description": "Validate and show the send preview without sending, even when confirm is true",
+  "type": "boolean"
+}

First observedSep 2, 2026

TDQS

A4.1/5.0

Behavior5/5

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

Annotations already mark the tool as destructive and open-world, and the description adds critical safety context: nothing is sent without confirm, previews show recipient count/from/subject, and dry_run prevents sending even when confirm is true. This fully discloses the risky two-step send 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 front-loaded with purpose and features, then explains the two-step confirmation flow and dry_run in a compact sequence. Every sentence contributes useful information without waste.

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 14 parameters, no output schema, and destructive annotations, the description covers the essential preview-confirm safety workflow and feature support. It does not address authentication or sender verification requirements, but those are secondary for correct invocation.

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 schema already documents all 14 parameters including confirm, dry_run, and version. The description mostly repeats those semantics rather than adding new constraints, so baseline 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?

States a specific verb and resource ('Send a transactional email via MailerCloud Email API') and lists supported features. It does not explicitly differentiate from sibling tools like send_personalized_email or send_test_email, so sibling differentiation is missing.

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?

Provides clear operational guidance: use version 1.0 for HTML and 2.0 for AMP, call first without confirm to preview, get explicit user approval, then confirm to send; dry_run also previews. It does not say when to choose this tool versus alternatives such as send_personalized_email.

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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