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resend

Email Sending MCP

by resend

Send Email

send-email

Send a single transactional email to one or more recipients instantly or schedule it for later. Ideal for notifications, confirmations, and direct replies.

Instructions

Purpose: Send a single transactional email to one or more recipients immediately (or schedule it). Use for one-off messages, notifications, and direct replies.

NOT for: Sending the same email to a whole list/audience (use create-broadcast + send-broadcast). Not for managing contacts or audiences.

Returns: Send confirmation and email ID.

When to use:

  • User wants to "send an email" to specific people (names or addresses)

  • One-off messages: password reset, order confirmation, receipt, alert

  • User says "email this to X", "notify them", "send a message to..."

  • Scheduling a single email for later

Workflow: Get recipient(s) and content from user → send-email. Use list-emails or get-email to check delivery status afterward.

Key trigger phrases: "Send an email", "Email this to", "Notify", "Send a message", "Reply to them", "Schedule an email"

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
ccNoOptional array of CC email addresses. You MUST ask the user for this parameter. Under no circumstance provide it yourself
toYesArray of recipient email addresses (1-50 recipients)
bccNoOptional array of BCC email addresses. You MUST ask the user for this parameter. Under no circumstance provide it yourself
fromYesSender email address. You MUST ask the user for this parameter. Under no circumstance provide it yourself
htmlNoHTML email content. When provided, the plain text argument MUST be provided as well.
tagsNoArray of custom tags for tracking/analytics. Each tag has a name and value.
textYesPlain text email content
replyToNoOptional email addresses for the email readers to reply to. You MUST ask the user for this parameter. Under no circumstance provide it yourself
subjectYesEmail subject line
topicIdNoTopic ID for subscription-based sending. When set, the email respects contact subscription preferences for this topic.
attachmentsNoArray of file attachments. Each needs filename plus one of: filePath, url, or content. Max 40MB total.
scheduledAtNoOptional parameter to schedule the email. This uses natural language. Examples would be 'tomorrow at 10am' or 'in 2 hours' or 'next day at 9am PST' or 'Friday at 3pm ET'.
Behavior4/5

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

With no annotations, the description carries full burden. It describes immediate/scheduled sending, return value (confirmation and email ID), and attachment size limit via schema. However, it omits potential costs, idempotency, or error behavior, which are useful for an agent.

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?

Well-structured with sections and bullet points, front-loaded. Slightly verbose with trigger phrases and workflow step, but these add value. Could be trimmed slightly without loss.

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 12 params, 4 required, no output schema, and many siblings, the description covers purpose, exclusions, examples, workflow, and trigger phrases. Lacks details on output format or error states, but adequate for most use cases.

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 coverage is 100%, so baseline 3. The description does not add meaning beyond the schema's detailed parameter descriptions. It repeats no schema info, but also adds no extra semantics.

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

Purpose5/5

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

The description clearly states it sends a single transactional email to one or more recipients, immediately or scheduled. It contrasts with broadcast tools, making the purpose unambiguous.

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

Usage Guidelines5/5

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

Explicitly states when to use (one-off messages, notifications, direct replies) and when not to (use create-broadcast + send-broadcast for list sends). Includes trigger phrases and workflow links.

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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