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Email Sending MCP

by resend

Create Broadcast

create-broadcast

Create a broadcast campaign to send one email to an entire segment. Define subject, body, and segment; returns a broadcast ID for later sending.

Instructions

Purpose: Create a broadcast campaign (one email sent to an entire segment). Defines subject, body, and segment; does NOT send yet. Use send-broadcast to send it.

NOT for: Sending a one-off email to specific people (use send-email). Not for adding contacts (use create-contact).

Returns: Broadcast ID. Use this ID with send-broadcast to send, or get-broadcast/update-broadcast to manage.

When to use:

  • User wants to "email my list", "send a newsletter", "broadcast to my segment", "email all contacts in X"

  • Newsletter, announcement, or bulk message to one segment

  • Supports personalization: {{{FIRST_NAME}}}, {{{LAST_NAME}}}, {{{EMAIL}}}, {{{RESEND_UNSUBSCRIBE_URL}}}

"All contacts" note: Broadcasts require a segment. There is no "all contacts" option in the API. If the user wants to send to all contacts, check list-segments for an existing segment that covers everyone. If none exists, suggest creating one with create-segment.

Workflow: list-segments (if needed) → create-broadcast → get-tiptap-json-content (with include_schema: true) → compose-broadcast → send-broadcast.

Content options after creating:

  • compose-broadcast (recommended): Sets TipTap content that the user can visually edit in the Resend dashboard. Use this when the user wants to collaborate on or refine the email in the editor.

  • update-broadcast with html/text: Sets static HTML/text content. Use this only when the user explicitly wants to set raw HTML. Switching between compose and html/text modes is lossy — some content or formatting may be lost. Ask the user before switching.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
fromYesFrom email address (e.g. "onboarding@resend.com" or "Resend <onboarding@resend.com>")
htmlNoHTML version of the email content. Placeholders: {{{FIRST_NAME|fallback}}}, {{{LAST_NAME|fallback}}}, {{{EMAIL}}}, {{{RESEND_UNSUBSCRIBE_URL}}}. Email HTML requirements — follow all of these without exception: STRUCTURE - Always include <!DOCTYPE html>, <html>, <head>, <body> - Layout must be table-based: <table>, <tr>, <td> — never use <div> for layout - Outer wrapper table at width="100%", inner content table at max 600px wide - Every table must have cellpadding="0" cellspacing="0" border="0" CSS - All styles must be inline (style="...") — no <style> tag, no external stylesheets - No flexbox, no grid, no CSS variables, no CSS shorthand (use padding-top not padding) - font-family must always include web-safe fallbacks (Arial, Helvetica, Georgia, sans-serif) - Always set font-size, line-height, and color explicitly on every text element IMAGES - Always set width, height, border="0", display:block on every <img> - Use absolute URLs only — no relative paths - Always include alt text LINKS & BUTTONS - Never use <button> — use <a> styled as a button inside a <td> - No <video>, <form>, or <input> elements - No JavaScript of any kind OUTLOOK COMPATIBILITY - Use bgcolor attribute on <td> alongside CSS background-color - No CSS background-image (poor Outlook support) - Add <!--[if mso]> conditionals where needed for Outlook rendering META (in <head>) - <meta charset="UTF-8"> - <meta name="viewport" content="width=device-width, initial-scale=1.0"> - <meta http-equiv="X-UA-Compatible" content="IE=edge">
nameYesName for the broadcast. If the user does not provide a name, go ahead and create a descriptive name for them, based on the email subject/content and the context of your conversation.
textYesPlain text version of the email content. The following placeholders may be used to personalize the email content: {{{FIRST_NAME|fallback}}}, {{{LAST_NAME|fallback}}}, {{{EMAIL}}}, {{{RESEND_UNSUBSCRIBE_URL}}}
replyToNoReply-to email address(es)
subjectYesEmail subject
segmentIdYesSegment ID to send to
previewTextNoPreview text for the email
Behavior4/5

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

With no annotations, the description carries full burden. It discloses that the tool only creates but does not send, returns a Broadcast ID, and warns about lossy mode switches. Could add permission or rate limit info, but overall provides key behavioral context.

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 headings, front-loaded purpose, and logical flow. Slightly longer than minimal but every sentence adds value. No redundancy.

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

Completeness5/5

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

Covers return value, required workflow, edge cases (no 'all contacts' segment), and content mode decisions. Without an output schema, the description fully explains what the tool produces and how it fits into broader processes.

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 baseline is 3. The description adds no additional parameter-level meaning beyond what the schema already provides, though it contextualizes the tool's role.

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 explicitly states the verb 'Create', the resource 'broadcast', and clarifies that it does NOT send the broadcast. It distinguishes from sibling tools like send-broadcast, send-email, and create-contact, making selection clear.

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?

Provides explicit 'When to use' examples and 'NOT for' cases with alternative tools. Includes a full workflow from list-segments to send-broadcast, and discusses when to use compose-broadcast vs update-broadcast with trade-offs.

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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