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Email Sending MCP

by resend

Update Broadcast

update-broadcast

Update broadcast metadata such as name, subject, sender, and content by providing broadcast ID or Resend dashboard URL. Ensure from address and segment ID are included if missing.

Instructions

Update broadcast metadata by ID or Resend dashboard URL (name, subject, from, html, text, segment, preview text, reply-to). To edit TipTap content, use compose-broadcast instead.

Important: The API requires from and segmentId to be set on the broadcast. If the broadcast was created from the dashboard, these may be empty. Always call get-broadcast first to check, and include from and segmentId in your update if they are not already set. Use list-domains to find verified domains for the from address, and list-segments to find segment IDs.

Note on html/text fields: Setting html or text via this tool replaces any content previously set via compose-broadcast. This switch is lossy — some content or formatting may be lost. Prefer compose-broadcast for content changes. If the broadcast was composed with TipTap content, ask the user before overwriting it with raw HTML.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
fromNoFrom email address (e.g. "onboarding@resend.com" or "Resend <onboarding@resend.com>")
htmlNoHTML content of the email. 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">
nameNoName for the broadcast
textNoPlain text content of the email
replyToNoReply-to email address(es)
subjectNoEmail subject
segmentIdNoSegment ID to send to
broadcastIdYesBroadcast ID or Resend dashboard URL (e.g. https://resend.com/broadcasts/<id>)
previewTextNoPreview text for the email
Behavior5/5

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

Discloses that setting html/text via this tool is lossy and can overwrite TipTap content. Recommends asking user before overwriting and preferring compose-broadcast for content changes. No annotations were provided, so description fully compensates.

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?

Front-loaded with clear purpose and alternative tool, followed by important usage notes. Well-structured with paragraphs and bold for key terms. No unnecessary sentences.

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?

Given 9 parameters, no output schema, and many siblings, the description is comprehensive: covers purpose, usage, side effects, prerequisites, and cross-references. No gaps identified.

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

Parameters5/5

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

Schema coverage is 100%, but description adds significant meaning beyond schemas: explains that broadcastId can be a URL, that from and segmentId may be required if empty, and that html/text replacement is lossy. Provides concrete usage advice.

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?

Clearly states the verb 'update', the resource 'broadcast metadata', and lists specific fields. Distinguishes from sibling 'compose-broadcast' by explicitly stating when to use that tool instead.

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 guidance, prerequisites (check get-broadcast for from/segmentId), and cross-references to other tools (list-domains, list-segments). Gives clear alternatives for content changes.

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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