Composing emails
The block model
Emit content as an array of { tag, content } blocks. Only three tags exist:
- paragraph →
<p>body copy - heading →
<h2>section header - link →
<a>for URLs
No lists, tables, images, bold/italic, blockquotes, or code blocks. If you need emphasis, use a heading + paragraph. If you need a list, write each item as its own paragraph. All strings are HTML-escaped, so don't try to inject tags.
Formatting rules
- No markdown. No
#headings, no**bold**, no-bullets — they render literally. - No newlines inside a block's
content— break into separate blocks instead. - Preserve URLs from source data as
linkblocks, not inline in paragraph text. - Format numbers, prices, and dates clearly inside paragraph copy (e.g.
$1,234.56,April 28, 2026).
Tone
- Professional but friendly
- Descriptive subject line — not "Update" or "FYI"
- Lead with the point; don't bury it under context
- One idea per paragraph
Recipient sourcing
Always read the recipient address from a typed signal-payload field interpolated into the action prompt — never from upstream agent output. LLM agents will confabulate plausible-looking addresses when the field is absent rather than failing.
Wire it end-to-end:
-
Signal schema declares the recipient as a
requiredfield — caller can't trigger the job without it.yamlsignals: send-alert: schema: type: object properties: notify_email: { type: string, format: email } required: [notify_email] -
Action prompt interpolates from the signal payload (works in any step, including ones with
inputFrom— seewriting-workspace-jobs→ "Signal payload threading"):yaml- type: agent agentId: emailer prompt: "Send the alert to {{inputs.notify_email}}" -
Email-sender agent system prompt should refuse rather than guess: "If the recipient address contains an unresolved
{{...}}placeholder or is missing, callfailStepwith a reason. Never invent a recipient."
The literal-placeholder check is the important part — the FSM engine intentionally leaves unresolved placeholders verbatim so authoring bugs stay visible. A guarded agent treats that as a hard stop.
