Resend Send Native Node

Resend Send Native Node

Send email via the Resend.com HTTPS API.

Native Node.js. Zero dependencies. One POST call for real sends. Small enough to audit directly.

When to use

Trigger phrases: "email me", "send an email", "mail this to", "send a notification", "email the report".

Use this when:

• The user wants to send an email fast, without Gmail OAuth or App Password pain
• Simple "fire and forget" sends (no inbox reading needed)
• The user has a Resend.com account (check Resend's current pricing/limits before relying on a specific quota)
• Weekly/report-style outbound messages where the body is generated from explicitly reviewed text

Do NOT use this when:

• The user wants to READ email (this is send-only)
• The user needs to send from a specific personal Gmail address (use a Gmail-specific skill)
• Sensitive business emails where provenance matters (Resend's default onboarding@resend.dev sender looks transactional)
• The recipient, sender, or final body has not been explicitly reviewed/approved for a real send

Safety policy for agents

This skill is send-only, but it is still externally mutating. For agent use:

1. Draft first. Generate or inspect the exact body text before sending.
2. Dry-run first. The script dry-runs by default; review the printed payload.
3. Explicit approval. Use --send only after the user explicitly approves that exact recipient, subject, and body.
4. Use an allowlist. Real sends fail closed unless RESEND_ALLOWED_TO=addr@example.com,other@example.com is set in the process environment for approved recipients.
5. No raw memory dumps. Email only curated report text, not unfiltered memory, transcripts, logs, or private workspace context.

How to run

The script is in scripts/send.mjs. Requires Node.js 18+ because real sends use native fetch and AbortController.

Basic:

node "<skill-dir>/scripts/send.mjs" --to "you@example.com" --subject "Hello" --body "Hi there"

Without --send, this prints a dry-run payload and does not send. Dry-run output includes the full reviewed body JSON plus body byte length and SHA-256 prefix; redact dry-run logs before sharing externally.

With from address override:

node "<skill-dir>/scripts/send.mjs" --from "Example Sender <onboarding@resend.dev>" --to "you@example.com" --subject "Hello" --body "Hi"

HTML body:

node "<skill-dir>/scripts/send.mjs" --html --to "you@example.com" --subject "Styled" --body "<h1>Hi</h1><p>Hello</p>"

Dry run (no send, just print the payload):

node "<skill-dir>/scripts/send.mjs" --dry-run --to "you@example.com" --subject "Test" --body "..."

Real send (only after explicit approval):

node "<skill-dir>/scripts/send.mjs" --send --to "you@example.com" --subject "Weekly report" --body "Approved report text"

All flags

Recipients in --to, --cc, --bcc, and --reply-to must be bare email addresses. Only --from accepts display-name format such as "Reports <reports@example.com>".

--body-file is intentionally not supported in the public package. Review file contents yourself and pass approved text with --body.

Credentials

Requires process environment values:

• RESEND_API_KEY - starts with re_...
• RESEND_ALLOWED_TO - comma-separated recipient allowlist for real sends
• Real sends require RESEND_ALLOWED_TO; without it the script refuses --send

How to get one:

1. Sign up at https://resend.com and check the current pricing/limits for the account
2. Go to API Keys in the dashboard
3. Click Create API Key, name it, and choose the least-privilege sending permission available for your account
4. Copy the key

Export it in the runtime process environment:

$env:RESEND_API_KEY="<your-resend-key>"
$env:RESEND_ALLOWED_TO="you@example.com,reports@example.com"

Sender identity

By default, emails are sent from onboarding@resend.dev - Resend's default sender. This may support quick testing subject to current Resend account restrictions; use a verified domain/sender for production-style mail.

For a custom domain (later, optional):

1. Add your domain to Resend at https://resend.com/domains
2. Configure DNS records they provide
3. Use a verified sender with --from "Reports <reports@your-verified-domain.example>"

What this skill does

• Reads RESEND_API_KEY from the process environment only
• POSTs a JSON request to https://api.resend.com/emails
• Prints a one-line confirmation with the Resend message ID
• Defaults to dry-run unless --send is present
• Validates basic recipient address shape before sending
• Enforces RESEND_ALLOWED_TO for real sends; fail-closed if it is missing
• Prints body byte length and SHA-256 prefix in dry-run so reviewed content can be matched to the send

What this skill does NOT do

• Does not read or manage email (this is send-only)
• Does not read local files or support --body-file
• Does not write any files
• Does not make network calls other than to api.resend.com
• Does not auto-update
• Does not support attachments in this version

Output

On success:

sent to you@example.com (subject: Hello) - resend-id: c8f43f2a-...

On failure, clear error on stderr with a non-zero exit code.

Troubleshooting

• "RESEND_API_KEY not set" - create one at https://resend.com, check current pricing/limits, and export RESEND_API_KEY in the process environment
• HTTP 401 - API key is invalid or was revoked
• HTTP 403 - API key doesn't have send permission, or the from address can only send to the account owner until a domain is verified (check dashboard). On Windows, a Node.js cleanup assertion may appear after a 403 exit; this is cosmetic and does not indicate a successful send.
• HTTP 422 - the from address isn't verified on your Resend account (use onboarding@resend.dev or verify your own domain)
• HTTP 429 - rate limited; check https://resend.com/pricing or the Resend dashboard for current limits
• Network error or timeout - transient, but a network/timeout/read error after the request was sent does not prove the email was not delivered. Check the Resend dashboard before retrying to avoid duplicate sends.

Sample output

Sanitized representative output for eval/review checks:

$ node scripts/send.mjs --to "you@example.com" --subject "Hello" --body "Hi there"
--- DRY RUN: request would be sent ---
note: add --send to perform a real send after explicit approval.
body: 8 bytes, sha256:8328c36d18b7
WARNING: RESEND_ALLOWED_TO is not configured. Real sends will fail closed until an allowlist is set.
POST https://api.resend.com/emails
Authorization: Bearer [redacted]

{
  "from": "onboarding@resend.dev",
  "to": [
    "you@example.com"
  ],
  "subject": "Hello",
  "text": "Hi there"
}

$ node scripts/send.mjs --send --to "you@example.com" --subject "Hello" --body "Hi there"
error: RESEND_ALLOWED_TO must be set for real sends. Refusing --send without a recipient allowlist.

# PowerShell:
$env:RESEND_ALLOWED_TO="you@example.com"; node scripts/send.mjs --send --to "you@example.com" --subject "Hello" --body "Hi there"
# bash/zsh:
# RESEND_ALLOWED_TO="you@example.com" node scripts/send.mjs --send --to "you@example.com" --subject "Hello" --body "Hi there"
error: RESEND_API_KEY not set in process environment. Create one at https://resend.com, check current pricing/limits, and export RESEND_API_KEY.

Account limits

Resend pricing and free-tier limits can change. Check the current Resend dashboard/pricing page before relying on a specific daily/monthly quota or paid-tier price. New accounts commonly support quick testing from onboarding@resend.dev; use a verified domain/sender for production-style mail.

Changelog

• 1.0.9: Add explicit Node.js 18+ usage prerequisite and offline gate-regression tests for dry-run, allowlist fail-closed, missing-key fail-closed, HTML/reply-to payloads, unsupported body-file, invalid recipients, and help output.
• 1.0.8: Soften public Resend account/default-sender wording to avoid stale pricing/free-tier/domain-setup assumptions.
• 1.0.7: Fix no-allowlist sample output, document bare-recipient requirement and dry-run body visibility, add 30s send timeout, and warn to verify Resend dashboard before retrying ambiguous network/timeout failures.
• 1.0.6: Add frontmatter version metadata, hedge rate-limit wording, document Windows 403 cleanup assertion behavior, and include sanitized dry-run/fail-closed sample outputs for eval review.
• 1.0.5: Public package wording and metadata cleanup; send behavior remains dry-run-first with --send plus recipient allowlist required for real sends.