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 the exact to, cc, bcc, from, reply-to, subject, and body. Treat reply-to as response-routing control and review display-name text in from for spoof-like wording before any real send.
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.

For operator workflows, prefer --json so dry-runs and real sends produce a stable machine-readable receipt with mode, sent, recipients, subject, body byte count, full body SHA-256, SHA-256 prefix, allowlist status, and resendId on successful real sends.

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 "..."

If --dry-run and --send are both present, dry-run wins and no email is sent.

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

Flag	Required?	Purpose
--to	yes	Comma-separated recipient addresses
--subject	yes	Message subject
--body	yes	Inline message body
--cc	no	Comma-separated cc
--bcc	no	Comma-separated bcc
--from	no	Override sender, e.g. "Example Sender <onboarding@resend.dev>"
--reply-to	no	Reply-to address
--html	no	Body is HTML instead of plain text
--dry-run	no	Don't send; print the JSON payload
--send	no	Actually send. Without this, the script dry-runs by default
--json	no	Print a stable JSON receipt for dry-run or real send
-h, --help	no	Show help

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
• Supports --json receipt output so automation can compare the reviewed body hash to the send receipt and capture resendId without scraping human text

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-...

With --json, dry-runs and sends emit parseable JSON. Successful real sends include sent: true, bodySha256, bodySha256Prefix, and resendId.

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.

Required checks before publishing/updating

Minimum no-send checks:

node --check skills\resend-send-native-node\scripts\send.mjs
node skills\resend-send-native-node\scripts\send.mjs --help
node skills\resend-send-native-node\scripts\send.mjs --to "test@example.com" --subject "Smoke" --body "Hello" --json
node skills\resend-send-native-node\tests\run-resend-send-tests.mjs

The smoke command above must remain a dry-run: do not include --send. Real sends require separate explicit approval for the exact recipient headers, subject, and body plus an allowlist.

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

• 1.0.15: Document the actual no-send publish/update checks, including the existing tests\run-resend-send-tests.mjs runner, so public update gates do not rely on a nonexistent self-test path. No send behavior change.
• 1.0.14: Public package eval hygiene: generate the Resend API-key-shaped test sentinel at runtime so package scanners do not see a static key-shaped string in source; no send behavior change.
• 1.0.13: Source-polish retest prep: genericized a review fixture subject, documented that --dry-run --send resolves to dry-run, and normalized SKILL.md line endings; no send behavior change.
• 1.0.12: ClawHub publication/version refresh after JSON receipt fix and public-readiness review; no additional runtime behavior change.
• 1.0.11: Add --json structured receipts for dry-run and real send output so operators can capture stable subjects, body hashes, allowlist status, and resendId without scraping human text.
• 1.0.10: Clarify explicit approval must cover all delivery/reply headers (to, cc, bcc, from, reply-to), subject, and body before real sends.
• 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.