Resend

Resend

Agent-callable tools for Resend, the email API. Send transactional email to one or more recipients, manage a contact list (create, look up, update, delete contacts and their custom properties), organize contacts into segments and manage segment membership, send a broadcast to an entire segment, read the delivery status of sent email, and check which sending domains are verified. Wraps the public Resend API over a single API-key credential.

Independent, unofficial connector for Resend. Not affiliated with, endorsed by, or sponsored by Resend. "Resend" is a trademark of its owner, used only to identify the service this connector works with.

When to use this

• Send email — a transactional message to specific recipients (sendEmail), or a marketing broadcast to a whole segment (createBroadcast + sendBroadcast).
• Manage contacts — create, retrieve, update, list, and delete contacts, and read a contact's segments; contacts are addressable by id or email address.
• Manage segments — create, list, get, and delete segments (named groupings a contact can belong to), and add or remove contacts.
• Check delivery and diagnose sends — read a sent email's status (getEmail, listEmails), discover custom contact-property keys (listContactProperties), verify sending domains (listDomains), and trigger a configured automation (sendEvent).

Setup

This is an agentskills.io skill.

If the connector has not been installed as a skill yet, install it first with npx skills add zapier/connectors --skill resend (or your harness's own skill-install mechanism), then continue here. Installing the skill copies these files, not dependencies. Before running the CLI, a local MCP server, or zapier-sdk auth commands, run npm install --omit=dev here once. Importing the published package as a dependency in your own project instead? That npm install already resolves everything — see references/use-as-sdk.md.

Want the actual repo source instead — to browse references/, run this connector's tests, or hack on it? See README.md for a scoped git clone.

The connector runs on Node.js 22.18+. Pick the reference that matches how you're running it, and load it before doing anything else:

Scripts

Every script uses the single resend connection. Contact-referencing tools accept a contact id or email address interchangeably.

Disambiguation & refusals

Before writing to a segment or contact looked up by name, resolve the id first and count matches. Segment names and contact names are not unique. When an instruction names a segment (e.g. "add Sarah to the VIP segment") or a person, resolve it via listSegments / listContacts (or getContact by email) and count exact (case-insensitive) matches:

• Exactly one match → act on it. Don't over-ask for confirmation on an unambiguous single match.
• Two or more that tie on the name → stop, list the candidates with a distinguishing field (segment created_at; contact email), and ask which one. Never silently pick the first.

This check still applies even if you already hold a candidate id — e.g. if you just created two segments with the same name earlier in this session. Already knowing one id is not the same as confirming it's the only match: run listSegments / listContacts and count matches before writing, the same as if you'd looked the name up fresh. Don't reuse an id from your own recent tool output as a shortcut past the count-and-ask step.

Prefer addressing contacts by email address when you have it — getContact, updateContact, deleteContact, addContactToSegment, removeContactFromSegment, and listContactSegments all accept an email directly, which sidesteps name collisions entirely.

A successful updateContact custom-property write is not proof the value persisted. Discover valid keys via listContactProperties before writing one you haven't already confirmed. If you write a property under a key you haven't verified, read the contact back (getContact) before reporting it as set — don't rely on the write call's bare success status alone.

Unsupported operations — say so and stop; don't substitute another tool. This connector does not:

• Verify or provision a sending domain — listDomains is read-only (it reports verification status so you can diagnose a failed send). Adding, verifying, or deleting a domain is DNS work done once in the Resend dashboard; there is no tool for it here. If a send fails because a domain isn't verified, report which domain is unverified and point the user to the dashboard — don't claim to have fixed it.
• Author automations — sendEvent triggers an automation a human already configured in the dashboard; it does not create or edit the automation graph. If asked to build an automation flow, say it's unsupported.
• Manage API keys, webhooks, templates, or suppressions, or send batch/base64-attachment email. Attachments are supported only by hosted URL (path), not raw bytes.

Auth

Every shape passes auth as one connection selector, not the secret — a [<resolver>:]<value> string. Every connector accepts zapier:<connection-id> (Zapier-managed auth — routes through Zapier's auth, retries, and governance layer); some also accept one or more direct-token resolvers (naming and count vary per connector) — check this connector's own resolvers rather than assuming. The <resolver>: prefix is optional; a bare value goes to the first resolver that claims it — a UUID-shaped bare value always claims zapier:. Each script declares the connections it needs and the resolvers each accepts. The exact syntax for passing a connection (and how to see this connector's resolver list) differs by shape — see the reference you loaded above.

Checking what's already configured first? Don't dump environment values to do it — env or env | grep <name> prints the value along with the name, leaking a live credential into the transcript if one is set. Check names only (env | cut -d= -f1 | grep -i <name>) or test a known name directly ([ -n "$VAR_NAME" ]).

No connection yet? Pick one — and follow the reference's own flow to obtain it; never just ask the user for a connection id or token as if they already have one memorized:

Output format

Every script returns a { data, meta } envelope:

• data — the script's result (the shape its outputSchema declares; see the reference you loaded above for how to inspect a script's exact schema in your shape).
• meta.outputDataValidation — what validating data did:
  • { skipped: false, droppedPaths: null } — validated, nothing removed.
  • { skipped: false, droppedPaths: [...], instruction } — validated, but those paths were stripped from data: fields the script returned from the API that the outputSchema doesn't declare. If you need them, re-run with output validation skipped.
  • { skipped: true } — validation was bypassed; data is the raw, unchecked script output.

Reading dropped fields / skipOutputDataValidation. To receive the raw, unvalidated result, opt out of output validation (the exact syntax differs by shape — see the reference you loaded above). Input validation is never skipped.

Trimming the result / filterOutputData. To shrink a large result down to the fields you need, pass a jq expression that post-processes data (again, exact syntax per shape). The jq runs against data only, NOT the { data, meta } envelope, so write it rooted at data (run the script's --help — or your shape's equivalent — to see its output schema). The transformed value replaces data, meta is preserved, and the result is NOT re-validated against the output schema.

References

Load the matching reference file before working in that area: