Resend

resend-rest-v1restprimary

98% coverage

Offload Valuejudged · weight 15 · Oct 5, 2026

Resend performs a real, irreversible external side effect: actually delivering email over SMTP infrastructure with domain authentication (DKIM/verification), suppression lists, deliverability, and inbound receiving. An agent cannot approximate sending a real email through inference at any token cost. Beyond sending, it provides domain verification, suppression management, webhooks, and delivery metrics capabilities impossible to synthesize locally. Some endpoints are CRUD (templates, contacts, labels), but the core value is the side effect.

• https://resend.com/docs/api-reference/introduction

  Sending POST Send Email POST Send Batch Emails GET Retrieve Sent Email GET List Sent Emails PATCH Update Email POST Cancel Email

• https://resend.com/docs/api-reference/introduction

  Sending POST Send Email POST Send Batch Emails GET Retrieve Sent Email GET List Sent Emails PATCH Update Email POST Cancel Email

• https://resend.com/docs/api-reference/introduction

  Sending POST Send Email POST Send Batch Emails GET Retrieve Sent Email GET List Sent Emails PATCH Update Email POST Cancel Email

Interaction Costmeasured · weight 15 · Sep 21, 2026

Median over 2 successful run(s): 5100.5 tokens, 1 calls. Ratio to the best in "transactional-email" (3 surfaces measured, v0.2 scale). Cold, without documentation: 1/1 succeeded.

Error Recoverabilityprobed · weight 15 · Oct 5, 2026

unknown_endpoint → HTTP 422, clarity 50/100 (field named: no, allowed values: yes, RFC 9457: no) · wrong_type → HTTP 422, clarity 75/100 (field named: yes, allowed values: yes, RFC 9457: no) · hallucinated_enum → HTTP 200, clarity 30/100 (field named: no, allowed values: no, RFC 9457: no) · unknown_field → HTTP 200, clarity 30/100 (field named: no, allowed values: no, RFC 9457: no) · missing_required_param → HTTP 422, clarity 25/100 (field named: no, allowed values: no, RFC 9457: no) · idempotency_replay → HTTP 200, clarity 25/100 (field named: no, allowed values: no, RFC 9457: no)

• https://api.resend.com/domains

  HTTP 401: {"statusCode":401,"message":"Missing API Key","name":"missing_api_key"}

• https://api.resend.com/domains/nonexistent_resource_xyz

  HTTP 422: {"statusCode":422,"message":"The `id` must be a valid UUID","name":"validation_error"}

• https://api.resend.com/domains?limit=not_a_number

  HTTP 422: {"statusCode":422,"message":"The `limit` field must be a `number`.","name":"validation_error"}

• https://api.resend.com/domains?status=nonexistent_status

  HTTP 200: {"object":"list","has_more":false,"data":[{"id":"ff5340bf-5fde-4779-9e22-ee85c2c23e8f","name":"founderquest.app","status":"verified","created_at":"2026-09-28 04:33:52.822612+00","region":"eu-west-1","

Doc Legibilitymeasured · weight 12 · Oct 5, 2026

text/markup ratio 1.5% (weight 30) · rendering without JavaScript undetermined (excluded from the calculation) (weight 25) · machine-readable spec: https://resend.com/openapi.json (weight 25) · llms.txt: https://resend.com/llms.txt (weight 10) · 1 runnable example(s) (weight 10). Weighted average over 75 points of available sub-criteria.

• https://resend.com/docs/api-reference/introduction
• https://resend.com/openapi.json
• https://resend.com/llms.txt

Auth Frictionmeasured · weight 10 · Oct 5, 2026

Authorization: Bearer <key>, verified by a successful call. One header, no ceremony.

• https://api.resend.com/domains

  HTTP 401: {"statusCode":401,"message":"Missing API Key","name":"missing_api_key"}

• https://api.resend.com/domains/nonexistent_resource_xyz

  HTTP 422: {"statusCode":422,"message":"The `id` must be a valid UUID","name":"validation_error"}

• https://api.resend.com/domains?limit=not_a_number

  HTTP 422: {"statusCode":422,"message":"The `limit` field must be a `number`.","name":"validation_error"}

• https://api.resend.com/domains?status=nonexistent_status

  HTTP 200: {"object":"list","has_more":false,"data":[{"id":"ff5340bf-5fde-4779-9e22-ee85c2c23e8f","name":"founderquest.app","status":"verified","created_at":"2026-09-28 04:33:52.822612+00","region":"eu-west-1","

Safety & Reversibilityprobed · weight 10 · Oct 5, 2026

Two identical POSTs with the same Idempotency-Key header return the same resource (01a10bfd-3437-7548-9431-cb260319e0a5). An agent can retry without risking a duplicate. (weight 35) · No isolated test environment: any experiment hits production. (weight 25). Weighted average over 60 points of measured sub-criteria.

• https://api.resend.com/domains

  HTTP 401: {"statusCode":401,"message":"Missing API Key","name":"missing_api_key"}

• https://api.resend.com/domains/nonexistent_resource_xyz

  HTTP 422: {"statusCode":422,"message":"The `id` must be a valid UUID","name":"validation_error"}

• https://api.resend.com/domains?limit=not_a_number

  HTTP 422: {"statusCode":422,"message":"The `limit` field must be a `number`.","name":"validation_error"}

• https://api.resend.com/domains?status=nonexistent_status

  HTTP 200: {"object":"list","has_more":false,"data":[{"id":"ff5340bf-5fde-4779-9e22-ee85c2c23e8f","name":"founderquest.app","status":"verified","created_at":"2026-09-28 04:33:52.822612+00","region":"eu-west-1","

Payload Efficiencyprobed · weight 8 · Oct 5, 2026

No discoverable field selection (tested fields, select, _fields, expand, properties): the agent swallows the whole resource. (weight 35) · 262 bytes per returned object (3 object(s) in the control response). (weight 25) · Cursor pagination detected ("has_more"). (weight 20) · One list envelope, standard. (weight 10) · ETag present: an agent can avoid re-downloading. (weight 10). Weighted average over 100 points of measured sub-criteria.

• https://api.resend.com/domains

  HTTP 401: {"statusCode":401,"message":"Missing API Key","name":"missing_api_key"}

• https://api.resend.com/domains/nonexistent_resource_xyz

  HTTP 422: {"statusCode":422,"message":"The `id` must be a valid UUID","name":"validation_error"}

• https://api.resend.com/domains?limit=not_a_number

  HTTP 422: {"statusCode":422,"message":"The `limit` field must be a `number`.","name":"validation_error"}

• https://api.resend.com/domains?status=nonexistent_status

  HTTP 200: {"object":"list","has_more":false,"data":[{"id":"ff5340bf-5fde-4779-9e22-ee85c2c23e8f","name":"founderquest.app","status":"verified","created_at":"2026-09-28 04:33:52.822612+00","region":"eu-west-1","

Task Atomicitymeasured · weight 6 · Sep 21, 2026

Median over 2 successful run(s): 5100.5 tokens, 1 calls. Ratio to the best in "transactional-email" (3 surfaces measured, v0.2 scale). Cold, without documentation: 1/1 succeeded.

Prior Knowledge Coveragemeasured · weight 5 · Sep 21, 2026

Median over 2 successful run(s): 5100.5 tokens, 1 calls. Ratio to the best in "transactional-email" (3 surfaces measured, v0.2 scale). Cold, without documentation: 1/1 succeeded.

Async Compatibilityprobed · weight 2 · Oct 5, 2026

POST /emails returns an identifier, and GET /emails/{id} reads it back (HTTP 200): the result can be retrieved by polling, with no server to host. Long-polling / SSE not probed, excluded from the weighting.

• https://api.resend.com/domains

  HTTP 401: {"statusCode":401,"message":"Missing API Key","name":"missing_api_key"}

• https://api.resend.com/domains/nonexistent_resource_xyz

  HTTP 422: {"statusCode":422,"message":"The `id` must be a valid UUID","name":"validation_error"}

• https://api.resend.com/domains?limit=not_a_number

  HTTP 422: {"statusCode":422,"message":"The `limit` field must be a `number`.","name":"validation_error"}

• https://api.resend.com/domains?status=nonexistent_status

  HTTP 200: {"object":"list","has_more":false,"data":[{"id":"ff5340bf-5fde-4779-9e22-ee85c2c23e8f","name":"founderquest.app","status":"verified","created_at":"2026-09-28 04:33:52.822612+00","region":"eu-west-1","

Tool-Native (MCP)binary · weight 2

Does the vendor publish an official, maintained MCP server?