Let Agents In

Agent readiness · Transactional email APIs

resend.com

14 of 16 measurable points under formula 9.2, measured on 2026-08-12. 15 checks exist; each is one HTTP request with a published rule, so every sentence below can be rerun and argued with.

A · Discovery

  • PASS
    Answers an agent user-agentAnswered 200 to LetAgentsIn/1.0 (+https://letagentsin.com/methodology)
  • PASS
    llms.txt publishedllms.txt and llms-full.txt present at https://resend.com/llms.txt and https://resend.com/llms-full.txt, and the 12 links we sampled across both files all answer
  • PASS
    Docs readable without JavaScript8,672 characters of text without JS, on https://resend.com/docs/api-reference/api-keys/list-api-keys rather than on https://resend.com/docs/introduction
  • PASS
    On-demand agents not blockedNo on-demand agent is blocked
  • N/A
    Paths robots.txt points at answerrobots.txt names no concrete path, only patterns or nothing, so there is no claim to check
  • PASS
    No punishing crawl delayNo Crawl-delay applies to the agents we check

B · Agent entry

  • PART
    Agent entry pointFound https://resend.com/agent.md, but it states a policy rather than a procedure: nothing in it names a credential, an endpoint or a way to get an account.
  • PASS
    OAuth dynamic client registrationregistration_endpoint published, but none of the 2 advertised grants (authorization_code, refresh_token) finishes without a person at a browser
  • PASS
    MCP surfaceLive MCP endpoint at https://mcp.resend.com/mcp, answered 401 with an auth challenge

C · Registration

  • PASS
    No CAPTCHA in the signup HTMLNo CAPTCHA vendor in the server HTML. A widget mounted later by JavaScript would not show here. The page does carry kasada, a bot defence that decides in the background rather than a challenge anyone solves. We did not submit the form, so whether it lets an unattended request through is not something we measured.
  • PASS
    Signup reachable without a browserForm renders in server HTML at https://resend.com/signup

D · Provisioning

  • PART
    Programmatic key provisioning1 of 7 provisioning phrases across the 6 documents we read: "create an api key (or api token, access token, personal access token, service account, auth token, secret key), next to something programmatic"
  • PASS
    Free tier or no-card trial stated in textFree tier or no-card signals at https://resend.com/pricing: "free trial", "$0"

E · Integration

  • PASS
    Typed SDK on the registryresend@6.19.0 ships types, matched from the registry by who publishes it rather than by a link on your site
  • PASS
    Machine-readable API descriptionOpenAPI at https://resend.com/openapi.json

Tell me when this changes

The failures here are the kind nobody notices. An edge rule that starts refusing agents changes nothing a person sees in a browser, so the first sign is usually an integration that quietly stopped working. We rescan weekly and write only when a verdict moves.

This page is the newest scan we hold for resend.com and changes when we rescan. It is not a judgement of the product: we measure whether an unattended run can get through, not whether the thing is any good. The whole corpus is published as JSON and CSV.

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