Resendresend.com
Resend's API program has strong foundations in contract design, schema quality, and crawlability — partners and agents can find and read the spec reliably. The critical gaps are in agent understanding and runnable usability: AI agents lack the semantic operation context and a dedicated instructions file they need to act on the API autonomously, and there are no executable collections with test scripts to validate real workflows.
API DesignA clean, typed, well-governed API contract agents can reason about3 pass2 warn0 fail92A+
| Signal | Points | Findings | Rationale | |
|---|---|---|---|---|
| pass | Auth declared & discoverablevia spec | 25/25 | Authentication required (global or on every operation). Investigated: spec 100%, docs 100%. | Agents can only authenticate when auth is declared, scoped, and discoverable. |
| warn | Schema coverage & depthvia sdk | 22.4/25 | 6 of 249 public signatures use loose types (anyTypeRatio=0.024). Investigated: sdk 90%, spec 67%. | Typed, complete request/response schemas are what make agent function-calling possible. |
| warn | Machine-readable, versioned contractvia spec | 18.8/25 | info.version="1.5.0" set but no versioning scheme (URL / header / media type) detected. Investigated: spec 75%, docs 50%. | A current OpenAPI version with a declared versioning scheme lets agents reason about the contract. |
| pass | Security & governance hygienevia spec | 15/15 | No credential-shaped strings detected in spec. Investigated: spec 100%, wellknown 50%. | No leaked secrets, no critical lint violations, no OWASP API Top-10 spec smells, and a published vulnerability-disclosure channel. |
| pass | Example coveragevia sdk | 10/10 | README is present and includes a runnable quickstart. Investigated: sdk 100%, spec 0%, docs 0%. | Examples carry shape semantics schemas under-specify — for humans and agents alike. |
Developer ExperienceThe context both developers and agents need to integrate fast — onboarding, code samples, complete descriptions and worked examples3 pass1 warn1 fail75B
| Signal | Points | Findings | Rationale | |
|---|---|---|---|---|
| pass | Self-service developer portalvia docs | 29/29 | Self-service signup at https://resend.com/signup; free tier / sandbox documented. Investigated: docs 100%. | Self-serve key/account creation is the fast first call for partners, with no sales gate. |
| pass | Description completenessvia spec | 15/15 | 92% of operations + parameters have substantive descriptions. Investigated: spec 100%, sdk 94%. | Complete descriptions are the context humans and agents need to use endpoints. |
| pass | Changelog publishedvia spec | 13/13 | changelog documented in the docs site at https://resend.com/changelog. Investigated: spec 100%, docs 100%, sdk 100%. | A published changelog lets partners track changes without surprise. |
| warn | Quickstart presentvia docs | 12.5/25 | Quickstart page reachable (1 variants scanned starting at https://resend.com/signup) but no runnable code sample detected in HTML or .md variant. Investigated: docs 50%. | A quickstart is the fastest path from landing page to first successful call. |
| fail | Code samples in docsvia docs | 0/18 | No detectable code samples across 20 sampled docs pages. Investigated: docs 0%. | Multi-language samples shorten time-to-first-call. |
Agent DiscoveryPartners and their agents can find your APIs — llms.txt, registries, crawlable and reachable docs3 pass1 warn0 fail97A+
| Signal | Points | Findings | Rationale | |
|---|---|---|---|---|
| pass | llms.txt present, valid & comprehensivevia docs | 30/30 | llms.txt found at 2 locations; using https://resend.com/docs/llms.txt as canonical. Investigated: docs 100%, sdk 0%. | A valid, comprehensive llms.txt is the machine-readable entry point for agents. |
| pass | Docs reachable, not hard auth-gatedvia docs | 30/30 | All 1 pages are publicly accessible. Investigated: docs 100%. | Agents can only index and fetch docs they can reach — past auth gates and over correct HTTP semantics. |
| pass | Registry & SDK presencevia docs | 28/28 | Indexed on Context7 (websites/resend, 5371 snippets). Investigated: docs 100%, cli 100%, sdk 92%, mcp 0%, wellknown 0%. | Listing in MCP registries and publishing SDKs puts the API where agents and their tooling look. |
| warn | Crawlable / AEOvia wellknown | 9/12 | Sitemap present (11 entries) but carries no lastmod values. Investigated: wellknown 75%. | Bots allowed plus a fresh sitemap make docs findable by agent crawlers. |
Agent UnderstandingAgents can correctly interpret your APIs — machine-readable errors, consistent descriptions, structured data, parseable docs3 pass1 warn2 fail68C
| Signal | Points | Findings | Rationale | |
|---|---|---|---|---|
| pass | Machine-readable errors (RFC 9457)via spec | 28/28 | error codes documented in the docs site at https://resend.com/docs/api-reference/errors. Investigated: spec 100%, docs 100%, sdk 100%. | RFC 9457 problem details and a documented error-code inventory let agents parse failures without burning tokens. |
| pass | Agent-navigable, token-efficient docsvia docs | 22/22 | All 1 pages contain server-rendered content. Investigated: docs 100%. | Server-rendered, clean, small-footprint docs are what an agent can cheaply fetch and parse correctly. |
| pass | Docs structured datavia docs | 8/8 | JSON-LD Article markup on 20/20 assessed pages (100%) with dateModified present. Investigated: docs 100%. | Structured data (JSON-LD/schema.org) on docs pages gives agents an unambiguous parse target and is what answer engines cite. Detected on the JS-rendered head (Firecrawl) for a bounded page budget, so JS-injected JSON-LD is now caught; pages we can't render are excluded rather than failed. |
| warn | Description consistency across surfaces | 1.5/7 | Mean pairwise description similarity across 2 surfaces (docs, sdk) is 8% (threshold 35% for full credit). | Every surface tells the same story about what the product is. |
| fail | Operation purpose clarityvia spec | 0/25 | 0% of operations are agent-inferable. Investigated: spec 0%. | Agents select the right endpoint from its summary + operationId; clear, named operations make tool-selection reliable — the strongest driver of correct tool choice. |
| fail | Agent instructions file (AGENTS.md)via wellknown | 0/10 | No AGENTS.md at the site root or /.well-known/. Investigated: wellknown 0%. | An AGENTS.md gives coding agents explicit setup, auth, and usage instructions to interpret and operate the API — beyond llms.txt's link index. |
Agent UsabilityAgents have the context to use your APIs reliably, not just find them4 pass0 warn1 fail92A+
| Signal | Points | Findings | Rationale | |
|---|---|---|---|---|
| pass | Idempotency documentedvia spec | 27/27 | idempotency documented in the docs site at https://resend.com/docs/dashboard/emails/idempotency-keys. Investigated: spec 100%, docs 100%, sdk 100%. | Documented idempotency lets agents retry safely. |
| pass | Rate-limit signalingvia spec | 22/22 | rate-limit behavior documented in the docs site at https://resend.com/docs/api-reference/rate-limit. Investigated: spec 100%, docs 100%. | Machine-readable rate-limit headers let agents throttle adaptively. |
| pass | Pagination documented & consistentvia spec | 22/22 | Pagination params detected on 23 list endpoint(s). Investigated: spec 100%, docs 100%, sdk 0%. | Consistent, documented pagination lets agents traverse collections. |
| pass | Sandbox separationvia sdk | 20/20 | Sandbox environments are exposed (sandbox). Investigated: sdk 100%, spec 0%, docs 0%. | An isolated environment lets agents exercise destructive operations safely. |
| fail | Runnable collection with test scriptsvia platform | 0/9 | No public Postman workspace discovered for the org. Investigated: platform 0%. | A public, maintained collection with assertions is runnable truth agents validate against. |
Resources Discovered
The public resources we found for Resend — the evidence behind the score. All discovered from public sources; nothing here requires access to your systems.
| Agent hints | Context7 (5,371) |
|---|---|
| APIs analyzed | 1 — Resend |