Generate emulate seed configs for stateful API emulation. Wraps Vercel's emulate tool for GitHub, Vercel, Google OAuth, Slack, Apple Auth, Microsoft Entra, AWS (S3/SQS/IAM), Okta, Resend, Stripe, and MongoDB Atlas APIs. Not mocks — full state machines where create-a-PR-and-it-appears-in-the-list, send-an-email-and-retrieve-from-local-inbox. Use when setting up test environments, CI pipelines, integration tests, or offline development.
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Generate emulate seed configs for stateful API emulation. Wraps Vercel's emulate tool for GitHub, Vercel, Google OAuth, Slack, Apple Auth, Microsoft Entra, AWS (S3/SQS/IAM), Okta, Resend, Stripe, and MongoDB Atlas APIs. Not mocks — full state machines where create-a-PR-and-it-appears-in-the-list, send-an-email-and-retrieve-from-local-inbox. Use when setting up test environments, CI pipelines, integration tests, or offline development.
Generate and manage seed configs for emulate (Apache-2.0) — Vercel Labs' stateful API emulation tool. Each category has individual rule files in rules/ loaded on-demand.
Paired agent: This skill pairs with the emulate-engineer subagent (subagent_type: "emulate-engineer"). When a task involves generating a full emulate config from scratch, webhook HMAC setup, CI pipeline integration, or parallel-worker port isolation, spawn the agent rather than handling it inline — it has the full 12-emulator service-port matrix and seed-rules in context.
Not mocks. Emulate provides full state machines with cascading deletes, cursor pagination, webhook delivery, and HMAC signature verification. Create a PR via the API and it appears in GET /repos/:owner/:repo/pulls. Delete a repo and its issues, PRs, and webhooks cascade-delete.
New in 2026-04 (emulate 0.4.x)
Modular @emulators/* packages — each service is its own package (@emulators/github, @emulators/stripe, etc.); top-level emulate re-exports createEmulator and the CLI.
4 new services (12 total): mongoatlas:4007, okta:4008, resend:4009, stripe:4010 with drop-in seed YAML blocks.
Resend local inbox — GET http://localhost:4009/inbox returns captured emails for assertions without hitting a real provider.
Stripe hosted checkout — real session redirect flow + checkout.session.completed/expired webhook delivery, suitable for E2E payment tests.
MongoDB Atlas — Admin API v2 (projects/clusters/DB users) + Data API v1 with full CRUD + aggregate.
Okta OIDC — full discovery, JWKS, authorize/token/userinfo/revoke/introspect plus Users/Groups/Apps CRUD.
@emulators/adapter-next — catch-all Next.js route handler runs emulators on the same origin as the app; fixes OAuth callback URL drift on Vercel preview deploys.
See references/api-coverage.md for full endpoint lists.
Next.js Adapter (0.4+) — @emulators/adapter-next
Runs emulators on the same origin as your Next.js app via a catch-all route handler. Fixes the OAuth callback URL drift problem on Vercel preview deploys — no more http://localhost:4001 redirect mismatches.
See rules/seed-config.md for full schema and best practices.
Programmatic SDK
Service packages live under the @emulators/* scope (e.g., @emulators/github, @emulators/stripe). The programmatic API (createEmulator) is exported from the top-level emulate package.
import { createEmulator } from'emulate'const github = awaitcreateEmulator({ service: 'github', port: 4001 })
// github.url -> 'http://localhost:4001'// State is real — create a PR and it appears in the listconst res = awaitfetch(`${github.url}/repos/org/repo/pulls`, {
method: 'POST',
headers: { Authorization: 'Bearer dev_token' },
body: JSON.stringify({ title: 'Test PR', head: 'feature', base: 'main' })
})
const prs = awaitfetch(`${github.url}/repos/org/repo/pulls`)
// -> includes the PR we just created// Cleanup
github.reset() // Synchronous state wipeawait github.close() // Shut down server
See references/sdk-patterns.md for advanced patterns (multi-service, lifecycle hooks).
Webhook Delivery
Emulate delivers real webhooks with HMAC-SHA256 signatures when state changes:
