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 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:
