Emulate Seed Configs
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: "ork: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 13-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.
- Entra / Apple / Slack expansions (v0.4.0) — PKCE + refresh rotation (Entra), RS256 JWKS (Apple), OAuth v2 consent UI (Slack).
@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.
Auto-Discovery (M125 #4)
scripts/auto-discover.sh scans the project's package.json, matches deps against references/dep-to-emulator-map.json, and either reports the matches or writes emulate.config.yaml. Three modes:
| Mode | Behavior |
|---|
| (default) | Report matched deps + emulator union on stderr; do not write |
--json | Emit machine-readable JSON instead of human report |
--apply | Write emulate.config.yaml (refuses to overwrite without --force) |
$ bash scripts/auto-discover.sh
/ork:emulate-seed --auto — scanning /path/to/package.json
Detected:
@octokit/rest → github · Any GitHub API client
next-auth → google-oauth, apple-auth, microsoft-entra · Default OAuth providers
stripe → stripe
@vercel/blob → aws · @vercel/blob is S3-compatible
Union: apple-auth, aws, github, google-oauth, microsoft-entra, stripe
$ bash scripts/auto-discover.sh --apply
…
✓ Wrote /path/to/emulate.config.yaml with 6 service(s)
Multi-emulator deps default to all reasonable providers; the user prunes the YAML afterwards. Unmapped deps are silently skipped — extending coverage is a docs PR (edit references/dep-to-emulator-map.json), not a code change.
/ork:dev reads the resulting emulate.config.yaml at boot — see src/skills/dev/scripts/boot.sh.
Quick Reference
| Category | Rules | Impact | When to Use |
|---|
| Seed Config | 1 | HIGH | Setting up emulate.config.yaml for test environments |
| Service Selection | 1 | MEDIUM | Choosing GitHub/Vercel/Google for your tests |
| Webhook Setup | 1 | MEDIUM | Testing webhook delivery with HMAC verification |
| Parallel CI | 1 | HIGH | Running tests in parallel without port collisions |
| Auth Tokens | 1 | MEDIUM | Seeding tokens mapped to emulated users |
Total: 5 rules across 5 categories
Quick Start
npm install --save-dev emulate
npx emulate
npx emulate --service github,stripe --seed ./emulate.config.yaml
npx emulate init --service github
Services (0.9.0 — 14 emulators)
New across releases:
- 0.5.0 — added Clerk, MongoDB Atlas, Stripe, Resend, and Okta emulators; portless integration (embedded emulators without dedicated ports); Google OAuth
hd claim support; Stripe Checkout + Resend magic link examples; AWS S3 emulator now matches the official SDK wire format.
- 0.6.0 — expanded Slack (OAuth v2 consent UI, conversations/reactions).
- 0.6.1 — Vercel Blob store.
- 0.7.0 — added Linear (13th provider): stateful orgs/teams/issues/cycles + webhooks.
- 0.8.0 — added Twilio (14th provider): accounts, phone numbers, messages, calls, conversations, messaging services, Verify flows, and simulator endpoints, with a Next.js SMS-verification example.
- 0.9.0 — added a Nuxt emulator adapter (alongside the Next.js adapter); provider count unchanged.
All backwards-compatible.
| Service | Default Port | Coverage |
|---|
| Vercel | :4000 | Projects, deployments, domains, env vars, teams |
| GitHub | :4001 | Repos, PRs, issues, comments, reviews, Actions, webhooks, orgs, teams |
| Google OAuth | :4002 | OAuth 2.0 authorize, token exchange, userinfo |
| Slack | :4003 | Chat, conversations, users, reactions, OAuth v2 with consent UI |
| Apple Auth | :4004 | Sign in with Apple — OIDC discovery, JWKS (RS256), auth flow, token exchange |
| Microsoft Entra | :4005 | OAuth 2.0/OIDC v2.0, authorization code + PKCE, refresh token rotation, v1 token endpoint, Graph /users/{id} |
| AWS | :4006 | S3 buckets, SQS queues, IAM users/roles, STS identity |
| MongoDB Atlas (0.4+) | :4007 | Admin API v2 (projects, clusters, DB users) + Data API v1 (full CRUD + aggregate) |
| Okta (0.4+) | :4008 | OIDC discovery, JWKS, authorize/token/userinfo/revoke/introspect, Users/Groups/Apps CRUD |
| Resend (0.4+) | :4009 | Send + batch (100/req), list/retrieve/cancel, domains, API keys, audiences, contacts, local inbox (GET /inbox) |
| Stripe (0.4+) | :4010 | Customers, payment methods, customer sessions, payment intents, charges, products, prices, hosted checkout session w/ webhook delivery |
| Clerk (0.5+) | (on-demand) | Users, sessions, organizations |
| Linear (0.7+) | (on-demand) |
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.
const { withEmulate } = require('@emulators/adapter-next')
module.exports = withEmulate({ })
import { createEmulateHandler } from '@emulators/adapter-next'
export const { GET, POST } = createEmulateHandler({
services: ['github', 'stripe', 'resend'],
persistence: { },
})
Seed Config Structure
A seed config pre-populates the emulator with tokens, users, repos, and projects so tests start from a known state.
tokens:
dev_token:
login: yonatangross
scopes: [repo, workflow, admin:org]
ci_token:
login: ci-bot
scopes: [repo]
github:
users:
- login: yonatangross
name: Yonatan Gross
- login: ci-bot
name: CI Bot
repos:
- owner: yonatangross
name: my-project
private: false
default_branch: main
topics: [typescript, testing]
vercel:
users:
- username: yonatangross
email: yonaigross@gmail.com
projects:
- name: my-docs
framework: next
okta:
[{ }, { }]
[{ }]
[]
[{ }]
[{ }]
[{ }, { }]
{ , , , { } }
{ , , , { } }
[{ }]
[{ , }]
[{ , }]
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 = await createEmulator({ service: 'github', port: 4001 })
const res = await fetch(`${github.url}/repos/org/repo/pulls`, {
method: 'POST',
headers: { Authorization: 'Bearer dev_token' },
body: JSON.stringify({ title: 'Test PR', head: 'feature', base: 'main' })
})
const prs = await fetch(`${github.url}/repos/org/repo/pulls`)
github.reset()
await github.close()
seed here is a parsed object, not a path. Only the CLI --seed flag takes a filename.
For multi-service setup, lifecycle hooks, and the Vitest/Jest wiring, see
references/upstream.md. For the ork-side corrections to that API, see
references/ork-delta.md.
Webhook Delivery
Emulate delivers real webhooks with HMAC-SHA256 signatures when state changes:
import crypto from 'crypto'
function verifyWebhook(payload: string, signature: string, secret: string): boolean {
const expected = 'sha256=' + crypto
.createHmac('sha256', secret)
.update(payload)
.digest('hex')
return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected))
}
See rules/webhook-setup.md for webhook receiver patterns.
CI Integration
jobs:
test:
steps:
- uses: actions/checkout@v4
- name: Start emulate
run: npx emulate --service github --seed .emulate/ci.yaml &
- name: Wait for emulate
run: sleep 2
- name: Run tests
run: npm test
env:
GITHUB_API_BASE: http://localhost:4001
VERCEL_API_BASE: http://localhost:4000
Parallel Test Execution
Each test worker gets its own port to avoid race conditions:
const workerPort = 4001 + parseInt(process.env.VITEST_WORKER_ID || '0')
See rules/parallel-ci.md for full parallel isolation patterns.
Decision Matrix
| Tool | When to Use | Stateful? | Platforms |
|---|
| emulate (FIRST CHOICE) | GitHub/Vercel/Google/Slack/Apple/Entra/AWS/Okta/Resend/Stripe/MongoDB/Clerk/Linear testing | YES | All 13 services |
| Pact | Contract verification between services | No | Any |
| MSW | In-browser/Node HTTP mocking | No | Any |
| Nock | Node.js HTTP intercept | No | Any |
| WireMock | HTTP stub server | Partial | Any |
Use emulate when:
- Testing code that calls GitHub, Vercel, Google, Slack, Apple, Entra, AWS, Okta, Resend, Stripe, MongoDB Atlas, Clerk, or Linear
- You need state persistence across multiple API calls in a test
- You want webhook delivery with real HMAC signatures (GitHub, Stripe)
- You need cascading side-effects (delete repo -> PRs cascade-delete)
- You need to assert on sent emails without hitting a real provider (Resend local
/inbox)
- You need hosted Stripe checkout sessions with real redirect flow in tests
Use MSW/Nock when:
- Mocking arbitrary HTTP APIs not covered by emulate
- You need in-browser interception (MSW)
- Tests only need single request/response pairs
Upstream coverage (do not restate)
This skill is a wrap plus our delta. emulate ships its own per-service reference docs;
copying them here only produces something that goes stale on the next release. If a
topic below comes up, read the first-party source, not a paraphrase.
| Topic | First-party source |
|---|
Programmatic API (createEmulator, url, reset(), close()), Vitest/Jest wiring, config auto-detection order, token fallback | references/upstream.md (synced from vercel-labs/emulate, skills/emulate/SKILL.md) |
| GitHub endpoint recipes, GitHub App JWT seeding, Octokit and Auth.js base-URL wiring, GitHub OAuth flow | https://github.com/vercel-labs/emulate/blob/main/skills/github/SKILL.md |
Google OIDC discovery, JWKS, authorize/token/userinfo/revoke, PKCE, google-auth-library, Passport, openid-client | https://github.com/vercel-labs/emulate/blob/main/skills/google/SKILL.md |
| Vercel endpoint recipes, cursor pagination, team scoping, integration OAuth flow | https://github.com/vercel-labs/emulate/blob/main/skills/vercel/SKILL.md |
| Every other emulator (Slack, Apple, Entra, AWS, Okta, Resend, Stripe, MongoDB Atlas, Clerk, Linear, Twilio) | https://github.com/vercel-labs/emulate/tree/main/skills |
What stays ours: references/ork-delta.md (the corrections and house conventions that
are not in any vendor doc), references/cli-reference.md, references/api-coverage.md,
references/dep-to-emulator-map.json, scripts/auto-discover.sh, and everything in rules/.
Read references/ork-delta.md before copying any snippet out of a vendor doc. It records
the two API facts vendor prose does not spell out (the exported factory is createEmulator,
and seed in the programmatic options is an object rather than a path) plus the
*_API_BASE env-var convention this repo uses instead of the vendor's *_EMULATOR_URL.
Related Skills
testing-integration — Integration test patterns (emulate as first choice for API tests)testing-e2e — End-to-end test patterns with emulated backendstesting-unit — Unit test patterns (use emulate for API-dependent units)security-patterns — Auth token patterns (emulate token seeding)
CLI Reference
See references/cli-reference.md for all CLI flags and commands.
