Emulate — emulate third-party APIs

**Status:** Assimilation research note (no code change beyond the atlas record).

**Date:** 2026-06-23.

**Tagline (requester):** "Emulate third-party APIs."

**Method:** vendor homepage <https://emulate.dev> + npm/GitHub corroboration. Behavioral claims are vendor-stated and not independently exercised.

**Provenance (verified 2026-06-23):** open source, **Apache-2.0**, by **Vercel Labs** — github.com/vercel-labs/emulate, npm emulate (v0.7.0) + @emulators/* adapters. npm tagline: "Local drop-in replacement services for CI and no-network sandboxes."

**Atlas record:** tool:emulate-dev — packages/atlas/graph/domain/tools/emulate-dev.yaml (evidence evidence:emulate-dev-homepage-2026-06, evidence:emulate-dev-npm-2026-06).

---

0. Bottom line

A CLI that runs **offline, stateful local replicas of ~11 popular third-party services** (Stripe, GitHub, Google, AWS, Slack, …) speaking their **real protocols** — no network, API keys, or real accounts. Built for local dev and CI: deterministic, zero-config, state persists across requests.

1. What it does

Stand-in services you can develop and test against without touching production APIs: create repos and push commits, charge cards, exchange OAuth tokens — and the emulated state sticks across requests within a run.

2. How it works

• Emulates **authentic protocols**: OAuth with **RS256** tokens, **AWS XML** responses, etc. — not just static stubs.
• **Stateful**: operations mutate persistent in-emulator state.
• **Offline & CI-ready**: deterministic results across environments, no secrets.
• Services bind to HTTPS localhost endpoints (e.g. https://stripe.emulate.localhost); integrates with **Portless** for the named-host routing.
• SDKs are pointed at the local host/port (e.g. localhost:4010) via host/port/protocol config.

3. Install & usage

npx emulate --portless                 # run with Portless routing
npx emulate --service github,stripe    # select services

Programmatic + framework integration:

import { createEmulator } from "emulate"
// Next.js adapter:
// npm install @emulators/adapter-next @emulators/github

4. Relevance to babysitter / agent workflows

• **Deterministic, offline integration tests** are exactly what the live-stack / E2E lanes need to avoid flaky external dependencies and secret management — cf. the published live-stack work where real third-party installs/auth were a recurring blocker.
• An orchestrated agent could target emulated Stripe/GitHub/AWS to exercise tool-service-integration flows hermetically.
• Recorded as catalog awareness (used_for: skill-area:tool-service-integration-agents); not wired into babysitter test infra.

5. Comparison (atlas edges)

alternative_to: tool:wiremock (generic HTTP stub server vs. stateful, protocol-accurate named-service emulation), tool:pact (consumer-driven contract testing vs. runnable stateful service replicas).

6. Caveats / open questions

• License/OSS/repo **verified** (Apache-2.0, Vercel Labs) via npm + GitHub; the Next.js adapter (@emulators/adapter-next) explicitly targets the Vercel preview-deploy OAuth-callback problem. Early version (0.7.x).
• The exact 11 services, per-service fidelity, and the localhost:4010 vs. *.emulate.localhost addressing modes are vendor claims, not independently exercised here.