emulate

A service that imitates external platforms such as GitHub, Google, Stripe, and Slack through realistic APIs and authentication flows.

In plain words
What is it for?
Use it for end-to-end tests of integrations, OAuth or OpenID Connect login, billing, email, and other supported service workflows.
Why use it?
It lets tests and demos exercise the application's real integration code without depending on live third-party accounts or services.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/usefulsoftwareco/executor/emulate
Any agent
npx skills add UsefulSoftwareCo/executor --skill emulate
Clone the repo
git clone --depth 1 https://github.com/UsefulSoftwareCo/executor

Made for: Claude Code, Codex.

Per session 89 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,959 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 2 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00089 $0.01959
Opus 5 $0.00044 $0.00979
Sonnet 5 $0.00018 $0.00392
Haiku 4.5 $0.00009 $0.00196

Measured 2d ago against content hash 72b86bc7d435, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

emulate scanned grade B with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Sends data to an external URLmediumData exfiltration

A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.

const created = await fetch("https://resend.emulators.dev/_emulate/instances", { method: "POST" });

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

| `client.state()` / `.logs()` / `.connections()` | Store snapshot, webhook deliveries, copyable SDK/env/curl snippets |
.claude/skills/emulate/SKILL.md · 142 lines

How it starts

The opening of the file, as written. The whole thing — 142 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Emulate: production-fidelity service emulators

@executor-js/emulate (our fork of Vercel Labs' emulate) provides stateful, wire-level emulators for 16 services: github vercel google okta microsoft spotify slack apple aws resend stripe mongoatlas clerk x workos autumn. These are not mocks: real SDKs and real product code run against them unmodified — the cloud e2e target points the actual WorkOS SDK (sealed sessions, JWKS, hosted AuthKit login) and Autumn billing at emulators and exercises the product's real auth code.

This repo only consumes the published npm package. There is no vendor/emulate submodule — everything imports @executor-js/emulate from npm. The emulator source is its own standalone project; to change or deploy an emulator, see "Changing or deploying an emulator" at the bottom.

Two ways to get one

Local, programmatic (what e2e/setup/cloud.boot.ts does):

import { createEmulator } from "@executor-js/emulate";
const github = await createEmulator({ service: "github", port: 4501 });
// github.url, await github.close() — plus the full typed client below

baseUrl sets the advertised origin (redirects, form actions, spec servers) when a proxy fronts the emulator — the bind stays on port.

Attach to a running one (another process, or hosted on Cloudflare with Durable Object state at https://<service>.<instance>.emulators.dev — catalog at GET https://emulators.dev/_emulate/services). Service hosts (https://<service>.emulators.dev) are control plane only, with no shared default instance behind them: create a private instance first and connect to the returned providerBaseUrl.

import { connectEmulator } from "@executor-js/emulate";
const created = await fetch("https://resend.emulators.dev/_emulate/instances", { method: "POST" });
const { providerBaseUrl } = await created.json();
const resend = await connectEmulator({ baseUrl: providerBaseUrl });
// optional: { service: "resend" } verifies the manifest on connect

Read the full file on GitHub · 142 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 142 lines · 89 tokens per session scan B 72b86bc7d435

Subscribe to this mod's changes

emulate is a skill published in the GitHub repository UsefulSoftwareCo/executor (3,466 stars, last pushed yesterday), licensed MIT. It adds 89 tokens to every session and 1,959 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it B with 2 findings (sends data to an external url, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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