vercel-labs-emulate — Claude Code skill: local API emulation

What vercel-labs-emulate does

The skill covers emulate, a set of local servers that take the place of Vercel, GitHub and Google APIs. State lives in memory, and pagination, OAuth, webhooks and cascading deletes behave the way they do in production. Your tests get real responses instead of stubs.

Start it from the CLI: npx emulate brings up every service, npx emulate --service vercel,github picks two, npx emulate --port 3000 sets the base port. Vercel listens on http://localhost:4000, GitHub on http://localhost:4001, Google on http://localhost:4002. You can also set the port through EMULATE_PORT or PORT. A programmatic API exists too: createEmulator({ service: 'github', port: 4001 }) hands back an object with url, reset() and close().

Seed data comes from emulate.config.yaml at the project root, or from an inline seed object. Run npx emulate init to generate the file. Leave oauth_apps out of the config and any client_id is accepted; configure the apps and validation becomes strict. For GitHub Apps, sign the JWT with RS256 and iss set to app_id — the emulator checks the signature.