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Crosslink connects one app you run to one or more devices you own. You write the host, you write (or borrow) the client page, and the SDK owns everything between them: identity, pairing, encryption, capability enforcement, transport selection and reconnection. This section is the developer’s path through that. Read it in order the first time; after that, the API Reference and Configuration are the pages you will keep open.
Three properties fall out of that picture, and most design questions answer themselves once you hold them:
  • The host is the authority. Capabilities are enforced host-side. A client can ask for anything; the host decides. Never gate a sensitive action in client code alone.
  • There is no Crosslink account, and no Crosslink server in the path. A LAN pairing touches nothing you do not run. Signaling and relay are optional, and you can host them yourself.
  • The pairing QR is generated, never assembled. getPairingCode() is the only supported source of a pairing URI. Endpoints come from connectionEndpoints(), which advertises only routes that genuinely exist.

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Build order

1

Decide what the phone is allowed to do

Write the capability list before any code. It is the app’s security model, and retrofitting one is far more work than declaring it up front. See Capabilities and RPC.
2

Stand up a host

createCrosslinkServer, expose, declareEvent, start. Ten minutes. See Your First App.
3

Give the phone a page to load

Serve your client UI from the host’s own listener with lan.httpHandler, so one port serves both the page and the socket. See Serving the client.
4

Pick a network mode

Same-Wi-Fi only, relayed, or reachable from anywhere. See Connection Modes and Remote Access.
5

Harden and ship

Real pairing prompts, device management, revocation, persistence. See Production Checklist.

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Which package do I import?

Full map, including the packages you should not need to import directly, in Package Map. Being explicit about this saves you from designing against the wrong tool:
  • No cloud sync. There is no server holding your data. If two phones must agree while the host is off, Crosslink is not the piece that does it.
  • No user accounts or multi-tenancy. Trust is device-to-host, established by a physical pairing act. There is no notion of “log in as someone else”.
  • No inbound reach it cannot honestly obtain. Behind carrier-grade NAT, the host says so rather than pretending. See Remote Access.