> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tinycloud.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Build on Node

> Decide between private-key sign-in and session-only mode before your first backend write.

Choose this path when you are building a backend service, job, or CLI with the
Node SDK.

## Choose the authentication mode

* Use private-key mode when the process owns a space and must sign in or create
  delegations.
* Use session-only mode when the process only consumes access delegated by
  another principal.

## Get to a first write

Go directly to the [Node SDK quickstart](/quickstart/node-sdk). It shows the
wallet-backed path from installing the SDK to signing in and writing a KV
record, then introduces session-only mode as the alternative.

## After the first write

* Use [Node sign-in](/guides/authentication/node) when you need to compare the
  two authentication modes in detail.
* Read [DID formats](/concepts/did-formats) before choosing a persistent owner
  DID or ephemeral session DID as a delegation target.
* Read [Spaces](/guides/spaces) when the service must provision additional data
  containers.
* Continue with [Delegations](/guides/delegations) when the service acts on
  behalf of another principal.
* Use the [Node SDK reference](/reference/sdk/node) for the current constructor
  options and primary methods.

## Source note

Use `tc.did` after `signIn()` when you need the owner DID for delegations. In
session-only mode, the delegation must target the instance's session DID.