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

# Session data

> Read durable per-session values with useSessionData

`useSessionData()` reads structured data associated with the current durable
session. Use it for application context that should influence later renders,
such as a campaign name, locale, audience, or workflow phase.

```tsx theme={null}
import { useSessionData } from "@opencomputer/agent";

export default function Agent() {
  const campaign = useSessionData<string>("campaign_name");
  const audience = useSessionData<string>("audience");

  return [
    "Help plan the campaign.",
    campaign ? `Campaign: ${campaign}.` : undefined,
    audience ? `Audience: ${audience}.` : undefined,
  ]
    .filter(Boolean)
    .join(" ");
}
```

## Read a value

The key is a string. Pass a TypeScript type argument for the expected value:

```tsx theme={null}
const locale = useSessionData<string>("locale");
const approved = useSessionData<boolean>("brief_approved");
const tags = useSessionData<readonly string[]>("tags");
```

The hook returns `undefined` when the key is absent. Handle that case rather
than assuming every session has been initialized.

Values must be JSON-compatible: `null`, booleans, numbers, strings, arrays,
and objects containing those values.

## Configure capabilities from session data

Because session data is available during render, it can control instructions
and resource hooks:

```tsx theme={null}
import { useSessionData, useTool } from "@opencomputer/agent";
import { publishCampaign } from "./tools/publish-campaign";

export default function Agent() {
  const approved = useSessionData<boolean>("brief_approved") ?? false;

  if (approved) {
    useTool(publishCampaign);
  }

  return approved
    ? "The brief is approved. Publishing is available when the user asks."
    : "Draft and revise the brief. Do not publish it yet.";
}
```

## Session data versus input

`useInput().payload` belongs to the current admitted input. Session data is
associated with the durable session and can be read again on later renders.
Use input for the event that just arrived and session data for context that
outlives that event.

## Current write behavior

The current `@opencomputer/agent` API exposes session data as a read-only
snapshot. It does not yet include a hook for setting or updating a value from
agent code. Code should treat the returned value as immutable.

See [Sessions and turns](/agents/sessions) for the durable conversation
lifecycle and the [GTM engineer example](/agents/examples/gtm-engineer) for an
agent that continues user selections and drafting in one session.