```ts
type SystemPromptData = string | SystemContentBlockData[];
```

Defined in: [src/types/messages.ts:751](https://github.com/strands-agents/harness-sdk/blob/576da59fdc411b55036a7cf66d4e1659a67d4d0d/strands-ts/src/types/messages.ts#L751)

Data representation of a system prompt. Can be a simple string or an array of system content block data for advanced caching.

This is the data interface counterpart to SystemPrompt, following the “Data” pattern.