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

Defined in: [src/types/messages.ts:753](https://github.com/strands-agents/harness-sdk/blob/c3b403c7c41f9fe7b7e704bb8f8d2e6698d3b97e/strands-ts/src/types/messages.ts#L753)

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.