json-function

JSON Function Example

Demonstrates the function-style PromptKit pattern: invoke a prompt like a serverless function — structured JSON in, one-shot, JSON out.

What it shows

• WithJSONInput — bind a structured input to the prompt's template variables for a single Send. Top-level fields become {{topic}} / {{audience}}; the whole payload is available as {{input}}.
• WithResponseFormat — request schema-enforced JSON output (works across Claude, OpenAI, and Gemini).
• Empty-message one-shot — passing "" as the message makes the input JSON also fill the user turn, so a single Send is a complete invocation.
• Typed round-trip — unmarshal the JSON response into a Go struct.

The recipe

conv, _ := sdk.Open("./research.pack.json", "plan",
    sdk.WithResponseFormat(&providers.ResponseFormat{
        Type:       providers.ResponseFormatJSONSchema,
        JSONSchema: outputSchema,
        SchemaName: "research_plan",
        Strict:     true,
    }),
)
defer conv.Close()

resp, _ := conv.Send(ctx, "", sdk.WithJSONInput(PlanRequest{
    Topic:    "utility-scale battery storage growth in 2023",
    Audience: "executive",
}))

var plan PlanResponse
json.Unmarshal([]byte(resp.Text()), &plan)

Binding rules

For a JSON object input:

• {{input}} is bound to the whole object (compact JSON).
• Each top-level field is bound to {{field}} — strings pass through verbatim; numbers, booleans, objects, and arrays are bound as their compact JSON.
• Bound variables override open-time WithVariables defaults.
• A real top-level field named input shadows the synthetic whole-object var.

Run it

export OPENAI_API_KEY=your-key   # or ANTHROPIC_API_KEY / GEMINI_API_KEY
go run .

The smoke test (go test ./...) exercises the same path with a mock provider — no API keys required.

Note: prefer WithResponseFormat with a schema over the schemaless WithJSONMode for cross-provider output — WithJSONMode has no effect on Anthropic, which only supports schema-backed structured output.