AI Structured Output / JSON Prompt Builder
Build an AI prompt that reliably returns structured output like JSON or a fixed schema for your app or workflow, free in your browser.
Output spec
Your prompt
Copy-ready prompt
A template built from your inputs — paste it into your AI tool. Runs in your browser; nothing is uploaded.
How to use this calculator
- Describe the task and list your schema fields (name: type — note), one per line.
- Pick the output format and strictness.
- Copy the prompt — the AI returns data in exactly that shape.
How it works
The prompt pins the output to your schema and format, tells the model to use null for unknown fields, keep field names exact, and not wrap the output in prose — which makes the result easy to parse downstream.
It builds the instruction; the structured data itself is produced by your AI tool.
Frequently asked questions
Does this use AI or send my prompt anywhere?
No. It runs entirely in your browser using rule-based checks — your prompt is never uploaded or sent to any AI model. Still, avoid pasting passwords, API keys or private data into any tool.
Why ask for null instead of omitting fields?
Consistent keys make the output easier to parse. Telling the model to use null for unknowns keeps every record the same shape.
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Cite this tool
Zerdly. (2026). AI Structured Output / JSON Prompt Builder. Retrieved from https://www.zerdly.com/tools/ai-structured-output-prompt-builder/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.