About StrictJSON
Large language models are good at writing text and unreliable at writing structured data. Ask one for JSON and you often get markdown fences, missing fields, invented values, or a shape that changes from one call to the next. StrictJSON exists to close that gap: it produces a strict system prompt and matching validation code, so the model’s output can be checked by your program instead of trusted on faith.
What it does
You describe the data you need — an order, a book record, a contact form — and pick a format. StrictJSON returns three things that belong together: a system prompt that tells the model to output only a valid JSON object matching the schema, the JSON Schema itself (Draft-07), and the validation code for your stack: Zod for TypeScript, Pydantic v2 for Python, or plain JSON Schema. The prompt, the schema, and the code are generated as one unit, so they agree with each other instead of drifting apart.
Who it is for
StrictJSON is for developers who wire a language model into real code: TypeScript and Python developers building features that depend on structured output, and anyone who has had a pipeline break because the model returned something almost right. No account is needed and nothing is installed — you describe what you need, copy the result, and paste it into your project.
How it works
Behind the tool, two tamed models work in a chain on the server: the first generates the system prompt, the JSON Schema, and the validation code; the result is then checked automatically. If the output is invalid JSON, or if a deterministic quality check finds a known gap — an email field validated by format alone, an optional string that would accept an empty value, an identifier pattern that forbids hyphens — one repair attempt is made with the next model in the chain. A repaired result is flagged so you know to double-check it; if no model produces a usable result, the tool returns a clean error instead of broken code. The chain runs through Gemini, then Groq, then OpenRouter, and you never need an API key of your own: the first 10 generations per day are free. If you need more, you can use your own OpenRouter key, which stays in your browser and is never sent to the server.
Start here
- The tool — describe your data and generate a prompt, a schema, and validation code.
- The library — 12 ready-made entries, from ISBN extraction to order details, each with its prompt, schema, and code ready to copy.