# Controlling the Output Format — Prompt Engineering

Source: https://www.geekswithgeeks.com/en/prompt-engineering/c-format

> Ask for lists, tables, JSON or fixed templates.

## Describe the shape, show a sample

State the format explicitly: "a Markdown table with columns Name, Risk, Fix", "exactly 3 bullet points", "JSON with keys title and tags". Showing a **sample output** is even stronger. Specify **length** (words, sentences, bullets), **order**, and what to do when information is missing ("write `unknown`, do not guess"). If another program will read the reply, request a machine-readable format and **validate** it in code (next section) rather than trusting it. Ask for the answer only, without a friendly preamble, when the output feeds a pipeline.

## Prefill the start of the reply

Where the API allows it, begin the assistant message with `{` or `|` to push the model straight into JSON or a table.

**Quiz:** If a program reads the reply, what should you do?

- [ ] Ask for a poem
- [ ] Hope the format is right
- [x] Request a machine-readable format and validate it in code
- [ ] Disable the system prompt

*Answer:* Request a machine-readable format and validate it in code. Models sometimes deviate, so verify before using.