One of the most underused skills in prompt engineering is explicitly specifying output format. Most beginners let the AI decide how to structure its response. Professionals don't — they specify it in the prompt.
This single habit will save you hours of reformatting AI outputs.
Why Format Matters
AI models default to verbose, essay-style responses unless told otherwise. The model has no idea whether you want:
- A bullet list or a paragraph
- One sentence or five pages
- JSON or plain prose
- Headers and sections or continuous text
- A table or a numbered list
If you don't specify, the model guesses. And it often guesses wrong for your use case.
The Four Format Levers
1. Structure
Tell the AI exactly how to organize its output.
Bad: "Explain the pros and cons of remote work."
Good: "Explain the pros and cons of remote work.
Format:
Pros: [3 bullet points]
Cons: [3 bullet points]
Verdict: [1 sentence]"
2. Length
Specify word count, sentence count, or character limits.
"Summarize this article in exactly 3 sentences."
"Write a tweet about this topic — max 280 characters."
"Give me a 500-word overview, no more."
"Answer in one sentence only."
3. Style
Control tone, vocabulary level, and voice.
"Use simple language — no jargon. Write for someone with no technical background."
"Write in a confident, direct tone. No hedging or excessive caveats."
"Match the tone of the sample text below."
4. Exclusions
Tell the AI what NOT to include.
"Do not include an introduction or conclusion — just the main points."
"No bullet points. Use short paragraphs only."
"Don't add any commentary or preamble. Output only the requested content."
Common Format Templates
Bullet list
List [N] [items] as bullet points. Each bullet should be one sentence.
Numbered steps
Give me step-by-step instructions for [task].
Format: numbered list, each step on its own line, max 2 sentences per step.
Table
Compare [A] and [B] across the following dimensions: [dim1], [dim2], [dim3].
Format as a markdown table with those dimensions as rows.
JSON output
Extract the following from the text and return as JSON:
{
"name": string,
"email": string,
"company": string,
"request": string
}
Text: [text]
Headers and sections
Write a report covering: [topic].
Structure it with these H2 sections:
- Overview
- Key Findings
- Risks
- Recommendations
Keep each section under 150 words.
Closing the Loop: Say "Only Output X"
The most powerful format instruction is also the simplest: tell the model to output only what you asked for.
Output only the JSON object. No explanation, no code blocks, no preamble.
Return only the revised paragraph. Do not explain what you changed.
List only the 5 items. Nothing else.
This eliminates the AI's tendency to wrap your output in commentary, explanations, or "Sure! Here's..." preamble that you'll have to strip out.
Key Takeaway
Never let the AI decide how to format your output. Specify structure, length, tone, and exclusions explicitly. Add "output only [X]" to cut the filler. This single habit makes AI outputs immediately usable instead of requiring cleanup.
Next: Learn How LLMs Actually Work — understanding the mechanism behind AI helps you prompt it better.