Prompt Templates

Prompt templates are reusable prompts with placeholders for the parts that change, like the user question or a document. Templates keep prompts consistent across your app and make them easy to test and improve.

A Simple Template in Python

TEMPLATE = """You are a friendly product copywriter.
Write a {length}-word description of the product below for {audience}.
Highlight: {highlights}.

<product>
{product}
</product>"""

prompt = TEMPLATE.format(
    length=50,
    audience="busy parents",
    highlights="dishwasher safe, BPA free",
    product="Kids' lunch box with 4 compartments",
)
print(prompt)

You are a friendly product copywriter.
Write a 50-word description of the product below for busy parents.
Highlight: dishwasher safe, BPA free.

<product>
Kids' lunch box with 4 compartments
</product>

A Template in JavaScript

const reviewPrompt = ({ language, code }) => `Review this ${language} code.
List bugs first, then style issues. Max 5 bullets.

<code>
${code}
</code>`;

console.log(reviewPrompt({ language: 'Python', code: 'print(1/0)' }));

Review this Python code.
List bugs first, then style issues. Max 5 bullets.

<code>
print(1/0)
</code>

Good Template Practices

• Keep templates in their own files, not scattered across the codebase.
• Version them (v1, v2) and record which version produced each output.
• Wrap inserted user content in delimiters so it is clearly data.
• Trim or limit variable content to stay inside the context window.
• Test every template change against a fixed set of examples (see Evaluation).

Templates for Chat APIs

For chat models, a template is usually a list of messages: a fixed system message, optional few-shot turns, and a user message built from variables.

messages = [
    {"role": "system", "content": SYSTEM_PROMPT_V3},
    {"role": "user", "content": f"<question>{question}</question>"},
]

(sent to any chat-completion style API)

Frequently asked questions

Do I need a library for prompt templates?

No. String formatting is enough for most apps. Frameworks add features like versioning and tracing if you need them.

How should I store prompts?

In version control alongside your code, or in a prompt management tool with versions and change history.

Is it safe to insert user input into a template?

It is necessary, but treat it as untrusted: use delimiters and defend against prompt injection.