Giving Claude a role with a system prompt

When using Claude, you can dramatically improve its performance by using the system parameter to give it a role. This technique, known as role prompting, is the most powerful way to use system prompts with Claude.

The right role can turn Claude from a general assistant into your virtual domain expert!

Why use role prompting?

• Enhanced accuracy: In complex scenarios like legal analysis or financial modeling, role prompting can significantly boost Claude's performance.
• Tailored tone: Whether you need a CFO's brevity or a copywriter's flair, role prompting adjusts Claude's communication style.
• Improved focus: By setting the role context, Claude stays more within the bounds of your task's specific requirements.

How to give Claude a role

Use the system parameter in the Messages API to set Claude's role:

import anthropic

client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-sonnet-4-5-20250929",
    max_tokens=2048,
    system="You are a seasoned data scientist at a Fortune 500 company.", # <-- role prompt
    messages=[
        {"role": "user", "content": "Analyze this dataset for anomalies: <dataset>{{DATASET}}</dataset>"}
    ]
)

print(response.content)

Examples

Example 1: Legal contract analysis

Without a role, Claude might miss critical issues:

With a role, Claude catches critical issues that could cost millions:

Example 2: Financial analysis

Without a role, Claude's analysis lacks depth:

With a role, Claude delivers actionable insights: