Claude API

What are the formatting best practices for Claude system prompts?

Last verified: July 2026 · 2 min read
QUICK ANSWER

Structure your system prompts using XML tags (e.g., <instructions>, <context>, <rules>) to separate guidelines and instruction blocks, which matches Claude's pre-training.

System Prompt Template

<system_instructions>
  <persona>
    You are an API error code reference system.
  </persona>
  <rules>
    1. Output only JSON formatted content.
    2. Do not explain your choices.
  </rules>
</system_instructions>
Verified against: Anthropic Prompt Engineering Guidelines

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