Claude 4.x Prompt Engineering

Core Principles

1. Be Explicit — Claude 4.x follows instructions literally. Request "above and beyond" behavior explicitly.

2. Context Over Commands — Explain WHY, not just WHAT. Claude generalizes from explanations.

3. Positive Framing — Say what TO DO, not what NOT to do.

4. XML Structure — Use XML tags for complex instructions. Claude responds well to structured prompts.

5. Match Style — Your prompt's formatting influences Claude's output formatting.

Workflow

Step 1: Identify Prompt Type

Step 2: Apply Core Transformations

Transform vague → explicit:

Before: "Create a dashboard"
After:  "Create a dashboard with filtering, sorting, and export. Include interactive charts and responsive design."

Transform commands → context:

Before: "NEVER use ellipses"
After:  "Output will be read by TTS, so avoid ellipses which TTS cannot pronounce."

Transform negative → positive:

Before: "Don't use bullet points"
After:  "Write in flowing prose paragraphs"

Step 3: Structure with XML

For complex prompts, wrap sections in XML tags:

<role>
Define who Claude is and their expertise
</role>

<guidelines>
Behavioral guidelines and approach
</guidelines>

<constraints>
Hard limits and requirements
</constraints>

<output_format>
Expected structure of responses
</output_format>

Step 4: Add Relevant Patterns

Select patterns from patterns.md based on needs:

• •Action control: <default_to_action> or <do_not_act_before_instructions>
• •Tool usage: <use_parallel_tool_calls> or <sequential_execution>
• •Code quality: <minimal_implementation>, <investigate_before_answering>
• •Output: <avoid_excessive_markdown_and_bullet_points>

Step 5: Validate

Check the prompt against:

• • No vague modifiers ("be detailed", "be concise" without specifics)
• • No contradictions ("thorough but brief")
• • No negative-only instructions (all "don't" have a "do instead")
• • No assumed context (all needed info is provided or referenced)
• • No over-emphasis for Opus 4.5 (avoid "CRITICAL", "MUST", "ALWAYS" unless truly necessary)

Quick Patterns

Make Claude Act (Not Just Suggest)

<default_to_action>
Implement changes rather than suggesting them. If intent is unclear, infer the most useful action and proceed.
</default_to_action>

Prevent Over-Engineering

<minimal_implementation>
Only make changes directly requested. Keep solutions simple. Don't add features or refactor beyond the ask.
</minimal_implementation>

Force Investigation First

<investigate_before_answering>
ALWAYS read relevant files before proposing edits. Do not speculate about code you haven't inspected.
</investigate_before_answering>

Control Output Format

<output_style>
Write in flowing prose paragraphs. Reserve markdown for code blocks and simple headings only.
</output_style>

Reference Files

• •patterns.md — Complete XML patterns library with copy-paste templates
• •examples.md — Before/after transformations and full system prompt examples
• •agentic.md — Multi-context window tasks, state management, subagent orchestration

Model-Specific Notes

Opus 4.5

• •Very responsive to system prompts — dial back aggressive language
• •Replace "CRITICAL: You MUST..." with "Use X when..."
• •Excellent at parallel tool calls
• •May over-engineer — use <minimal_implementation>

Sonnet 4.5

• •Aggressive parallelism — may need <sequential_execution> for stability
• •Good balance of capability and efficiency
• •Strong at following structured XML prompts

Haiku 4.5

• •Keep prompts concise — smaller context window
• •Prioritize essential instructions
• •Good for simple, well-defined tasks