Structured data exercise

Problem

• Generate three AWS CLI commands in a single response with no additional commentary or explanation
• Use only message prefilling and stop sequences (no prompt modification)

Solution Approach

Step 1: Initial Prefilling

• Add an assistant message prefilled with three backticks (`) to skip initial commentary
• Add a stop sequence of three backticks to end output at the right place
• Result: Gets three commands but includes unwanted "bash" language identifier

Step 2: Refine Prefilling

• Include "bash" in the prefilled message (`bash) to explicitly indicate markdown code block
• This tells Claude it's writing bash-formatted commands
• Prevents Claude from auto-adding the language identifier

Step 3: Advanced Prefilling

• Use message prefilling to guide Claude's behavior beyond just syntax markers
• Add descriptive text like "here are all three commands in a single block without any comments:" before the code block
• This dramatically improves reliability and prevents unwanted bash comments

Key Insights

• Message prefilling is not limited to special characters—you can include full instructional text
• Prefilling helps Claude understand the desired format and reduces unwanted additions
• Stop sequences work best when combined with strategic prefilling
• Explicit formatting guidance in prefilled messages produces more consistent results

Takeaways

• Message prefilling can include full instructional text, not just syntax markers, to guide Claude's behavior and format
• Combining prefilling with stop sequences effectively controls output boundaries and prevents unwanted additions
• Explicitly indicating the code block format (`bash) in the prefilled message prevents Claude from auto-adding language identifiers
• Strategic prefilling that describes the desired output (e. g. , "here are all three commands in a single block without any comments") dramatically improves reliability