Structured data

Core Use Case

• Technique for generating structured data (JSON, Python code, bulleted lists) with no extra commentary
• Prevents Claude from adding headers, footers, or explanatory text around the requested content
• Critical for user experience when users need to copy/use raw output directly

The Problem

• Claude naturally wants to explain its work and add context
• When generating JSON, Claude often wraps it in markdown code blocks (backticks)
• Extra commentary makes it difficult for users to extract and use just the data they need

The Solution: Two-Part Approach

**1. Pre-fill an Assistant Message**

• Add a message as if Claude already started responding
• Include the opening marker (e. g. , JSON `)
• This signals to Claude it should continue from that point, not add a header

**2. Add a Stop Sequence**

• Define a sequence that tells Claude to stop generation immediately
• Use the closing marker (e. g. , `)
• Prevents Claude from adding footer commentary

How It Works Together

• Claude reads the user request and considers adding headers/footers
• Claude encounters the pre-filled assistant message and assumes it already started the response
• Claude generates only the core content (the JSON/data itself)
• Claude naturally tries to close the code block with the stop sequence
• Stop sequence triggers immediately, cutting off generation
• Result: only the raw structured data is returned

Practical Benefits

• Output can be directly copied and used without manual editing
• Works for any structured data format, not just JSON
• Removes need for post-processing to strip unwanted text
• Improves user experience in applications requiring clean data output

Takeaways

• Pre-fill an assistant message with the opening marker (e. g. , JSON `) to signal Claude should continue from that point rather than add headers
• Add a stop sequence at the closing marker (e. g. , `) to prevent Claude from adding footer commentary
• Together, these techniques generate only raw structured data with no extra explanation or markdown wrapping, making output directly usable without manual editing