What is Structured Output?
Structured Output is the practice of making an LLM return data in a predictable machine-readable format such as JSON, XML, tables, or schema-constrained objects.
How It Works
Structured output is essential when LLM responses drive software rather than only human reading. It turns a free-form answer into data that can be parsed, validated, stored, routed, or used by another system. Reliable structured output usually requires clear schemas, examples, constrained decoding or JSON mode when available, validation, retries, and explicit handling of missing or uncertain fields. Without validation, superficially valid JSON can still contain wrong types, invalid enums, or unsupported claims.
Key Characteristics
- Produces machine-readable responses instead of only prose
- Often uses JSON, schema-constrained objects, tables, XML, or key-value records
- Requires validation because syntax correctness is not the same as semantic correctness
- Improves integration with APIs, workflows, databases, and automation
- Works best with explicit schemas, examples, retries, and error handling
Common Use Cases
- Extracting contract fields into JSON
- Classifying support tickets with fixed labels
- Returning tool arguments for an agent workflow
- Generating typed records for database insertion
- Validating LLM output before triggering automation
Example
Loading code...Frequently Asked Questions
Is valid JSON enough for structured output?
No. The output must also match the expected schema, types, enum values, business rules, and evidence requirements.
How can structured output be made more reliable?
Use schemas, constrained decoding or JSON mode, examples, validation, retries, and explicit null or missing-field handling.
When should structured output be used?
Use it whenever an LLM response will be consumed by code, stored in a database, routed to tools, or used in automation.
Can structured output prevent hallucinations?
No. It constrains format, not truth. Claims and extracted values still need validation against sources or business rules.