{"head":{"title":"What Is Structured Output in LLMs? Definition | OceanLab","description":"Structured output makes a language model reply in a fixed format, such as JSON matching a schema, so code can use it. How it works and common mistakes.","canonical":"https://oceanlab.in/glossary/structured-output"},"crumbs":[{"name":"Home","path":"/"},{"name":"Glossary","path":"/glossary"},{"name":"structured output","path":"/glossary/structured-output"}],"slug":"structured-output","term":"Structured output","aka":["JSON mode","constrained decoding"],"category":"AI building blocks","short":"Getting a language model to reply in a fixed, machine-readable format, such as JSON that matches a schema you define.","body":[["Instead of free text, you give the model a schema, for example an object with an invoice number, a date and a list of line items, and ask for a reply that fits it. Many APIs can enforce the schema while the reply is generated, so the result always parses."],["Valid format is not the same as correct content. A reply can match the schema perfectly and still have the wrong date in it, so values still need checks."]],"why":["Most business uses of an ",{"href":"/glossary/llm","text":"LLM"}," end in a system, not a person: a database row, a form, an API call. Structured output removes fragile text parsing and makes results easy to validate, store and test with ",{"href":"/glossary/llm-evals","text":"evals"},"."],"example":["An accounts team extracts invoices from PDFs into a schema with supplier, invoice number, due date, currency and line items. Any invoice where the line items do not add up to the total goes to a person instead of straight into the ledger."],"inBuild":null,"mistakes":[["Skipping value checks because the JSON is valid."],["Making every field required, which pushes the model to invent values. Allow null for missing data."],["Huge, deeply nested schemas. Smaller schemas are easier for the model and for reviewers."]],"related":[{"href":"/glossary/tool-calling","label":"Tool calling (function calling)","detail":"A way for a language model to ask your application to run a defined function and give it the result."},{"href":"/glossary/llm-evals","label":"LLM evals (evaluations)","detail":"Repeatable tests that score how well a model, prompt or AI feature does a specific task."},{"href":"/glossary/hallucination","label":"Hallucination (AI)","detail":"When an AI model produces information that is false or made up, presented as if it were true."},{"href":"/glossary/temperature","label":"Temperature (LLM setting)","detail":"A setting that controls how random a language model's output is: lower is more predictable, higher is more varied."}],"tools":[{"href":"/tools/llm-api-cost-calculator","label":"LLM API cost calculator","detail":"Free tool"}],"links":[{"href":"/ai-automation","label":"AI automation","detail":"How OceanLab automates company workflows with AI."},{"href":"/ai","label":"AI by industry","detail":"AI use cases, costs and risks per industry."}],"sources":[],"legal":false,"updatedAt":"2026-10-25"}