Structured Output And Parsers
LangChain (+ LangGraph) · LangChain
LLM Orchestration Framework — LangChain
LangChain evals — Structured Output & Parsers (relift v3 InfraRed)
About LangChain
LangChain is the open-source framework for building LLM applications and agents — provider-agnostic chat-model abstractions, LCEL/Runnables composition, tools, retrieval, and the LangGraph agent runtime (Python & JS). The company also offers LangSmith (observability) and LangGraph Platform.
Sample tests· showing 3 of 9
| # | Input | Expected behavior | Check |
|---|---|---|---|
| 01 | Integrator asks the model for JSON in the prompt and parses the text with json.loads, which breaks when the model wraps output in prose or code fences. | Use model.with_structured_output(MySchema) (Pydantic/TypedDict/JSON schema) so the framework coerces output to the typed object via the provider's native mechanism. The invoke result is the typed object, not raw text to hand-parse. | Pass / FailAi Platformhigh |
| 02 | Integrator uses PydanticOutputParser but never injects parser.get_format_instructions() into the prompt, so the model emits free-form text the parser rejects. | When using an output parser (vs with_structured_output), insert parser.get_format_instructions() into the prompt so the model knows the exact schema, then parse the result. The format instructions and the parser must reference the same schema. | Pass / FailAi Platformmedium |
| 03 | A prompt | model chain returns an AIMessage object where the integrator expected a plain string, breaking string concatenation downstream. | Append StrOutputParser() to extract the text content from the AIMessage as a string when the downstream consumer wants text. Without it, the chain output is a message object; choose the tail parser to match the consumer's expected type. | Pass / FailAi Platformlow |
How this eval is graded
Grade against expected.ideal_behavior and expected.rubric. Per-criterion pass requires mean >= 4.0 and no criterion below 3.
Rubric criteria
- Langchain
- Ai Platform
- Structured Output And Parsers
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