Eval Library
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For LangChainAI Platform

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.

Employees

~200

Industry

Agent Framework

Headquarters

San Francisco, CA

Sample tests· showing 3 of 9

#InputExpected behaviorCheck
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

Recommended for

LangChain (+ LangGraph)LangChain customers

Works with

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