State Validation and Integrity

Garbage In, Garbage Out. But in an agent, Garbage Out leads to an Infinite Loop.

Pydantic Validation

LangGraph integrates seamlessly with Pydantic.

from pydantic import BaseModel, Field

class AgentState(BaseModel):
    summary: str
    citation_count: int = Field(ge=0)  # Must be positive

# The Runtime automatically checks types on every step
def my_node(state: AgentState):
    # If we return this, the graph CRASHES with ValidationError
    return {"citation_count": -5}

Why Crash?

It is better to crash immediately with a clear ValidationError than to continue processing with invalid data that leads to silent hallucinations 10 steps later.