StateGraph is the primary builder for creating LangGraph applications. It provides a structured, high-level interface for defining a graph’s nodes, edges, and shared state before the graph is compiled into an executable runtime.

State Schema

A StateGraph is parameterized by a state schema, typically a TypedDict which defines the data shared across all nodes. This schema acts as a contract, enforcing type safety and making it explicit what information is available at each step of execution.

Graph Construction

Graph structure is defined declaratively. You register work units using add_node(), connect them with add_edge() for fixed transitions, and use add_conditional_edges() to enable dynamic routing based on state or function outputs.

Compilation and Runtime

Before execution, the graph must be finalized with compile(), which validates the structure, builds the underlying Pregel runtime, and optionally configures persistence via checkpointers and stores. A StateGraph itself is never executed directly—it exists solely to produce a CompiledStateGraph that can be run.

Execution Flow and Maintainability

This builder pattern cleanly separates graph construction from execution, making workflows easier to reason about, test, and modify. Entry points are defined with set_entry_point(), and terminal nodes connect to the special END node to signal completion. The result is a readable, maintainable way to express complex agent logic without embedding control flow directly in code.

Walkthrough