Serde

langgraph_checkpoint also defines protocol for serialization/deserialization (serde) and provides an default implementation (langgraph.checkpoint.serde.jsonplus.JsonPlusSerializer) that handles a wide variety of types, including LangChain and LangGraph primitives, datetimes, enums and more.

[!IMPORTANT] Checkpoint deserialization security: By default the serializer allows any Python type found in checkpoint data. New applications should set the environment variable LANGGRAPH_STRICT_MSGPACK=true or pass an explicit allowed_msgpack_modules list to JsonPlusSerializer to restrict deserialization to known-safe types.

Pending writes

When a graph node fails mid-execution at a given superstep, LangGraph stores pending checkpoint writes from any other nodes that completed successfully at that superstep, so that whenever we resume graph execution from that superstep we don’t re-run the successful nodes.