langchain-ai/langgraph · error · TypeError

Invalid checkpointer provided. Expected an instance of `Base

Error message

Invalid checkpointer provided. Expected an instance of `BaseCheckpointSaver`, `True`, `False`, or `None`. Received {type}. Pass a proper saver (e.g., InMemorySaver, AsyncPostgresSaver).

What it means

Error "Invalid checkpointer provided. Expected an instance of `BaseCheckpointSaver`, `True`, `False`, or `None`. Received {type}. Pass a proper saver (e.g., InMemorySaver, AsyncPostgresSaver)." thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/types.py:113

"""

All = Literal["*"]
"""Special value to indicate that graph should interrupt on all nodes."""

Checkpointer = None | bool | BaseCheckpointSaver
"""Type of the checkpointer to use for a subgraph.

- `True` enables persistent checkpointing for this subgraph.
- `False` disables checkpointing, even if the parent graph has a checkpointer.
- `None` inherits checkpointer from the parent graph.
"""


def ensure_valid_checkpointer(checkpointer: Checkpointer) -> Checkpointer:
    if checkpointer not in (None, True, False) and not isinstance(
        checkpointer, BaseCheckpointSaver
    ):
        raise TypeError(
            "Invalid checkpointer provided. Expected an instance of "
            "`BaseCheckpointSaver`, `True`, `False`, or `None`. "
            f"Received {type(checkpointer).__name__!s}. "
            "Pass a proper saver (e.g., InMemorySaver, AsyncPostgresSaver)."
        )
    return checkpointer


StreamMode = Literal[
    "values", "updates", "checkpoints", "tasks", "debug", "messages", "custom"
]
"""How the stream method should emit outputs.

- `"values"`: Emit all values in the state after each step, including interrupts.
    When used with functional API, values are emitted once at the end of the workflow.
- `"updates"`: Emit only the node or task names and updates returned by the nodes or tasks after each step.
    If multiple updates are made in the same step (e.g. multiple nodes are run) then those updates are emitted separately.
- `"custom"`: Emit custom data using from inside nodes or tasks using `StreamWriter`.

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/types.py:113 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/e32d59dc9c8eb4ab. Report an issue: GitHub.