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When a LangGraph agent repeats a tool call, inspect the graph transitions and state at the first repeated cycle before changing the model or raising a limit. The cause is usually a route that never reaches a terminal node, an unbounded retry, or state that keeps a continuation condition true. A checkpoint resume can also replay a node, so external actions need protection against duplicates.

Find the first repeated transition

Reproduce the run and identify the node and tool invocation that repeat. Then inspect the transitions and relevant state values around the first repetition. A trace can show whether the graph is cycling through the same route, retrying after an error, or making progress with a workflow that simply needs more steps.

  1. Record the repeated node or tool and the state values that determine its next route.
  2. Follow the graph edges, conditional routing, and any Command destinations until the expected terminal branch.
  3. Check whether that branch is reachable and whether each iteration changes the state used by its condition.
  4. Only after identifying the cause, change the route, retry behavior, state update, or limit.

Optional LangSmith tracing can help inspect execution behavior; it is not a substitute for checking the graph’s routing and state.

Check for a cycle or missing terminal route

GRAPH_RECURSION_LIMIT means a StateGraph reached its maximum number of steps before hitting a stop condition. An unintended cycle is a common cause, though a complex workflow may legitimately need many iterations. See the official error guidance.

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A graph needs a reachable way to finish. Use END or an explicit done node, and make each conditional route’s destinations and conditions clear. For example, if a count controls completion, confirm that it advances and that the condition routes to the done branch once the threshold is reached. Increasing the limit does not make an unreachable terminal route reachable.

Bound error recovery and retries

A tool result returning to the agent is not necessarily a bug: the model may need to interpret the result, choose another tool, or recover from an error. LangGraph’s Thinking in LangGraph documentation demonstrates returning actionable tool-error context so the agent can decide what to do next. It also distinguishes recoverable errors from cases that should be surfaced or handled another way.

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For every retry path, define what changes and when to stop. Retry a transient failure only under an explicit attempt bound or other stopping rule. If the error cannot be resolved by another attempt, route to recovery, request human input, or surface the failure instead of sending the same unchanged input back through the same path indefinitely.

Verify state updates and reducer behavior

State updates may merge or accumulate rather than replace existing values. A value that looks empty in a node’s update does not necessarily clear the accumulated state: with a reducer, an empty list can leave prior values in place. Inspect the relevant field’s reducer and the state after each transition, especially for counters, messages, and errors. Use overwrite semantics when the intended update is replacement. The Graph API overview documents reducers and state updates.

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Then verify that the condition controlling continuation reads the field you expect and can become false. If the condition depends on a counter that never advances, a stale error, or an accumulated list that is not cleared, fix the update or the condition rather than raising the step limit.

Protect side effects from checkpoint replay

Graph control flow can call a tool repeatedly during one run; checkpoint recovery is a separate issue. A node interrupted or resumed from a checkpoint can run again from its beginning, potentially repeating an external action even if the earlier attempt already took effect. Do not rely on the graph to guarantee exactly-once external effects.

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Make side-effecting operations safe to replay where possible: use idempotency keys, upserts, or read-before-write checks. The Graph API documentation discusses checkpointing and idempotency. These protections address duplicate effects; they do not fix a routing loop.

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Choose a fix that matches the cause

Cause Correction Trade-off or check
Cycle or unreachable terminal route Repair the edge or conditional branch; make END or a done node reachable. Verify the branch condition can become true from actual state changes.
Error recovery with no stopping rule or changed input Bound attempts, change the recovery path, or surface the error for human handling. Retry only when another attempt can plausibly change the outcome.
Stale or accumulated state Correct the reducer or use overwrite semantics where replacement is intended. Inspect state after each update, not just the value returned by a node.
Checkpoint replay of a side effect Use idempotency keys, upserts, or read-before-write checks. This prevents duplicate external effects; it does not terminate a control-flow cycle.

Raise recursion_limit only for a deeper valid workflow

After confirming the routes, stop conditions, retry rules, and state progress are correct, increase recursion_limit only if the workflow is genuinely expected to take more steps. The setting can allow a legitimate long-running graph to finish, but it also lets an accidental cycle run longer before the guard triggers. The official recursion-limit guidance describes the setting; this article does not specify a numeric default because defaults can vary by version.

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