deepseek-ai/deepseek-harness · error · TypeError

tool execution arguments must be losslessly JSON-serializabl

Error message

tool execution arguments must be losslessly JSON-serializable

What it means

Error "tool execution arguments must be losslessly JSON-serializable" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/core/tools/src/index.ts:1414

      },
    }
    // Capture the finalizer BEFORE argument materialization: the
    // `finalizeContent` contract snapshots the callback when the call starts,
    // and an arguments getter can replace or clear the registered callback
    // during `snapshotJsonValue`. The collapse only decides whether the
    // CAPTURED callback is retained: the pre-dispatch abort path keeps it
    // (the cancellation contract routes aborted results through it — a getter
    // that aborts mid-materialization before an invalid-args failure lands in
    // the same retained path), while the `UNKNOWN_TOOL` denial and the
    // invalid-args failure of a NON-ABORTED collapsed call drop it (the call
    // could never execute).
    const capturedFinalizer = visible?.finalizeContent?.bind(visible)
    const finalizerFor = (): ToolDefinition['finalizeContent'] | undefined =>
      collapsed && !signal.aborted ? undefined : capturedFinalizer
    try {
      const detached = snapshotJsonValue(exec.arguments)
      if (detached === undefined) {
        throw new TypeError('tool execution arguments must be losslessly JSON-serializable')
      }
      const execution: MutableToolRunContext = { ...base, arguments: deepFreeze(detached) }
      this.deferredContexts.set(execution, deferredContexts)
      this.contentFinalizers.set(execution, finalizerFor())
      this.cancellationStates.set(execution, {
        callerSignal: signal,
        bodyInvoked: false,
      })
      if (collapsed) {
        // The collapse denies the call before the policy pipeline, but a
        // pre-dispatch abort still keeps the established cancellation
        // contract: `prepare`'s caller-cancellation check is skipped for
        // final-results, so honor the abort here instead of surfacing
        // `UNKNOWN_TOOL` on an already-cancelled call.
        if (signal.aborted) {
          return { kind: 'final-result', exec: execution, result: toolAbortedBeforeDispatchResult() }
        }
        // The name IS visible here, so the denial carries the route the model

View on GitHub (pinned to b150a551b8)

When it happens

Trigger: Thrown at packages/core/tools/src/index.ts:1414 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/00f32c54a8ea335e. Report an issue: GitHub.