microsoft/semantic-kernel · error · KernelException

The step {this.Name} has more than one function, so a functi

Error message

The step {this.Name} has more than one function, so a function name must be provided.

What it means

Thrown by ProcessStepBuilder.ResolveFunctionName when the step has more than one kernel function but no explicit function name was provided. Auto-resolution only works when there is exactly one function to choose from; with multiple functions, ambiguity must be resolved by the caller.

Source

Thrown at dotnet/src/Experimental/Process.Core/ProcessStepBuilder.cs:137

        // Register the group by GroupId.
        this.IncomingEdgeGroups[edgeGroup.GroupId] = edgeGroup;
    }

    /// <summary>
    /// Resolves the function name for the step.
    /// </summary>
    /// <returns></returns>
    /// <exception cref="KernelException"></exception>
    private string ResolveFunctionName()
    {
        if (this.FunctionsDict.Count == 0)
        {
            throw new KernelException($"The step {this.Name} has no functions.");
        }
        else if (this.FunctionsDict.Count > 1)
        {
            throw new KernelException($"The step {this.Name} has more than one function, so a function name must be provided.");
        }

        return this.FunctionsDict.Keys.First();
    }

    /// <summary>
    /// Links the output of the current step to the an input of another step via the specified event type.
    /// </summary>
    /// <param name="eventId">The Id of the event.</param>
    /// <param name="edgeBuilder">The targeted function.</param>
    internal virtual void LinkTo(string eventId, ProcessStepEdgeBuilder edgeBuilder)
    {
        if (!this.Edges.TryGetValue(eventId, out List<ProcessStepEdgeBuilder>? edges) || edges == null)
        {
            edges = [];
            this.Edges[eventId] = edges;
        }

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Specify the function name explicitly when creating the target: step.OnFunction("FunctionName").SendEventTo(target).
2. Use WhereInputEventIs or OnFunction with the specific function name to disambiguate.
3. If only one function should be the target, remove or rename the other [KernelFunction] methods on the step.

Example fix

// before — step has two functions, no name specified
process.OnInputEvent("Start")
    .SendEventTo(myStep.AsFunctionTarget()); // throws — ambiguous

// after — specify the function name
process.OnInputEvent("Start")
    .SendEventTo(myStep.OnFunction("ProcessData"));

if (step.FunctionsDict.Count > 1 && string.IsNullOrWhiteSpace(functionName))
    throw new InvalidOperationException(
        $"Step '{step.Name}' has {step.FunctionsDict.Count} functions. Specify a function name.");

// proceed with resolution

bool NeedsExplicitFunctionName(ProcessStepBuilder step) => step.FunctionsDict.Count > 1;

When it happens

Trigger: Calling an API that resolves a function target on a step with multiple [KernelFunction] methods, without specifying which function to target. E.g. edge.SendEventTo(step.AsFunctionTarget()) where step has multiple functions.

Common situations: Adding a step with several kernel functions and then using a convenience method that auto-resolves the function; refactoring a single-function step to add a second function without updating edge definitions; using generic targeting APIs that assume single-function steps.

Related errors

• The step {this.Name} has no functions.
• The target step has more than one function, so a function na
• The target step {this.Name} has no functions.
• The function {functionName} does not exist on step {this.Nam
• Type '{stepType.FullName}' must be a subclass of KernelProce

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/b30ac812c3ce0528. Report an issue: GitHub.