microsoft/semantic-kernel · error · KernelException

The process named '{this.Name}' does not expose an event wit

Error message

The process named '{this.Name}' does not expose an event with Id '{eventId}'.

What it means

Thrown by ProcessBuilder.WhereInputEventIs when the given eventId is not found in the process's _externalEventTargetMap. This means the process has no step registered to receive an external event with that Id, so no target can be resolved.

Source

Thrown at dotnet/src/Experimental/Process.Core/ProcessBuilder.cs:500

    /// <returns></returns>
    internal ListenForBuilder ListenFor()
    {
        return new ListenForBuilder(this);
    }

    /// <summary>
    /// Retrieves the target for a given external event. The step associated with the target is the process itself (this).
    /// </summary>
    /// <param name="eventId">The Id of the event</param>
    /// <returns>An instance of <see cref="ProcessFunctionTargetBuilder"/></returns>
    /// <exception cref="KernelException"></exception>
    public ProcessFunctionTargetBuilder WhereInputEventIs(string eventId)
    {
        Verify.NotNullOrWhiteSpace(eventId, nameof(eventId));

        if (!this._externalEventTargetMap.TryGetValue(eventId, out var target))
        {
            throw new KernelException($"The process named '{this.Name}' does not expose an event with Id '{eventId}'.");
        }

        if (target is not ProcessFunctionTargetBuilder functionTargetBuilder)
        {
            throw new KernelException($"The process named '{this.Name}' does not expose an event with Id '{eventId}'.");
        }

        // Targets for external events on a process should be scoped to the process itself rather than the step inside the process.
        var processTarget = functionTargetBuilder with { Step = this, TargetEventId = eventId };
        return processTarget;
    }

    /// <summary>
    /// Builds the process.
    /// </summary>
    /// <returns>An instance of <see cref="KernelProcess"/></returns>
    public KernelProcess Build(KernelProcessStateMetadata? stateMetadata = null)
    {

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Ensure a step in the process has been wired to handle the event using process.OnInputEvent(eventId).SendEventTo(target) before calling WhereInputEventIs.
2. Verify the eventId string exactly matches the one used when registering the input event (case-sensitive).
3. Check that the step targeted by the event is added to the process before WhereInputEventIs is called.

Example fix

// before
var target = process.WhereInputEventIs("StartEvent"); // throws if no step registered for StartEvent

// after — register the edge first
process.OnInputEvent("StartEvent").SendEventTo(myStep.WhereInputEventIs("input"));
var target = process.WhereInputEventIs("StartEvent");

var registeredEvents = process.GetExternalEvents(); // hypothetical or reflection
if (!registeredEvents.Contains(eventId))
    throw new InvalidOperationException(
        $"Event '{eventId}' is not registered. Call process.OnInputEvent(\"{eventId}\").SendEventTo(...) first.");

var target = process.WhereInputEventIs(eventId);

try
{
    var target = process.WhereInputEventIs(eventId);
}
catch (KernelException ex) when (ex.Message.Contains("does not expose an event"))
{
    // Handle: event not registered — log and register or skip
    logger.LogWarning("External event {EventId} not found on process", eventId);
}

When it happens

Trigger: Calling process.WhereInputEventIs("myEvent") before any step has been wired to respond to that event via OnInputEvent; using an event Id that was never registered; misspelling the event Id; calling WhereInputEventIs on a freshly constructed process with no edges defined.

Common situations: Defining a process and trying to reference an external event before building the edge graph; event Id mismatch between the publisher and the process definition; refactoring step names or event Ids and forgetting to update the external event reference.

Related errors

• Unsupported thread type: {typeof(T).Name}
• Map operation is not a process.
• Entry agent is not defined.
• Unable to transform output to {typeof(TOutput)}.
• Unable to transform result into {typeof(TOutput).Name}

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/e0a0de8ec6c5d693. Report an issue: GitHub.