# Events

> Events capture what happens during process execution. In BPMN, events are grouped into three main types: **Start**, **Intermediate**, and **End** events. These can behave as either *catching* events (which react to a trigger) or *throwing* events (which send a trigger).

Events capture what happens during process execution. In BPMN, events are grouped into three main types: **Start**, **Intermediate**, and **End** events. These can behave as either *catching* events (which react to a trigger) or *throwing* events (which send a trigger).

## Start events

Start events define how a process begins. They are always catching events and can be triggered manually, by a message, or on a schedule.

* **None** — starts the process when manually triggered or started via Orchestrator.
* **Message events** — triggered by an event from Integration Service.

  ![Message start event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-message-start-event-properties-589229-593840aa.webp)

* **Timer events** — start the process on a schedule or delay. A **Timer start event** begins a process based on a defined schedule rather than user or system input. Configure it using the **Timer** section, which supports **Date**, **Duration**, or **Cycle** types. For recurring executions, use **Cycle** and specify the **Repeat** frequency (for example, hourly or daily). The **At** and **Repetitions** fields provide additional control over timing and limits. In the **Implementation** section, set the **Action** to **None** if no inbound event is required, or to **Wait for connector event** if the process should listen for an external trigger before proceeding. Timer start events are ideal for scheduled automations such as hourly syncs or daily reports. Read more in [Integration Service connectors](https://docs.uipath.com/integration-service/automation-cloud/latest/user-guide/connectors).

  ![Timer start event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-timer-start-event-properties-589233-f02ac565.webp)

## Intermediate events

Intermediate events represent something that happens between the start and end of a process. They can delay flow, wait for input, handle errors, or signal other activities.

**Intermediate catching events** wait for a message, timer, or API trigger during execution. The process pauses until the trigger occurs.

**Boundary events** are a special type of intermediate catching event attached to a task. They can be configured as follows:
* **Interrupting boundary events** — cancel the attached task when triggered (for example, by a **Timer** or **Message**).

   **Timer boundary event:** Interrupts a task if it runs too long. Configure a **Duration**, specific **Date**, or recurring **Cycle**. The **Value** field accepts ISO 8601 durations (e.g., `PT1H` for one hour). When the timer expires, the process continues along the boundary event path.

   The **Implementation** section can include actions such as logging or retries, though it’s commonly left as **None**.

  ![Timer boundary event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-timer-boundary-event-properties-589197-eb787cd9.webp)

   **Message boundary event:** Listens for a specific message while the task runs. When received, it interrupts the task and diverts flow along a new path. 
   
   Define message handling logic in the **Implementation** section (for example, **Wait for connector event** or **External input**). Use the **Inputs** and **Outputs** sections to pass or extract data, or **Update variables** to modify process data dynamically.

  ![Message boundary event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-message-boundary-event-properties-589208-9d393948.webp)

* **Non-interrupting boundary events** — trigger a parallel path while allowing the task to continue running. Can be **Timer** or **Message** based.
* **Error boundary events** — handle errors thrown by the attached activity. By default, the **Exception** is set to **Catch all**, meaning it captures any unhandled error. This path usually acts as a fallback or recovery route.

  ![Error boundary event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-error-boundary-event-properties-589191-1e258347.webp)

**Intermediate throwing events** actively send a trigger. For example, a **Message intermediate throwing event** acts like a **Send task**, invoking an Integration Service API execution.

## End events

End events mark the completion of a process path and behave as throwing events. They may end the workflow normally, send data outward, or terminate all active paths.

* **Error end event** — completes the process instance and faults the Orchestration Runtime (OR) job.
* **Message end event** — sends a message when the process concludes. You can configure it to execute a connector activity (for example, Slack, Salesforce, or ServiceNow) using the **Execute connector activity** implementation. 

  Select the target **Connector**, define the **Connection**, and choose the **Activity** to run. Inputs pass data to the connector, while Outputs capture and store responses for use in later steps.

  ![Message end event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-message-end-event-properties-589212-634327d1.webp)

* **Terminate end event** — cancels all other execution paths, especially in parallel flows. It marks the complete conclusion of a process. 

  Optionally, you can define an **Implementation action** to execute a connector operation, return data, or trigger a follow-up system. If no action is needed, set it to **None**. 
  
  Use the **Arguments** section to define output values that can be passed to parent processes or used for reporting.

  ![End event properties](https://dev-assets.cms.uipath.com/assets/images/maestro/maestro-end-event-properties-589221-6917a0af.webp)