# Sniff Test tool

The Sniff Test displays data as it travels from one step to another in the stream. The Sniff Test is designed to be used as a supplement to logs so that you can debug complex situations.

**Note:** Applying a Sniff Test slows transformation run speed, so use with care.

To use this, complete these steps:

1. Right-click a step in the transformation as it runs.
2. Select **Sniff Test During Execution**.

   There are three options in this menu:

   * **Sniff test input rows** - Shows the data inputted into the step.
   * **Sniff test output rows** - Shows the data outputted from the step.
   * **Sniff test error handling** - Shows error handling data.

After you have selected an option, values in the data stream appear. You are also able to observe throughput.


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