# Running single Flow steps

With the **Run flow step** button which is shown below the step's name you can run the current step without running the entire flow:

![](/files/-MjULtVLdT_vLdFdgM5_)

The flow step will then be executed and the debugger output will be shown directly in the flow builder:

![](/files/-MjULTxe3kM12wCIGckK)

The example above also uses references to other parts of the flow (`{{ start_date }}` and `{{ end_date }}`):

![](/files/-MjUMdsecA1uRmn520hf)

In order to run the **Summary Report** step, both referenced steps have to be run at some point before, e.g. as part of a regular flow run or through **Run flow step**.

{% hint style="warning" %}
The referenced steps need to be available as per [flow run data retention](/automation/flow-builder/flow-run-data-retention-and-logging.md) setting of the flow.\
E.g. if the flow ran for the last time 5 days ago and the flow run data retention setting on the flow is 2 days, **Run flow step** would not work, as the output for the referenced steps are not available.
{% endhint %}

The flow is always saved before running a flow step, thus the flow needs to be in a state where it can be saved (i.e. all connectors need to be connected, only one starting point, etc.).

## Special Cases

### Looper

When using **Run flow step** on a Looper, all steps within the looper will be run.\
The output shown will be the output of the Looper itself (i.e. a list of the Looper's results).

When running a flow step inside an action loop, the reference to the looper will not be the Looper's input (as it is the case in a regular flow run), but rather the Looper's output. Thus, testing those steps will not result in the same outcome as a regular flow run. \
Instead we recommend to run the Looper that the step is referencing.

When the `index` variable is used in a step that is being run, `index` it will be replaced by `0`.

### Mail Sender

This functionality is currently not available for the [Mail Sender](/connectors/helpers/mail-helper.md) and will return an error instead.


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