PowerShell Verbose and diagnostic streams

PowerShell separates ordinary data from diagnostic and informational messages by using numbered streams. The success stream is stream 1, errors are stream 2, warnings stream 3, verbose stream 4, debug stream 5, and information stream 6.

Lesson 2 min read Windows PowerShell 5.1 and PowerShell 7

Documentation: Microsoft Learn

Written and tested by Dhrub Bharali · Updated 02 October 2026

Overview

Write-Verbose and Write-Debug are intended for diagnostics and are normally gated by -Verbose and -Debug. Write-Information writes to stream 6 and can carry strings or objects. Since Windows PowerShell 5.0, Write-Host is implemented on the information stream as well, so its messages can be redirected or captured with information-stream redirection. The important distinction is that Write-Host is still not ordinary success-stream output: a function should not use it as the data contract that callers are expected to pipe, filter, sort, or export.

For reusable functions, emit result objects on the success stream and reserve verbose, debug, warning, error, and information messages for commentary about the operation. That gives the caller control over what to display, suppress, redirect, or log.

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function Show-Streams {
    [CmdletBinding()]
    param()
Write-Output 'Output: the only stream that goes down the pipeline'
Write-Verbose 'Verbose: hidden unless -Verbose is passed'
Write-Warning 'Warning: shown by default, not part of output'
}
Show-Streams -Verbose

Stage 1function-Verbose

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function Show-Streams {
    [CmdletBinding()]
    param()
Write-Output 'Output: the only stream that goes down the pipeline'
Write-Verbose 'Verbose: hidden unless -Verbose is passed'
Write-Warning 'Warning: shown by default, not part of output'
}
Show-Streams -Verbose

What happens

The function writes to three streams. Called with -Verbose, all three appear, and the verbose line is prefixed with VERBOSE: while the warning is prefixed WARNING:. Drop -Verbose and the verbose line vanishes while the other two stay. Only the Write-Output line would survive being assigned to a variable.

Worth remembering

Success-stream objects are the normal pipeline data; diagnostic and informational messages use separate streams.
Write-Verbose and Write-Debug are opt-in diagnostics controlled by -Verbose and -Debug.
Since Windows PowerShell 5.0, Write-Host uses the information stream and can be redirected or captured separately; it is still not a substitute for returning result objects on stream 1.
Design functions so callers can choose independently what data to consume and what diagnostics to display or log.

Primary documentation

PowerShell objects and pipelines documentation

Try it

Illustrative output · values vary by environment

1PS> function Show-Streams {

2PS> [CmdletBinding()]

3PS> param()

4PS> Write-Output 'Output: the only stream that goes down the pipeline'

5PS> Write-Verbose 'Verbose: hidden unless -Verbose is passed'

6PS> Write-Warning 'Warning: shown by default, not part of output'

7PS> }

8PS> Show-Streams -Verbose

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function Show-Streams {
    [CmdletBinding()]
    param()
    Write-Output 'Output: the only stream that goes down the pipeline'
    Write-Verbose 'Verbose: hidden unless -Verbose is passed'
    Write-Warning 'Warning: shown by default, not part of output'
}
Show-Streams -Verbose

Ready to inspect.

Writes to three different streams so you can see which ones appear.

Show reference output

Illustrative output · values vary by environment

Output: the only stream that goes down the pipeline
VERBOSE: Verbose: hidden unless -Verbose is passed
WARNING: Warning: shown by default, not part of output

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Inspect warning diagnostics

Return Id and Message for Warning-level events.

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