PowerShell Base64 Decode & Encode

How Do You Base64 Encode a String in PowerShell?

Use [System.Convert]::ToBase64String() combined with [System.Text.Encoding]::UTF8.GetBytes() to encode any string to Base64. PowerShell has full access to the .NET framework, so the same System.Convert class used in C# is available directly.

# Encode a string to Base64
$text = "Hello World"
$bytes = [System.Text.Encoding]::UTF8.GetBytes($text)
$encoded = [System.Convert]::ToBase64String($bytes)
Write-Output $encoded
# Output: SGVsbG8gV29ybGQ=

Always specify [System.Text.Encoding]::UTF8 explicitly rather than relying on the system default encoding. The default encoding varies between Windows versions and locales, which can produce inconsistent output across machines. The result uses the standard Base64 alphabet (A-Z, a-z, 0-9, +, /) with = padding as defined in RFC 4648. For a browser-based alternative, use the Base64 text encoder.

How Do You Decode Base64 in PowerShell?

Use [System.Convert]::FromBase64String() to convert a Base64 string back to a byte array, then [System.Text.Encoding]::UTF8.GetString() to reconstruct the original text. The FromBase64String() method validates the input and throws System.FormatException if the string contains invalid characters or malformed padding.

# Decode a Base64 string
$encoded = "SGVsbG8gV29ybGQ="
$bytes = [System.Convert]::FromBase64String($encoded)
$decoded = [System.Text.Encoding]::UTF8.GetString($bytes)
Write-Output $decoded
# Output: Hello World

Wrap decoding in a try/catch block in production scripts to handle malformed input gracefully. Invalid Base64 input — such as strings with incorrect padding or characters outside the Base64 alphabet — causes an exception rather than silently returning garbage data. To decode Base64 directly in your browser, use the Base64 text decoder.

How Do You Encode a File to Base64 in PowerShell?

Use [Convert]::ToBase64String() with [IO.File]::ReadAllBytes() to encode a binary file to Base64 in a single line. This loads the entire file into memory, so it works best for files that fit within available RAM. For large files, use a stream-based approach.

# Encode a file to Base64
$filePath = "C:path	oile.png"
$fileBytes = [IO.File]::ReadAllBytes($filePath)
$encoded = [Convert]::ToBase64String($fileBytes)
Write-Output $encoded

# Save the Base64 output to a text file
$encoded | Out-File -FilePath "C:path	oile.b64" -NoNewline -Encoding ascii

# Create a data URI for HTML embedding
$dataUri = "data:image/png;base64," + $encoded
Write-Output $dataUri

The -NoNewline flag on Out-File prevents PowerShell from appending a trailing newline, which would corrupt the Base64 string. Specify -Encoding ascii to avoid the UTF-16 BOM that PowerShell writes by default. The Base64 file encoder performs this same operation in your browser without uploading the file to any server.

How Do You Use Base64 for Basic Auth in PowerShell?

HTTP Basic Authentication encodes credentials as username:password in Base64 and sends them in the Authorization header. PowerShell's Invoke-RestMethod and Invoke-WebRequest cmdlets accept custom headers, so you can construct a Basic Auth header manually using [Convert]::ToBase64String().

# Build a Basic Auth header
$credentials = "user:password"
$bytes = [Text.Encoding]::UTF8.GetBytes($credentials)
$b64 = [Convert]::ToBase64String($bytes)
$headers = @{ Authorization = "Basic $b64" }

# Use with Invoke-RestMethod
$response = Invoke-RestMethod -Uri "https://api.example.com/data" -Headers $headers -Method Get
Write-Output $response

# One-liner version
$response = Invoke-RestMethod -Uri "https://api.example.com/data" -Method Get \    -Headers @{ Authorization = "Basic " + [Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("user:password")) }

Never hardcode credentials in scripts that are committed to version control. Use Get-Credential to prompt for credentials at runtime, or store secrets in environment variables or a secrets manager. PowerShell 7+ supports -Credential on many cmdlets which handles the encoding automatically. For understanding the encoding format, see the What is Base64 guide.

PowerShell vs Terminal Base64 Commands

Base64 encoding commands differ significantly across platforms. The table below compares the syntax for encoding a string on PowerShell (Windows), Linux bash, and macOS Terminal, which helps when writing cross-platform scripts or documentation.

Note that Linux uses -d and macOS uses -D for decoding — a common source of script portability issues. PowerShell Core (version 7+) runs identically on Windows, Linux, and macOS, making it a reliable choice for cross-platform automation. For Linux-specific commands, see the Base64 in Linux guide. For macOS, see the Base64 on macOS guide.

Frequently Asked Questions

Related Base64 Tools and Guides

• What is Base64? - Comprehensive guide to the Base64 encoding format
• Base64 Text Encoder - Encode text to Base64 in your browser
• Base64 Text Decoder - Decode Base64 strings in your browser
• Base64 in C# - Use the same System.Convert methods in C# and .NET
• Base64 in Linux - Command-line Base64 encoding on Linux
• Base64 on macOS - Base64 commands for macOS Terminal
• Base64 File Encoder - Encode files to Base64 client-side
• All Base64 Tools - Browse the complete toolset