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Editorial Team
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Asked: 2026-05-23T00:35:49+00:00

Is there a way in C# to see if a string is Base 64

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Is there a way in C# to see if a string is Base 64 encoded other than just trying to convert it and see if there is an error? I have code code like this:

// Convert base64-encoded hash value into a byte array.
byte[] HashBytes = Convert.FromBase64String(Value);

I want to avoid the "Invalid character in a Base-64 string" exception that happens if the value is not valid base 64 string. I want to just check and return false instead of handling an exception because I expect that sometimes this value is not going to be a base 64 string. Is there some way to check before using the Convert.FromBase64String function?

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1 Answer

  1. Editorial Team

    Update: For newer versions of C#, there’s a much better alternative, please refer to the answer by Tomas here: https://stackoverflow.com/a/54143400/125981.

    It’s pretty easy to recognize a Base64 string, as it will only be composed of characters 'A'..'Z', 'a'..'z', '0'..'9', '+', '/' and it is often padded at the end with up to three ‘=’, to make the length a multiple of 4. But instead of comparing these, you’d be better off ignoring the exception, if it occurs.

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