You can encode/decode base64 using javascript in NeoLoad: You can find attached a Javascript library file to encode/decode base64. In NeoLoad, select edit > JS Library > New JS Library. Create a new JS library, select use an existing library file and pick the attached Base64.js file. You can name it something like "Base64". Then you are able to use Base64.encode("my value to encode"); in a NeoLoad JS action: In your virtual user profile, insert a JavaScript action where you want to encode/decode a value or string to base64. It could be after an extraction or declared variable, but before where the value is used and encoded to base64. The JavaScript action content should look like: // Get variable value from VariableManager var PreEncVar = context.variableManager.getValue("pre_encode"); if (PreEncVar==null) { context.fail("Variable 'PreEncVar' not found"); } // Log the pre-Encoded value for reference logger.debug("PreComputedValue = "+PreEncVar); // Do some computation using the methods // you defined in the JS Library. This case the Base64 JS function // Then, log the value to show what it is after encoding var EncodedValue = Base64.encode(PreEncVar); logger.debug("PostComputedValue = "+EncodedValue); // Export the computed value in a runtime variable back to Neoload to use context.variableManager.setValue("Base64Var",EncodedValue); Then you can use the variable ${Base64Var} in your requests.