For an AES encryption tool, first identify the mode and how it packages the IV or nonce, ciphertext, and authentication tag. Run the same disposable plaintext twice. In a correctly configured randomized or nonce-based workflow, the stored output should contain what is needed for decryption without reusing an IV under the same key.
Verify the output with an independent implementation and test that changing one ciphertext byte causes authenticated decryption to fail. Keep real secrets out of a browser tool until its data handling is understood. A useful report includes mode, input encoding, exported format, and a non-sensitive test vector. The Web Crypto AES-GCM parameters explain why IV uniqueness matters.
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