XSS Payload Encoder

Test your own application for cross-site scripting encoding bypasses

Testing whether your own application is vulnerable to cross-site scripting encoding bypasses is part of securing it, and doing so requires understanding the vulnerability class. This tool helps you generate test cases for cross-site scripting encoding bypasses so you can check your own application, under authorisation, and confirm that your defences hold. It encodes test strings in the various ways an attacker might, so you can verify your output encoding defends against each rather than only the obvious form.

Why this vulnerability matters

XSS defences can be bypassed if input is encoded in a form the filter does not recognise but the browser still executes, so testing against multiple encodings matters. An incomplete encoding defence gives false confidence. It appears in the OWASP Top Ten precisely because it is common and serious, which is why testing for it against your own applications, and understanding how it works, is essential to defending against it.

The defence, and responsible use

The defence is contextual output encoding that handles all the forms input can take, plus a Content Security Policy. Testing against encoded variants confirms the defence is not bypassable by a simple transformation. This tool is for authorised security testing of systems you own or have explicit permission to test, for security research, and for education, testing without authorisation is illegal and unethical. It runs entirely in your browser, so nothing you enter is uploaded.

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