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+Fuzz Tests for CPython
+======================
+
+These fuzz tests are designed to be included in Google's `oss-fuzz`_ project.
+
+oss-fuzz works against a library exposing a function of the form
+``int LLVMFuzzerTestOneInput(const uint8_t* data, size_t length)``. We provide
+that library (``fuzzer.c``), and include a ``_fuzz`` module for testing with
+some toy values -- no fuzzing occurs in Python's test suite.
+
+oss-fuzz will regularly pull from CPython, discover all the tests in
+``fuzz_tests.txt``, and run them -- so adding a new test here means it will
+automatically be run in oss-fuzz, while also being smoke-tested as part of
+CPython's test suite.
+
+Adding a new fuzz test
+----------------------
+
+Add the test name on a new line in ``fuzz_tests.txt``.
+
+In ``fuzzer.c``, add a function to be run::
+
+    int $test_name (const char* data, size_t size) {
+        ...
+        return 0;
+    }
+
+
+And invoke it from ``LLVMFuzzerTestOneInput``::
+
+    #if _Py_FUZZ_YES(fuzz_builtin_float)
+        rv |= _run_fuzz(data, size, fuzz_builtin_float);
+    #endif
+
+``LLVMFuzzerTestOneInput`` will run in oss-fuzz, with each test in
+``fuzz_tests.txt`` run separately.
+
+What makes a good fuzz test
+---------------------------
+
+Libraries written in C that might handle untrusted data are worthwhile. The
+more complex the logic (e.g. parsing), the more likely this is to be a useful
+fuzz test. See the existing examples for reference, and refer to the
+`oss-fuzz`_ docs.
+
+.. _oss-fuzz: https://github.com/google/oss-fuzz