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+# Choosing initial test cases
+
+To operate correctly, the fuzzer requires one or more starting file that
+contains a good example of the input data normally expected by the targeted
+application. There are two basic rules:
+
+  - Keep the files small. Under 1 kB is ideal, although not strictly necessary.
+    For a discussion of why size matters, see [perf_tips.md](perf_tips.md).
+
+  - Use multiple test cases only if they are functionally different from
+    each other. There is no point in using fifty different vacation photos
+    to fuzz an image library.
+
+You can find many good examples of starting files in the testcases/ subdirectory
+that comes with this tool.
+
+PS. If a large corpus of data is available for screening, you may want to use
+the afl-cmin utility to identify a subset of functionally distinct files that
+exercise different code paths in the target binary.
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