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dictionaries/README.md
+# AFL dictionaries
+
+(See [../docs/README.md](../docs/README.md) for the general instruction manual.)
+
+This subdirectory contains a set of dictionaries that can be used in
+conjunction with the -x option to allow the fuzzer to effortlessly explore the
+grammar of some of the more verbose data formats or languages. The basic
+principle behind the operation of fuzzer dictionaries is outlined in section 10
+of the "main" README.md for the project.
+
+Custom dictionaries can be added at will. They should consist of a
+reasonably-sized set of rudimentary syntax units that the fuzzer will then try
+to clobber together in various ways. Snippets between 2 and 16 bytes are
+usually the sweet spot.
+
+Custom dictionaries can be created in two ways:
+
+ - By creating a new directory and placing each token in a separate file, in
+ which case, there is no need to escape or otherwise format the data.
+
+ - By creating a flat text file where tokens are listed one per line in the
+ format of name="value". The alphanumeric name is ignored and can be omitted,
+ although it is a convenient way to document the meaning of a particular
+ token. The value must appear in quotes, with hex escaping (\xNN) applied to
+ all non-printable, high-bit, or otherwise problematic characters (\\ and \"
+ shorthands are recognized, too).
+
+The fuzzer auto-selects the appropriate mode depending on whether the -x
+parameter is a file or a directory.
+
+In the file mode, every name field can be optionally followed by @<num>, e.g.:
+
+ `keyword_foo@1 = "foo"`
+
+Such entries will be loaded only if the requested dictionary level is equal or
+higher than this number. The default level is zero; a higher value can be set
+by appending @<num> to the dictionary file name, like so:
+
+ `-x path/to/dictionary.dct@2`
+
+Good examples of dictionaries can be found in xml.dict and png.dict.

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