diff --git a/.gitignore b/.gitignore
index 6666f22..3698040 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 .eunit
 deps
 erln8.config
+jiffy.plt
diff --git a/Makefile b/Makefile
index 025486e..eb28390 100644
--- a/Makefile
+++ b/Makefile
@@ -29,15 +29,38 @@ build: depends
 	$(REBAR) compile
 
 
-eunit:
+eunit: build
 	$(REBAR) eunit skip_deps=true
 
 
-check: build eunit
+check: build eunit dialyzer
 
 
 %.beam: %.erl
 	erlc -o test/ $<
 
+DIALYZER = dialyzer
+DIALYZER_OPTS ?=
+JIFFY_PLT = jiffy.plt
+ERLANG_DIALYZER_APPS ?= asn1 \
+                        compiler \
+                        crypto \
+                        edoc \
+                        erts \
+                        inets \
+                        kernel \
+                        mnesia \
+                        public_key \
+                        ssl \
+                        stdlib \
+                        syntax_tools \
+                        tools \
+                        xmerl
+$(JIFFY_PLT):
+	@echo "Missing $(JIFFY_PLT). Please wait while a new PLT is compiled."
+	$(DIALYZER) --build_plt --apps $(ERLANG_DIALYZER_APPS) --output_plt $(JIFFY_PLT)
+
+dialyzer: $(JIFFY_PLT) build
+	@$(DIALYZER) $(DIALYZER_OPTS) --plts $(JIFFY_PLT) -r ebin
 
 .PHONY: all clean distclean depends build etap eunit check
diff --git a/src/jiffy.erl b/src/jiffy.erl
index 23a0c9d..7bd0206 100644
--- a/src/jiffy.erl
+++ b/src/jiffy.erl
@@ -5,13 +5,41 @@
 -export([decode/1, decode/2, encode/1, encode/2]).
 -define(NOT_LOADED, not_loaded(?LINE)).
 
--on_load(init/0).
 
+%% More information on the JSON standard: http://json.org
+-type json_value() :: null
+                    | true
+                    | false
+                    | json_string()
+                    | json_number()
+                    | json_object()
+                    | json_array().
+
+
+-type json_array()  :: [json_value()].
+-type json_string() :: binary().
+-type json_number() :: integer() | float().
+-type json_object() :: {[{json_string(),json_value()}]}.
+
+-type decode_option() :: return_maps
+                       | {bytes_per_iter, non_neg_integer()}.
+-type decode_options() :: [decode_option()].
+
+-type encode_option() :: unescape
+                       | pretty
+                       | force_utf8
+                       | {bytes_per_iter, non_neg_integer()}.
+-type encode_options() :: [encode_option()].
+
+-export_type([json_value/0]).
 
+-on_load(init/0).
+
+-spec decode(iolist() | binary()) -> json_value().
 decode(Data) ->
     decode(Data, []).
 
-
+-spec decode(iolist() | binary(), decode_options()) -> json_value().
 decode(Data, Opts) when is_binary(Data), is_list(Opts) ->
     case nif_decode_init(Data, Opts) of
         {error, _} = Error ->
@@ -26,11 +54,11 @@ decode(Data, Opts) when is_binary(Data), is_list(Opts) ->
 decode(Data, Opts) when is_list(Data) ->
     decode(iolist_to_binary(Data), Opts).
 
-
+-spec encode(json_value()) -> iolist().
 encode(Data) ->
     encode(Data, []).
 
-
+-spec encode(json_value(), encode_options()) -> iolist().
 encode(Data, Options) ->
     ForceUTF8 = lists:member(force_utf8, Options),
     case nif_encode_init(Data, Options) of