diff --git a/src/exometer_prometheus_fmt.erl b/src/exometer_prometheus_fmt.erl
new file mode 100644
index 0000000..b0a15a4
--- /dev/null
+++ b/src/exometer_prometheus_fmt.erl
@@ -0,0 +1,103 @@
+-module(exometer_prometheus_fmt).
+
+-export([
+    name/1,
+    type/1,
+    metrics/1
+]).
+
+-type prom_name()       :: iolist().
+-type prom_type()       :: iolist().
+-type prom_help()       :: iolist().
+-type prom_text()       :: binary().
+-type metric_info()     :: {exometer:name(),
+                            exometer:value(),
+                            prom_name(),
+                            prom_type(),
+                            prom_help()}.
+
+
+%% -------------------------------------------------------
+%% Public API
+%% -------------------------------------------------------
+
+-spec name(exometer:name()) -> binary().
+name(MetricId) ->
+    NameList = lists:join($_, lists:map(fun ioize/1, MetricId)),
+    NameBin = iolist_to_binary(NameList),
+    re:replace(NameBin, "-|\\.", "_", [global, {return,binary}]).
+
+-spec type(atom()) -> binary().
+type(undefined)     -> <<"untyped">>;
+type(counter)       -> <<"gauge">>;
+type(gauge)         -> <<"gauge">>;
+type(spiral)        -> <<"gauge">>;
+type(histogram)     -> <<"summary">>;
+type(function)      -> <<"gauge">>;
+type(Tuple) when is_tuple(Tuple) ->
+    case element(1, Tuple) of
+        function -> <<"gauge">>;
+        _Else    -> <<"untyped">>
+    end.
+
+-spec metrics([metric_info()]) -> prom_text().
+metrics(Metrics) ->
+    Formatted = metrics(Metrics, []),
+    iolist_to_binary(Formatted).
+
+
+%% -------------------------------------------------------
+%% Internal
+%% -------------------------------------------------------
+
+metrics([], Akk) ->
+    Akk;
+metrics([{Metric, DataPoints, Name, Type, Help} | Metrics], Akk) ->
+    Payload = [[<<"# HELP ">>, Name, <<" ">>, Help, <<"\n">>,
+                <<"# TYPE ">>, Name, <<" ">>, Type, <<"\n">>] |
+               [[Name, map_datapoint(DPName), <<" ">>, ioize(Value), <<"\n">>]
+               || {DPName, Value} <- DataPoints, is_valid_datapoint(DPName)]],
+    Payload1 = maybe_add_sum(Payload, Name, Metric, Type),
+    metrics(Metrics, [Payload1, <<"\n">> | Akk]).
+
+ioize(Atom) when is_atom(Atom) ->
+    atom_to_binary(Atom, utf8);
+ioize(Number) when is_float(Number) ->
+    float_to_binary(Number, [{decimals, 4}]);
+ioize(Number) when is_integer(Number) ->
+    integer_to_binary(Number);
+ioize(Something) ->
+    Something.
+
+maybe_add_sum(Payload, MetricName, Metric, <<"summary">>) ->
+    {ok, [{mean, Mean}, {n, N}]} = exometer:get_value(Metric, [mean, n]),
+    [Payload | [MetricName, <<"_sum ">>, ioize(Mean * N), <<"\n">>]];
+maybe_add_sum(Payload, _MetricName, _Metric, _Else) ->
+    Payload.
+
+map_datapoint(value)    -> <<"">>;
+map_datapoint(one)      -> <<"">>;
+map_datapoint(n)        -> <<"_count">>;
+map_datapoint(50)       -> <<"{quantile=\"0.5\"}">>;
+map_datapoint(90)       -> <<"{quantile=\"0.9\"}">>;
+map_datapoint(Integer) when is_integer(Integer)  ->
+    Bin = ioize(Integer),
+    <<"{quantile=\"0.", Bin/binary, "\"}">>;
+map_datapoint(Something)  ->
+    %% this is for functions with alternative datapoints
+    Bin = ioize(Something),
+    <<"{datapoint=\"", Bin/binary, "\"}">>.
+
+is_valid_datapoint(value) -> true;
+is_valid_datapoint(one) -> true;
+is_valid_datapoint(n) -> true;
+is_valid_datapoint(Number) when is_number(Number) -> true;
+is_valid_datapoint(count) -> false;
+is_valid_datapoint(mean) -> false;
+is_valid_datapoint(min) -> false;
+is_valid_datapoint(max) -> false;
+is_valid_datapoint(median) -> false;
+is_valid_datapoint(ms_since_reset) -> false;
+%% this is for functions with alternative datapoints
+is_valid_datapoint(_Else) -> true.
+
diff --git a/src/exometer_report_prometheus.erl b/src/exometer_report_prometheus.erl
index a4728fb..c89c768 100644
--- a/src/exometer_report_prometheus.erl
+++ b/src/exometer_report_prometheus.erl
@@ -24,6 +24,7 @@
 %% Public API
 %% -------------------------------------------------------
 
+-spec fetch() -> exometer_prometheus_fmt:prom_text().
 fetch() ->
     exometer_report:call_reporter(exometer_report_prometheus, {request, fetch}).
 
@@ -40,11 +41,11 @@ exometer_init(Opts) ->
     {ok, #state{}}.
 
 exometer_subscribe(Metric, DataPoints, _Interval, Opts, State = #state{entries=Entries}) ->
-    Name = make_metric_name(Metric),
+    Name = exometer_prometheus_fmt:name(Metric),
     Help = proplists:get_value(help, Opts, <<"undefined">>),
     Type = case proplists:get_value(type, Opts, undefined) of
-               undefined -> map_type(exometer:info(Metric, type));
-               SomeType  -> ioize(SomeType)
+               undefined -> exometer_prometheus_fmt:type(exometer:info(Metric, type));
+               SomeType  -> atom_to_binary(SomeType, latin1)
            end,
     Entry = {Metric, DataPoints, Name, Type, Help},
     {ok, State#state{entries = Entries ++ [Entry]}}.
@@ -71,7 +72,7 @@ exometer_terminate(_Reason, _) -> ignore.
 
 fetch_and_format_metrics(Entries) ->
     Metrics = fetch_metrics(Entries),
-    format_metrics(Metrics).
+    exometer_prometheus_fmt:metrics(Metrics).
 
 fetch_metrics(Entries) ->
     fetch_metrics(Entries, []).
@@ -86,75 +87,3 @@ fetch_metrics([{Metric, DataPoints, Name, Type, Help} | Entries], Akk) ->
             fetch_metrics(Entries, Akk)
     end.
 
-format_metrics(Metrics) ->
-    Formatted = format_metrics(Metrics, []),
-    iolist_to_binary(Formatted).
-
-format_metrics([], Akk) ->
-    Akk;
-format_metrics([{Metric, DataPoints, Name, Type, Help} | Metrics], Akk) ->
-    Payload = [[<<"# HELP ">>, Name, <<" ">>, Help, <<"\n">>,
-                <<"# TYPE ">>, Name, <<" ">>, Type, <<"\n">>] |
-               [[Name, map_datapoint(DPName), <<" ">>, ioize(Value), <<"\n">>]
-               || {DPName, Value} <- DataPoints, is_valid_datapoint(DPName)]],
-    Payload1 = maybe_add_sum(Payload, Name, Metric, Type),
-    format_metrics(Metrics, [Payload1, <<"\n">> | Akk]).
-
-make_metric_name(Metric) ->
-    NameList = lists:join($_, lists:map(fun ioize/1, Metric)),
-    NameBin = iolist_to_binary(NameList),
-    re:replace(NameBin, "-|\\.", "_", [global, {return,binary}]).
-
-ioize(Atom) when is_atom(Atom) ->
-    atom_to_binary(Atom, utf8);
-ioize(Number) when is_float(Number) ->
-    float_to_binary(Number, [{decimals, 4}]);
-ioize(Number) when is_integer(Number) ->
-    integer_to_binary(Number);
-ioize(Something) ->
-    Something.
-
-maybe_add_sum(Payload, MetricName, Metric, <<"summary">>) ->
-    {ok, [{mean, Mean}, {n, N}]} = exometer:get_value(Metric, [mean, n]),
-    [Payload | [MetricName, <<"_sum ">>, ioize(Mean * N), <<"\n">>]];
-maybe_add_sum(Payload, _MetricName, _Metric, _Else) ->
-    Payload.
-
-map_type(undefined)     -> <<"untyped">>;
-map_type(counter)       -> <<"gauge">>;
-map_type(gauge)         -> <<"gauge">>;
-map_type(spiral)        -> <<"gauge">>;
-map_type(histogram)     -> <<"summary">>;
-map_type(function)      -> <<"gauge">>;
-map_type(Tuple) when is_tuple(Tuple) ->
-    case element(1, Tuple) of
-        function -> <<"gauge">>;
-        _Else    -> <<"untyped">>
-    end.
-
-map_datapoint(value)    -> <<"">>;
-map_datapoint(one)      -> <<"">>;
-map_datapoint(n)        -> <<"_count">>;
-map_datapoint(50)       -> <<"{quantile=\"0.5\"}">>;
-map_datapoint(90)       -> <<"{quantile=\"0.9\"}">>;
-map_datapoint(Integer) when is_integer(Integer)  ->
-    Bin = ioize(Integer),
-    <<"{quantile=\"0.", Bin/binary, "\"}">>;
-map_datapoint(Something)  ->
-    %% this is for functions with alternative datapoints
-    Bin = ioize(Something),
-    <<"{datapoint=\"", Bin/binary, "\"}">>.
-
-is_valid_datapoint(value) -> true;
-is_valid_datapoint(one) -> true;
-is_valid_datapoint(n) -> true;
-is_valid_datapoint(Number) when is_number(Number) -> true;
-is_valid_datapoint(count) -> false;
-is_valid_datapoint(mean) -> false;
-is_valid_datapoint(min) -> false;
-is_valid_datapoint(max) -> false;
-is_valid_datapoint(median) -> false;
-is_valid_datapoint(ms_since_reset) -> false;
-%% this is for functions with alternative datapoints
-is_valid_datapoint(_Else) -> true.
-