diff --git a/src/landmarks/data.ml b/src/landmarks/data.ml
index a8372fc..4738148 100644
--- a/src/landmarks/data.ml
+++ b/src/landmarks/data.ml
@@ -8,12 +8,12 @@ type gc_info = {
 (** Basic GC statistics *)
 
 (** Convert gc_info to yojson *)
-let gc_info_to_yojson (gc : gc_info) : Yojson.Safe.t =
+let gc_info_to_yojson (self : gc_info) : Yojson.Safe.t =
   `Assoc
     [
-      "minor_words", `Float gc.minor_words;
-      "promoted_words", `Float gc.promoted_words;
-      "major_words", `Float gc.major_words;
+      "minor_words", `Float self.minor_words;
+      "promoted_words", `Float self.promoted_words;
+      "major_words", `Float self.major_words;
     ]
 
 type timing = {
@@ -25,13 +25,13 @@ type timing = {
 (** Timing information *)
 
 (** Convert timing to yojson *)
-let timing_to_yojson (t : timing) : Yojson.Safe.t =
+let timing_to_yojson (self : timing) : Yojson.Safe.t =
   `Assoc
     [
-      "start_time", `Float t.start_time;
-      "end_time", `Float t.end_time;
-      "duration", `Float t.duration;
-      "cpu_time", `Float t.cpu_time;
+      "start_time", `Float self.start_time;
+      "end_time", `Float self.end_time;
+      "duration", `Float self.duration;
+      "cpu_time", `Float self.cpu_time;
     ]
 
 type landmark = {
@@ -45,17 +45,17 @@ type landmark = {
 (** A single landmark measurement *)
 
 (** Convert landmark to yojson *)
-let landmark_to_yojson (lm : landmark) : Yojson.Safe.t =
+let landmark_to_yojson (self : landmark) : Yojson.Safe.t =
   `Assoc
     ([
-       "name", `String lm.name;
-       "timing", timing_to_yojson lm.timing;
-       "gc_before", gc_info_to_yojson lm.gc_before;
-       "gc_after", gc_info_to_yojson lm.gc_after;
-       "call_count", `Int lm.call_count;
+       "name", `String self.name;
+       "timing", timing_to_yojson self.timing;
+       "gc_before", gc_info_to_yojson self.gc_before;
+       "gc_after", gc_info_to_yojson self.gc_after;
+       "call_count", `Int self.call_count;
      ]
     @
-    match lm.location with
+    match self.location with
     | None -> []
     | Some loc -> [ "location", `String loc ])
 
diff --git a/src/landmarks/data.mli b/src/landmarks/data.mli
new file mode 100644
index 0000000..1a98380
--- /dev/null
+++ b/src/landmarks/data.mli
@@ -0,0 +1,52 @@
+(** Basic data types for Landmarks profiling export *)
+
+(** GC statistics at a point in time *)
+type gc_info = {
+  minor_words : float;
+  promoted_words : float;
+  major_words : float;
+  minor_collections : int;
+  major_collections : int;
+  heap_words : int;
+  compactions : int;
+}
+
+val gc_info_to_yojson : gc_info -> Yojson.Safe.t
+(** Convert gc_info to yojson *)
+
+(** Timing information *)
+type timing = {
+  start_time : float;  (** Start timestamp (seconds) *)
+  end_time : float;    (** End timestamp (seconds) *)
+  duration : float;    (** Duration in seconds *)
+  cpu_time : float;    (** CPU time in seconds *)
+}
+
+val timing_to_yojson : timing -> Yojson.Safe.t
+(** Convert timing to yojson *)
+
+(** A single landmark measurement *)
+type landmark = {
+  name : string;
+  location : string option;
+  timing : timing;
+  gc_before : gc_info;
+  gc_after : gc_info;
+  call_count : int;
+}
+
+val landmark_to_yojson : landmark -> Yojson.Safe.t
+(** Convert landmark to yojson *)
+
+(** A collection of landmarks *)
+type landmark_collection = {
+  landmarks : landmark list;
+  total_time : float;
+  timestamp : float;
+}
+
+val landmark_collection_to_yojson : landmark_collection -> Yojson.Safe.t
+(** Convert landmark_collection to yojson *)
+
+val get_gc_info : unit -> gc_info
+(** Helper to get current GC info from Gc.stat *)