diff --git a/libstats/include/stats_event.h b/libstats/include/stats_event.h
index 504d0890f..2811f52f4 100644
--- a/libstats/include/stats_event.h
+++ b/libstats/include/stats_event.h
@@ -53,11 +53,13 @@ struct stats_event;
 #define ERROR_NO_ATOM_ID 0x2
 #define ERROR_OVERFLOW 0x4
 #define ERROR_ATTRIBUTION_CHAIN_TOO_LONG 0x8
-#define ERROR_ANNOTATION_DOES_NOT_FOLLOW_FIELD 0x10
-#define ERROR_INVALID_ANNOTATION_ID 0x20
-#define ERROR_ANNOTATION_ID_TOO_LARGE 0x40
-#define ERROR_TOO_MANY_ANNOTATIONS 0x80
-#define ERROR_TOO_MANY_FIELDS 0x100
+#define ERROR_TOO_MANY_KEY_VALUE_PAIRS 0x10
+#define ERROR_ANNOTATION_DOES_NOT_FOLLOW_FIELD 0x20
+#define ERROR_INVALID_ANNOTATION_ID 0x40
+#define ERROR_ANNOTATION_ID_TOO_LARGE 0x80
+#define ERROR_TOO_MANY_ANNOTATIONS 0x100
+#define ERROR_TOO_MANY_FIELDS 0x200
+#define ERROR_INVALID_VALUE_TYPE 0x400
 
 /* TYPE IDS */
 #define INT32_TYPE 0x00
@@ -88,6 +90,30 @@ void stats_event_write_string8(struct stats_event* event, char* buf, uint32_t nu
 void stats_event_write_attribution_chain(struct stats_event* event, uint32_t* uids, char** tags,
                                          uint32_t* tagLengths, uint32_t numNodes);
 
+/* key_value_pair struct can be constructed as follows:
+ *    struct key_value_pair pair;
+ *    pair.key = key;
+ *    pair.typeId = STRING_TYPE;
+ *    pair.stringValue = buf;
+ *    pair.stringBytes = strlen(buf);
+ */
+struct key_value_pair {
+    int32_t key;
+    uint8_t valueType;  // expected to be INT32_TYPE, INT64_TYPE, FLOAT_TYPE, or STRING_TYPE
+    union {
+        int32_t int32Value;
+        int64_t int64Value;
+        float floatValue;
+        struct {
+            char* stringValue;
+            uint32_t stringBytes;
+        };
+    };
+};
+
+void stats_event_add_key_value_pairs(struct stats_event* event, struct key_value_pair* pairs,
+                                     uint32_t numPairs);
+
 void stats_event_add_bool_annotation(struct stats_event* event, uint32_t annotationId, bool value);
 void stats_event_add_int32_annotation(struct stats_event* event, uint32_t annotationId,
                                       int32_t value);
diff --git a/libstats/stats_event.c b/libstats/stats_event.c
index 58558b3ba..5e41d72a6 100644
--- a/libstats/stats_event.c
+++ b/libstats/stats_event.c
@@ -36,9 +36,7 @@
 
 /* LIMITS */
 #define MAX_ANNOTATION_COUNT 15
-#define MAX_ANNOTATION_ID 127
-#define MAX_ATTRIBUTION_NODES 127
-#define MAX_NUM_ELEMENTS 127
+#define MAX_BYTE_VALUE 127  // parsing side requires that lengths fit in 7 bits
 
 // The stats_event struct holds the serialized encoding of an event
 // within a buf. Also includes other required fields.
@@ -46,6 +44,7 @@ struct stats_event {
     byte buf[MAX_EVENT_PAYLOAD];
     size_t bufPos;        // current write position within the buf
     size_t lastFieldPos;  // location of last field within the buf
+    byte lastFieldType;   // type of last field
     size_t size;          // number of valid bytes within buffer
     uint32_t numElements;
     uint32_t atomId;
@@ -69,6 +68,7 @@ struct stats_event* stats_event_obtain() {
 
     event->bufPos = POS_FIRST_FIELD;
     event->lastFieldPos = 0;
+    event->lastFieldType = OBJECT_TYPE;
     event->size = 0;
     event->numElements = 0;
     event->atomId = 0;
@@ -144,81 +144,69 @@ static size_t put_byte_array(struct stats_event* event, void* buf, size_t size)
     return 0;
 }
 
+static void start_field(struct stats_event* event, byte typeId) {
+    event->lastFieldPos = event->bufPos;
+    event->lastFieldType = typeId;
+    event->bufPos += put_byte(event, typeId);
+    event->numElements++;
+}
+
 void stats_event_write_int32(struct stats_event* event, int32_t value) {
     if (!event || event->errors) return;
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, INT32_TYPE);
+    start_field(event, INT32_TYPE);
     event->bufPos += put_int32(event, value);
-    event->numElements++;
 }
 
 void stats_event_write_int64(struct stats_event* event, int64_t value) {
     if (!event || event->errors) return;
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, INT64_TYPE);
+    start_field(event, INT64_TYPE);
     event->bufPos += put_int64(event, value);
-    event->numElements++;
 }
 
 void stats_event_write_float(struct stats_event* event, float value) {
     if (!event || event->errors) return;
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, FLOAT_TYPE);
+    start_field(event, FLOAT_TYPE);
     event->bufPos += put_float(event, value);
-    event->numElements++;
 }
 
 void stats_event_write_bool(struct stats_event* event, bool value) {
     if (!event || event->errors) return;
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, BOOL_TYPE);
+    start_field(event, BOOL_TYPE);
     event->bufPos += put_bool(event, value);
-    event->numElements++;
 }
 
 // Buf is assumed to be encoded using UTF8
 void stats_event_write_byte_array(struct stats_event* event, uint8_t* buf, uint32_t numBytes) {
     if (!event || !buf || event->errors) return;
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, BYTE_ARRAY_TYPE);
+    start_field(event, BYTE_ARRAY_TYPE);
     event->bufPos += put_int32(event, numBytes);
     event->bufPos += put_byte_array(event, buf, numBytes);
-    event->numElements++;
 }
 
 // Buf is assumed to be encoded using UTF8
 void stats_event_write_string8(struct stats_event* event, char* buf, uint32_t numBytes) {
     if (!event || !buf || event->errors) return;
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, STRING_TYPE);
+    start_field(event, STRING_TYPE);
     event->bufPos += put_int32(event, numBytes);
     event->bufPos += put_byte_array(event, buf, numBytes);
-    event->numElements++;
-}
-
-// Side-effect: modifies event->errors if the attribution chain is too long
-static bool is_attribution_chain_too_long(struct stats_event* event, uint32_t numNodes) {
-    if (numNodes > MAX_ATTRIBUTION_NODES) {
-        event->errors |= ERROR_ATTRIBUTION_CHAIN_TOO_LONG;
-        return true;
-    }
-    return false;
 }
 
 // Tags are assumed to be encoded using UTF8
 void stats_event_write_attribution_chain(struct stats_event* event, uint32_t* uids, char** tags,
                                          uint32_t* tagLengths, uint32_t numNodes) {
     if (!event || event->errors) return;
-    if (is_attribution_chain_too_long(event, numNodes)) return;
+    if (numNodes > MAX_BYTE_VALUE) {
+        event->errors |= ERROR_ATTRIBUTION_CHAIN_TOO_LONG;
+        return;
+    }
 
-    event->lastFieldPos = event->bufPos;
-    event->bufPos += put_byte(event, ATTRIBUTION_CHAIN_TYPE);
+    start_field(event, ATTRIBUTION_CHAIN_TYPE);
     event->bufPos += put_byte(event, (byte)numNodes);
 
     for (int i = 0; i < numNodes; i++) {
@@ -226,7 +214,41 @@ void stats_event_write_attribution_chain(struct stats_event* event, uint32_t* ui
         event->bufPos += put_int32(event, tagLengths[i]);
         event->bufPos += put_byte_array(event, tags[i], tagLengths[i]);
     }
-    event->numElements++;
+}
+
+void stats_event_add_key_value_pairs(struct stats_event* event, struct key_value_pair* pairs,
+                                     uint32_t numPairs) {
+    if (!event || event->errors) return;
+    if (numPairs > MAX_BYTE_VALUE) {
+        event->errors |= ERROR_TOO_MANY_KEY_VALUE_PAIRS;
+        return;
+    }
+
+    start_field(event, KEY_VALUE_PAIRS_TYPE);
+    event->bufPos += put_byte(event, (byte)numPairs);
+
+    for (int i = 0; i < numPairs; i++) {
+        event->bufPos += put_int32(event, pairs[i].key);
+        event->bufPos += put_byte(event, pairs[i].valueType);
+        switch (pairs[i].valueType) {
+            case INT32_TYPE:
+                event->bufPos += put_int32(event, pairs[i].int32Value);
+                break;
+            case INT64_TYPE:
+                event->bufPos += put_int64(event, pairs[i].int64Value);
+                break;
+            case FLOAT_TYPE:
+                event->bufPos += put_float(event, pairs[i].floatValue);
+                break;
+            case STRING_TYPE:
+                event->bufPos += put_int32(event, pairs[i].stringBytes);
+                event->bufPos += put_byte_array(event, pairs[i].stringValue, pairs[i].stringBytes);
+                break;
+            default:
+                event->errors |= ERROR_INVALID_VALUE_TYPE;
+                return;
+        }
+    }
 }
 
 // Side-effect: modifies event->errors if annotation does not follow field
@@ -240,7 +262,7 @@ static bool does_annotation_follow_field(struct stats_event* event) {
 
 // Side-effect: modifies event->errors if annotation id is too large
 static bool is_valid_annotation_id(struct stats_event* event, uint32_t annotationId) {
-    if (annotationId > MAX_ANNOTATION_ID) {
+    if (annotationId > MAX_BYTE_VALUE) {
         event->errors |= ERROR_ANNOTATION_ID_TOO_LARGE;
         return false;
     }
@@ -250,15 +272,15 @@ static bool is_valid_annotation_id(struct stats_event* event, uint32_t annotatio
 // Side-effect: modifies event->errors if field has too many annotations
 static void increment_annotation_count(struct stats_event* event) {
     byte fieldType = event->buf[event->lastFieldPos] & 0x0F;
-    byte oldAnnotationCount = event->buf[event->lastFieldPos] & 0xF0;
-    byte newAnnotationCount = oldAnnotationCount + 1;
+    uint32_t oldAnnotationCount = event->buf[event->lastFieldPos] & 0xF0;
+    uint32_t newAnnotationCount = oldAnnotationCount + 1;
 
     if (newAnnotationCount > MAX_ANNOTATION_COUNT) {
         event->errors |= ERROR_TOO_MANY_ANNOTATIONS;
         return;
     }
 
-    event->buf[event->lastFieldPos] = ((newAnnotationCount << 4) & 0xF0) | fieldType;
+    event->buf[event->lastFieldPos] = (((byte)newAnnotationCount << 4) & 0xF0) | fieldType;
 }
 
 void stats_event_add_bool_annotation(struct stats_event* event, uint32_t annotationId, bool value) {
@@ -292,13 +314,6 @@ static void build(struct stats_event* event) {
     // store size before we modify bufPos
     event->size = event->bufPos;
 
-    if (event->numElements > MAX_NUM_ELEMENTS) {
-        event->errors |= ERROR_TOO_MANY_FIELDS;
-    } else {
-        event->bufPos = POS_NUM_ELEMENTS;
-        put_byte(event, (byte)event->numElements);
-    }
-
     if (event->timestampNs == 0) {
         event->errors |= ERROR_NO_TIMESTAMP;
     } else {
@@ -308,6 +323,7 @@ static void build(struct stats_event* event) {
         event->bufPos = POS_TIMESTAMP;
         event->bufPos += put_byte(event, INT64_TYPE);
         event->bufPos += put_int64(event, event->timestampNs);
+        event->numElements++;
     }
 
     if (event->atomId == 0) {
@@ -316,6 +332,14 @@ static void build(struct stats_event* event) {
         event->bufPos = POS_ATOM_ID;
         event->bufPos += put_byte(event, INT32_TYPE);
         event->bufPos += put_int64(event, event->atomId);
+        event->numElements++;
+    }
+
+    if (event->numElements > MAX_BYTE_VALUE) {
+        event->errors |= ERROR_TOO_MANY_FIELDS;
+    } else {
+        event->bufPos = POS_NUM_ELEMENTS;
+        put_byte(event, (byte)event->numElements);
     }
 
     // If there are errors, rewrite buffer