diff --git a/src/storage/mappingPreimages.js b/src/storage/mappingPreimages.js
index b85901e8ef..5156f0191a 100644
--- a/src/storage/mappingPreimages.js
+++ b/src/storage/mappingPreimages.js
@@ -4,6 +4,13 @@ module.exports = {
   extractMappingPreimages: extractMappingPreimages
 }
 
+/**
+ * Uses the storageViewer to retrieve the storage and returns a mapping containing possible solidity mappping type location.
+ * like { "<mapping_slot>" : { "<mapping-key1>": preimageOf1 }, { "<mapping-key2>": preimageOf2 }, ... }
+ *
+ * @param {Object} address  - storageViewer
+ * @return {Map} - solidity mapping location
+ */
 async function extractMappingPreimages (storageViewer) {
   return new Promise((resolve, reject) => {
     storageViewer.storageRange(function (error, storage) {
@@ -22,6 +29,14 @@ async function extractMappingPreimages (storageViewer) {
   })
 }
 
+/**
+ * Uses the storageViewer to retrieve the storage and returns a mapping containing possible solidity mappping type location.
+ * like { "<mapping_slot>" : { "<mapping-key1>": preimageOf1 }, { "<mapping-key2>": preimageOf2 }, ... }
+ *
+ * @param {Object} storage  - storage given by storage Viewer (basically a mapping hashedkey : {key, value})
+ * @param {Function} callback  - calback
+ * @return {Map} - solidity mapping location (e.g { "<mapping_slot>" : { "<mapping-key1>": preimageOf1 }, { "<mapping-key2>": preimageOf2 }, ... })
+ */
 async function decodeMappingsKeys (storage, callback) {
   var ret = {}
   for (var hashedLoc in storage) {
@@ -45,6 +60,12 @@ async function decodeMappingsKeys (storage, callback) {
   callback(null, ret)
 }
 
+/**
+ * Uses web3 to return preimage of a key
+ *
+ * @param {String} key  - key to retrieve the preimage of
+ * @return {String} - preimage of the given key
+ */
 function getPreimage (key) {
   return new Promise((resolve, reject) => {
     global.web3.debug.preimage(key, function (error, preimage) {