diff --git a/functions.cpp b/functions.cpp
index 2007dca..f7db7b8 100644
--- a/functions.cpp
+++ b/functions.cpp
@@ -34,7 +34,7 @@ std::vector< RenameLibrary > getLibraries(const std::vector<std::pair<std::strin
             result.push_back( rl );
             goto dlsymerror;
         }
-        rl.getCustomKeys = ( std::vector< std::string >( * )() )dlsym(
+        rl.getCustomKeys = ( std::vector< std::pair< std::string, std::string > >( * )() )dlsym(
             libhndl, "getCustomKeys" );
         if ( !rl.getCustomKeys ) {
             result.push_back( rl );
diff --git a/library.hpp b/library.hpp
index d9f2805..9774a2c 100644
--- a/library.hpp
+++ b/library.hpp
@@ -15,11 +15,17 @@ using string = std::string;
 
 #endif
 
+#define STRING_TYPE "string"
+#define NUM_TYPE "number"
+#define YEAR_TYPE "year"
+#define DATE_TYPE "date"
+#define BOOL_TYPE "bool"
+
 extern "C" {
 bool init(const string &configuration);
 std::vector< RenameObject > getOptions( const RenameObject &search );
 bool renamePath( const string &path, const RenameObject &renamer );
-std::vector< string > getCustomKeys();
+std::vector< std::pair<string, string> > getCustomKeys();
 const string getName();
 const bool canRenameMultipleFiles();
 }
diff --git a/main.cpp b/main.cpp
index 86c5783..9b1a238 100644
--- a/main.cpp
+++ b/main.cpp
@@ -138,7 +138,7 @@ void getOptionsRest( const std::shared_ptr< restbed::Session > &session, rapidjs
     sendResponse(getOptionsJson(search), 200, session);
 }
 
-std::vector< std::string > getCustomKeys(size_t library_id) {
+std::vector< std::pair< std::string, std::string > > getCustomKeys(size_t library_id) {
     if(library_id >= libraries.size()) {
         return {};
     }
@@ -148,16 +148,16 @@ std::vector< std::string > getCustomKeys(size_t library_id) {
 
 std::string getCustomKeysJson(size_t library_id) {
     std::ostringstream res;
-    res << "{\n  \"custom_keys\": [\n";
+    res << "{\n  \"custom_keys\": {\n";
     auto custom_keys = getCustomKeys(library_id);
     if(!custom_keys.empty()) {
         for(auto &key : custom_keys) {
-            res << "\"" << safeJson(key) << "\",\n";
+            res << "\"" << safeJson(key.first) << "\": \"" << safeJson(key.second) << "\",\n";
         }
         res.seekp( -2, std::ios_base::end );
         res << "\n";
     }
-    res << "  ]\n}";
+    res << "  }\n}";
     return res.str();
 }
 
diff --git a/rename_library.hpp b/rename_library.hpp
index 7cfc6c1..82b7fdc 100644
--- a/rename_library.hpp
+++ b/rename_library.hpp
@@ -8,7 +8,7 @@ struct RenameLibrary {
     bool ( *init )( const std::string & );
     std::vector< RenameObject > ( *getOptions )( const RenameObject & );
     bool ( *renamePath )( const std::string &, const RenameObject & );
-    std::vector< std::string > ( *getCustomKeys )();
+    std::vector< std::pair< std::string, std::string > > ( *getCustomKeys )();
     const std::string ( *getName )();
     const bool ( *canRenameMultipleFiles )();
     void *libhndl;
diff --git a/simple_rename/simple.cpp b/simple_rename/simple.cpp
index a7a707b..261c484 100644
--- a/simple_rename/simple.cpp
+++ b/simple_rename/simple.cpp
@@ -22,11 +22,11 @@ constexpr const char_t *_tv_rename_dir_divider = "/";
 
 #endif
 
-bool init(const string &config_path) {
+bool init( const string &config_path ) {
     return true;
 }
 
-std::vector< RenameObject > getOptions( const RenameObject &/*UNUSED*/ ) {
+std::vector< RenameObject > getOptions( const RenameObject & /*UNUSED*/ ) {
     return {};
 }
 
@@ -40,14 +40,17 @@ bool renamePath( const string &path, const RenameObject &renamer ) {
         return false;
     }
 
-    if ( new_name.find('/') != string::npos || new_name.find('\\') != string::npos ) {
+    if ( new_name.find( '/' ) != string::npos ||
+         new_name.find( '\\' ) != string::npos ) {
         return false;
     }
-    return FSLib::rename( path, FSLib::canonical( FSLib::getContainingDirectory(path) ) + "/" + new_name );
+    return FSLib::rename(
+        path, FSLib::canonical( FSLib::getContainingDirectory( path ) ) + "/" +
+                  new_name );
 }
 
-std::vector< string > getCustomKeys() {
-    return { "new_name" };
+std::vector< std::pair< string, string > > getCustomKeys() {
+    return { { "new_name", STRING_TYPE } };
 }
 
 const string getName() {
diff --git a/themoviedb/moviedb.cpp b/themoviedb/moviedb.cpp
index a7102ea..6683eca 100644
--- a/themoviedb/moviedb.cpp
+++ b/themoviedb/moviedb.cpp
@@ -277,8 +277,12 @@ bool renamePath( const string &path, const RenameObject &renamer ) {
                         year );
 }
 
-std::vector< string > getCustomKeys() {
-    return { "id", "language", "year", "original_title", "use_original" };
+std::vector< std::pair< string, string > > getCustomKeys() {
+    return { { "id", NUM_TYPE },
+             { "language", STRING_TYPE },
+             { "year", YEAR_TYPE },
+             { "original_title", STRING_TYPE },
+             { "use_original", BOOL_TYPE } };
 }
 
 const string getName() {
diff --git a/thetvdb/tv_rename.cpp b/thetvdb/tv_rename.cpp
index 86c9170..e6faa0d 100644
--- a/thetvdb/tv_rename.cpp
+++ b/thetvdb/tv_rename.cpp
@@ -401,8 +401,11 @@ bool renamePath( const string &path, const RenameObject &renamer ) {
     return true;
 }
 
-std::vector< string > getCustomKeys() {
-    return { "id", "language", "pattern", "order" };
+std::vector< std::pair< string, string > > getCustomKeys() {
+    return { { "id", NUM_TYPE },
+             { "language", STRING_TYPE },
+             { "pattern", STRING_TYPE },
+             { "order", STRING_TYPE } };
 }
 
 const string getName() {