diff --git a/src/ast_values.cpp b/src/ast_values.cpp
index 8d9c40c..ae5aa6c 100644
--- a/src/ast_values.cpp
+++ b/src/ast_values.cpp
@@ -33,26 +33,51 @@
 {
 }
 
+bool module_::operator<(const module_& b) const
+{
+    return this->m_name < b.m_name;
+}
+
 bool identityRef_::operator==(const identityRef_& b) const
 {
     return this->m_prefix == b.m_prefix && this->m_value == b.m_value;
 }
 
+bool identityRef_::operator<(const identityRef_& b) const
+{
+    return std::tie(this->m_prefix, this->m_value) < std::tie(b.m_prefix, b.m_value);
+}
+
 bool binary_::operator==(const binary_& b) const
 {
     return this->m_value == b.m_value;
 }
 
+bool binary_::operator<(const binary_& b) const
+{
+    return this->m_value < b.m_value;
+}
+
 bool enum_::operator==(const enum_& b) const
 {
     return this->m_value == b.m_value;
 }
 
+bool enum_::operator<(const enum_& b) const
+{
+    return this->m_value < b.m_value;
+}
+
 bool special_::operator==(const special_& b) const
 {
     return this->m_value == b.m_value;
 }
 
+bool special_::operator<(const special_& b) const
+{
+    return this->m_value < b.m_value;
+}
+
 std::string specialValueToString(const special_& value)
 {
     switch (value.m_value) {
diff --git a/src/ast_values.hpp b/src/ast_values.hpp
index b2f2c3a..b79ac84 100644
--- a/src/ast_values.hpp
+++ b/src/ast_values.hpp
@@ -14,6 +14,7 @@
     enum_();
     enum_(const std::string& value);
     bool operator==(const enum_& b) const;
+    bool operator<(const enum_& b) const;
     std::string m_value;
 };
 
@@ -21,11 +22,13 @@
     binary_();
     binary_(const std::string& value);
     bool operator==(const binary_& b) const;
+    bool operator<(const binary_& b) const;
     std::string m_value;
 };
 
 struct module_ {
     bool operator==(const module_& b) const;
+    bool operator<(const module_& b) const;
     std::string m_name;
 };
 
@@ -34,6 +37,7 @@
     identityRef_(const std::string& module, const std::string& value);
     identityRef_(const std::string& value);
     bool operator==(const identityRef_& b) const;
+    bool operator<(const identityRef_& b) const;
     boost::optional<module_> m_prefix;
     std::string m_value;
 };
@@ -46,6 +50,7 @@
 
 struct special_ {
     bool operator==(const special_& b) const;
+    bool operator<(const special_& b) const;
     SpecialValue m_value;
 };
 
diff --git a/src/data_query.cpp b/src/data_query.cpp
new file mode 100644
index 0000000..be979ff
--- /dev/null
+++ b/src/data_query.cpp
@@ -0,0 +1,18 @@
+#include "data_query.hpp"
+#include "datastore_access.hpp"
+#include "schema.hpp"
+#include "utils.hpp"
+
+
+DataQuery::DataQuery(DatastoreAccess& datastore)
+    : m_datastore(datastore)
+{
+    m_schema = m_datastore.schema();
+}
+
+std::vector<ListInstance> DataQuery::listKeys(const dataPath_& location, const ModuleNodePair& node) const
+{
+    auto listPath = joinPaths(pathToDataString(location, Prefixes::Always), fullNodeName(location, node));
+
+    return m_datastore.listInstances(listPath);
+}
diff --git a/src/data_query.hpp b/src/data_query.hpp
new file mode 100644
index 0000000..b2f4a33
--- /dev/null
+++ b/src/data_query.hpp
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2019 CESNET, https://photonics.cesnet.cz/
+ *
+ * Written by Václav Kubernát <kubernat@cesnet.cz>
+ *
+*/
+
+#pragma once
+
+#include <boost/optional.hpp>
+#include <map>
+#include <memory>
+#include <set>
+#include "ast_values.hpp"
+#include "datastore_access.hpp"
+#include "schema.hpp"
+
+
+/*! \class DataQuery
+ *  \brief A class used for querying data from a datastore for usage in tab-completion.
+ *
+*/
+class DataQuery {
+public:
+    DataQuery(DatastoreAccess& datastore);
+    /*! \brief Lists all possible instances of key/value pairs for a list specified by the arguments.
+     *  \param location Location of the list.
+     *  \param node Name (and optional module name) of the list.
+     *  \return A vector of maps, which represent the instances. The map is keyed by the name of the list key. The values in the map, are values of the list keys.
+     */
+    std::vector<ListInstance> listKeys(const dataPath_& location, const ModuleNodePair& node) const;
+
+private:
+    DatastoreAccess& m_datastore;
+    std::shared_ptr<Schema> m_schema;
+};
diff --git a/src/datastore_access.hpp b/src/datastore_access.hpp
index ae0d12a..6686b92 100644
--- a/src/datastore_access.hpp
+++ b/src/datastore_access.hpp
@@ -36,6 +36,8 @@
 
 class Schema;
 
+using ListInstance = std::map<std::string, leaf_data_>;
+
 class DatastoreAccess {
 public:
     using Tree = std::map<std::string, leaf_data_>;
@@ -52,4 +54,8 @@
 
     virtual void commitChanges() = 0;
     virtual void discardChanges() = 0;
+
+private:
+    friend class DataQuery;
+    virtual std::vector<ListInstance> listInstances(const std::string& path) = 0;
 };
diff --git a/src/netconf_access.cpp b/src/netconf_access.cpp
index 7387231..91b1874 100644
--- a/src/netconf_access.cpp
+++ b/src/netconf_access.cpp
@@ -194,3 +194,36 @@
 {
     return m_schema;
 }
+
+std::vector<ListInstance> NetconfAccess::listInstances(const std::string& path)
+{
+    std::vector<ListInstance> res;
+    auto list = m_schema->dataNodeFromPath(path);
+
+    // This inserts selection nodes - I only want keys not other data
+    // To get the keys, I have to call find_path here - otherwise I would get keys of a top-level node (which might not even be a list)
+    auto keys = libyang::Schema_Node_List{(*(list->find_path(path.c_str())->data().begin()))->schema()}.keys();
+    for (const auto& keyLeaf : keys) {
+        // Have to call find_path here - otherwise I'll have the list, not the leaf inside it
+        auto selectionLeaf = *(m_schema->dataNodeFromPath(keyLeaf->path())->find_path(keyLeaf->path().c_str())->data().begin());
+        auto actualList = *(list->find_path(path.c_str())->data().begin());
+        actualList->insert(selectionLeaf);
+    }
+
+    auto instances = m_session->getConfig(NC_DATASTORE_RUNNING, list->print_mem(LYD_XML, 0));
+
+
+    for (const auto& instance : instances->find_path(path.c_str())->data()) {
+        ListInstance instanceRes;
+
+        // I take the first child here, because the first element (the parent of the child()) will be the list
+        for (const auto& keyLeaf : instance->child()->tree_for()) {
+            auto leafData = libyang::Data_Node_Leaf_List{keyLeaf};
+            auto leafSchema = libyang::Schema_Node_Leaf{leafData.schema()};
+            instanceRes.insert({ leafSchema.name(), leafValueFromValue(leafData.value(), leafSchema.type()->base())});
+        }
+        res.push_back(instanceRes);
+    }
+
+    return res;
+}
diff --git a/src/netconf_access.hpp b/src/netconf_access.hpp
index f43976a..aa13312 100644
--- a/src/netconf_access.hpp
+++ b/src/netconf_access.hpp
@@ -46,6 +46,8 @@
     std::shared_ptr<Schema> schema() override;
 
 private:
+    std::vector<std::map<std::string, leaf_data_>> listInstances(const std::string& path) override;
+
     std::string fetchSchema(const std::string_view module, const
             std::optional<std::string_view> revision, const
             std::optional<std::string_view> submodule, const
diff --git a/src/sysrepo_access.cpp b/src/sysrepo_access.cpp
index cf19407..b681893 100644
--- a/src/sysrepo_access.cpp
+++ b/src/sysrepo_access.cpp
@@ -6,7 +6,10 @@
  *
 */
 
+#include <libyang/Tree_Data.hpp>
+#include <libyang/Tree_Schema.hpp>
 #include <sysrepo-cpp/Session.hpp>
+#include "libyang_utils.hpp"
 #include "sysrepo_access.hpp"
 #include "utils.hpp"
 #include "yang_schema.hpp"
@@ -317,3 +320,54 @@
 
     throw DatastoreException(res);
 }
+
+std::vector<ListInstance> SysrepoAccess::listInstances(const std::string& path)
+{
+    std::vector<ListInstance> res;
+    auto lists = getItems(path);
+
+    decltype(lists) instances;
+    auto wantedTree = *(m_schema->dataNodeFromPath(path)->find_path(path.c_str())->data().begin());
+    std::copy_if(lists.begin(), lists.end(), std::inserter(instances, instances.end()), [this, pathToCheck=wantedTree->schema()->path()](const auto& item) {
+        // This filters out non-instances.
+        if (item.second.type() != typeid(special_) || boost::get<special_>(item.second).m_value != SpecialValue::List) {
+            return false;
+        }
+
+        // Now, getItems is recursive: it gives everything including nested lists. So I try create a tree from the instance...
+        auto instanceTree = *(m_schema->dataNodeFromPath(item.first)->find_path(item.first.c_str())->data().begin());
+        // And then check if its schema path matches the list we actually want. This filters out lists which are not the ones I requested.
+        return instanceTree->schema()->path() == pathToCheck;
+    });
+
+    // If there are no instances, then just return
+    if (instances.empty()) {
+        return res;
+    }
+
+    // I need to find out which keys does the list have. To do that, I create a
+    // tree from the first instance. This is gives me some top level node,
+    // which will be our list in case out list is a top-level node. In case it
+    // isn't, we have call find_path on the top level node. After that, I just
+    // retrieve the keys.
+    auto topLevelTree = m_schema->dataNodeFromPath(instances.begin()->first);
+    auto list = *(topLevelTree->find_path(path.c_str())->data().begin());
+    auto keys = libyang::Schema_Node_List{list->schema()}.keys();
+
+    // Creating a full tree at the same time from the values sysrepo gives me
+    // would be a pain (and after sysrepo switches to libyang meaningless), so
+    // I just use this algorithm to create data nodes one by one and get the
+    // key values from them.
+    for (const auto& instance : instances) {
+        auto wantedList = *(m_schema->dataNodeFromPath(instance.first)->find_path(path.c_str())->data().begin());
+        ListInstance instanceRes;
+        for (const auto& key : keys) {
+            auto vec = wantedList->find_path(key->name())->data();
+            auto leaf = libyang::Data_Node_Leaf_List{*(vec.begin())};
+            instanceRes.emplace(key->name(), leafValueFromValue(leaf.value(), leaf.leaf_type()->base()));
+        }
+        res.push_back(instanceRes);
+    }
+
+    return res;
+}
diff --git a/src/sysrepo_access.hpp b/src/sysrepo_access.hpp
index c2ce909..cebb564 100644
--- a/src/sysrepo_access.hpp
+++ b/src/sysrepo_access.hpp
@@ -42,6 +42,7 @@
     void discardChanges() override;
 
 private:
+    std::vector<std::map<std::string, leaf_data_>> listInstances(const std::string& path) override;
     [[noreturn]] void reportErrors();
 
     std::string fetchSchema(const char* module, const char* revision, const char* submodule);
diff --git a/src/yang_schema.cpp b/src/yang_schema.cpp
index 06259b9..999f33a 100644
--- a/src/yang_schema.cpp
+++ b/src/yang_schema.cpp
@@ -399,7 +399,7 @@
                                                 path.c_str(),
                                                 value ? value.value().c_str() : nullptr,
                                                 LYD_ANYDATA_CONSTSTRING,
-                                                0);
+                                                LYD_PATH_OPT_EDIT);
 }
 
 std::shared_ptr<libyang::Module> YangSchema::getYangModule(const std::string& name)