diff --git a/src/legacy/core_plugins/timelion/public/components/timelion_expression_input.tsx b/src/legacy/core_plugins/timelion/public/components/timelion_expression_input.tsx
index ed0b2dbb9e18f..f3d5fafc54b2a 100644
--- a/src/legacy/core_plugins/timelion/public/components/timelion_expression_input.tsx
+++ b/src/legacy/core_plugins/timelion/public/components/timelion_expression_input.tsx
@@ -82,6 +82,28 @@ function TimelionExpressionInput({
     [argValueSuggestions]
   );
 
+  const provideHover = useCallback(
+    async (model: monacoEditor.editor.ITextModel, position: monacoEditor.Position) => {
+      const suggestions = await suggest(
+        model.getValue(),
+        functionList.current,
+        // it's important to offset the cursor position on 1 point left
+        // because of PEG parser starts the line with 0, but monaco with 1
+        position.column - 1,
+        argValueSuggestions
+      );
+
+      return {
+        contents: suggestions
+          ? suggestions.list.map((s: ITimelionFunction | TimelionFunctionArgs) => ({
+              value: s.help,
+            }))
+          : [],
+      };
+    },
+    [argValueSuggestions]
+  );
+
   useEffect(() => {
     http.get('../api/timelion/functions').then(data => {
       functionList.current = data;
@@ -106,6 +128,7 @@ function TimelionExpressionInput({
               triggerCharacters: ['.', '(', '=', ':'],
               provideCompletionItems,
             }}
+            hoverProvider={{ provideHover }}
             options={{
               fontSize: 16,
               scrollBeyondLastLine: false,
diff --git a/src/legacy/core_plugins/timelion/public/components/timelion_interval.tsx b/src/legacy/core_plugins/timelion/public/components/timelion_interval.tsx
index e7cac126321fd..978c37b318d99 100644
--- a/src/legacy/core_plugins/timelion/public/components/timelion_interval.tsx
+++ b/src/legacy/core_plugins/timelion/public/components/timelion_interval.tsx
@@ -20,6 +20,7 @@
 import React, { useMemo } from 'react';
 import { EuiFormRow, EuiComboBox, EuiComboBoxOptionProps } from '@elastic/eui';
 import { i18n } from '@kbn/i18n';
+import { useValidation } from 'ui/vis/editors/default/controls/agg_utils';
 
 const intervalOptions = [
   {
@@ -69,9 +70,10 @@ const intervalOptions = [
 interface TimelionIntervalProps {
   value: string;
   setValue(value: string): void;
+  setValidity(valid: boolean): void;
 }
 
-function TimelionInterval({ value, setValue }: TimelionIntervalProps) {
+function TimelionInterval({ value, setValue, setValidity }: TimelionIntervalProps) {
   const onCustomInterval = (customValue: string) => {
     setValue(customValue.trim());
   };
@@ -85,6 +87,10 @@ function TimelionInterval({ value, setValue }: TimelionIntervalProps) {
     [value]
   );
 
+  const isValid = !!value;
+
+  useValidation(setValidity, isValid);
+
   return (
     <EuiFormRow
       compressed
@@ -92,16 +98,18 @@ function TimelionInterval({ value, setValue }: TimelionIntervalProps) {
       label={i18n.translate('timelion.vis.intervalLabel', {
         defaultMessage: 'Interval',
       })}
+      isInvalid={!isValid}
     >
       <EuiComboBox
         compressed
         fullWidth
+        isInvalid={!isValid}
         onChange={onChange}
         onCreateOption={onCustomInterval}
         options={intervalOptions}
         selectedOptions={selectedOptions}
         singleSelection={{ asPlainText: true }}
-        placeholder={i18n.translate('common.ui.aggTypes.timeInterval.selectIntervalPlaceholder', {
+        placeholder={i18n.translate('timelion.vis.selectIntervalPlaceholder', {
           defaultMessage: 'Select an interval',
         })}
       />
diff --git a/src/legacy/core_plugins/timelion/public/vis/timelion_options.tsx b/src/legacy/core_plugins/timelion/public/vis/timelion_options.tsx
index 9eee9ff512a5b..d23b10bf5f1ce 100644
--- a/src/legacy/core_plugins/timelion/public/vis/timelion_options.tsx
+++ b/src/legacy/core_plugins/timelion/public/vis/timelion_options.tsx
@@ -34,6 +34,7 @@ function TimelionOptions({
   stateParams,
   setValue,
   uiSettings,
+  setValidity,
 }: VisOptionsProps<VisParams> & TimelionExpressionInputDependencies) {
   const setInterval = useCallback((value: VisParams['interval']) => setValue('interval', value), [
     setValue,
@@ -45,7 +46,11 @@ function TimelionOptions({
 
   return (
     <EuiPanel paddingSize="s">
-      <TimelionInterval value={stateParams.interval} setValue={setInterval} />
+      <TimelionInterval
+        value={stateParams.interval}
+        setValue={setInterval}
+        setValidity={setValidity}
+      />
       <TimelionExpressionInput
         argValueSuggestions={argValueSuggestions}
         http={http}