diff --git a/x-pack/plugins/apm/public/components/app/ServiceDetails/MetricsChart.tsx b/x-pack/plugins/apm/public/components/app/ServiceDetails/MetricsChart.tsx
index 346e6640286f3..d652e7c1bd8c6 100644
--- a/x-pack/plugins/apm/public/components/app/ServiceDetails/MetricsChart.tsx
+++ b/x-pack/plugins/apm/public/components/app/ServiceDetails/MetricsChart.tsx
@@ -5,7 +5,7 @@
  */
 import { EuiTitle } from '@elastic/eui';
 import React from 'react';
-import { GenericMetricsChart } from '../../../../server/lib/metrics/types';
+import { GenericMetricsChart } from '../../../../server/lib/metrics/transform_metrics_chart';
 // @ts-ignore
 import CustomPlot from '../../shared/charts/CustomPlot';
 import { HoverXHandlers } from '../../shared/charts/SyncChartGroup';
diff --git a/x-pack/plugins/apm/server/lib/metrics/get_metrics_chart_data_by_agent.ts b/x-pack/plugins/apm/server/lib/metrics/get_metrics_chart_data_by_agent.ts
index 6f9a8d6b0fc26..02b94c515d841 100644
--- a/x-pack/plugins/apm/server/lib/metrics/get_metrics_chart_data_by_agent.ts
+++ b/x-pack/plugins/apm/server/lib/metrics/get_metrics_chart_data_by_agent.ts
@@ -6,7 +6,7 @@
 import { Setup } from '../helpers/setup_request';
 import { getJavaMetricsCharts } from './by_agent/java';
 import { getDefaultMetricsCharts } from './by_agent/default';
-import { GenericMetricsChart } from './types';
+import { GenericMetricsChart } from './transform_metrics_chart';
 
 export interface MetricsChartsByAgentAPIResponse {
   charts: GenericMetricsChart[];
@@ -20,7 +20,7 @@ export async function getMetricsChartDataByAgent({
   setup: Setup;
   serviceName: string;
   agentName: string;
-}) {
+}): Promise<MetricsChartsByAgentAPIResponse> {
   switch (agentName) {
     case 'java': {
       return getJavaMetricsCharts(setup, serviceName);
diff --git a/x-pack/plugins/apm/server/lib/metrics/transform_metrics_chart.ts b/x-pack/plugins/apm/server/lib/metrics/transform_metrics_chart.ts
index ba3ec0a3a8383..951f4ff919a9a 100644
--- a/x-pack/plugins/apm/server/lib/metrics/transform_metrics_chart.ts
+++ b/x-pack/plugins/apm/server/lib/metrics/transform_metrics_chart.ts
@@ -5,7 +5,7 @@
  */
 import { AggregationSearchResponse } from 'elasticsearch';
 import theme from '@elastic/eui/dist/eui_theme_light.json';
-import { ChartBase, Chart, MetricsAggs, MetricsKeys } from './types';
+import { ChartBase, MetricsAggs, MetricsKeys } from './types';
 
 const colors = [
   theme.euiColorVis0,
@@ -17,6 +17,7 @@ const colors = [
   theme.euiColorVis6
 ];
 
+export type GenericMetricsChart = ReturnType<typeof transformDataToChart>;
 export function transformDataToChart<T extends MetricsKeys>(
   result: AggregationSearchResponse<void, MetricsAggs<T>>,
   chartBase: ChartBase<T>
@@ -24,8 +25,10 @@ export function transformDataToChart<T extends MetricsKeys>(
   const { aggregations, hits } = result;
   const { timeseriesData } = aggregations;
 
-  const chart: Chart<T> = {
-    ...chartBase,
+  return {
+    title: chartBase.title,
+    key: chartBase.key,
+    yUnit: chartBase.yUnit,
     totalHits: hits.total,
     series: Object.keys(chartBase.series).map((seriesKey, i) => ({
       title: chartBase.series[seriesKey].title,
@@ -43,6 +46,4 @@ export function transformDataToChart<T extends MetricsKeys>(
       })
     }))
   };
-
-  return chart;
 }
diff --git a/x-pack/plugins/apm/server/lib/metrics/types.ts b/x-pack/plugins/apm/server/lib/metrics/types.ts
index 15d54e1dd3fe5..7c22ddc73f553 100644
--- a/x-pack/plugins/apm/server/lib/metrics/types.ts
+++ b/x-pack/plugins/apm/server/lib/metrics/types.ts
@@ -5,61 +5,36 @@
  */
 
 import { ChartType, YUnit } from '../../../typings/timeseries';
-import { Coordinate } from '../../../typings/timeseries';
 
 export interface AggValue {
   value: number | null;
 }
 
-export interface TimeSeriesBucket {
-  key_as_string: string; // timestamp as string
-  key: number; // timestamp as epoch milliseconds
-  doc_count: number;
-}
-
 export interface MetricsKeys {
   [key: string]: AggValue;
 }
 
-interface SeriesDetails {
-  title: string;
-  color?: string;
-}
-
-type SeriesDetailsMap<T extends MetricsKeys> = {
-  [key in keyof T]: SeriesDetails
-};
-
 export interface ChartBase<T extends MetricsKeys> {
   title: string;
   key: string;
   type: ChartType;
   yUnit: YUnit;
-  transformValue?: (value: number) => number;
-  series: SeriesDetailsMap<T>;
-}
-
-export interface Chart<T extends MetricsKeys> {
-  title: ChartBase<T>['title'];
-  key: ChartBase<T>['key'];
-  type: ChartBase<T>['type'];
-  yUnit: ChartBase<T>['yUnit'];
-  totalHits: number;
-  series: Array<ChartSeries<T>>;
-}
-
-export type GenericMetricsChart = Chart<MetricsKeys>;
-
-export interface ChartSeries<T extends MetricsKeys> {
-  title: string;
-  key: keyof T;
-  type: ChartType;
-  overallValue: number | null;
-  data: Coordinate[];
+  series: {
+    [key in keyof T]: {
+      title: string;
+      color?: string;
+    }
+  };
 }
 
 export type MetricsAggs<T extends MetricsKeys> = {
   timeseriesData: {
-    buckets: Array<TimeSeriesBucket & T>;
+    buckets: Array<
+      {
+        key_as_string: string; // timestamp as string
+        key: number; // timestamp as epoch milliseconds
+        doc_count: number;
+      } & T
+    >;
   };
 } & T;