diff --git a/standalone_app/src/components/StorageProvider.tsx b/standalone_app/src/components/StorageProvider.tsx
index ac6019c5c..f47676005 100644
--- a/standalone_app/src/components/StorageProvider.tsx
+++ b/standalone_app/src/components/StorageProvider.tsx
@@ -1,5 +1,6 @@
 import { JournalFileStorage } from "@optuna/storage"
 import { SQLite3Storage } from "@optuna/storage"
+import type { OptunaStorage } from "@optuna/storage"
 import React, { FC, createContext, useState } from "react"
 
 export const StorageContext = createContext<{
diff --git a/standalone_app/src/components/StudyDetail.tsx b/standalone_app/src/components/StudyDetail.tsx
index 4c60e0e5b..b5366554a 100644
--- a/standalone_app/src/components/StudyDetail.tsx
+++ b/standalone_app/src/components/StudyDetail.tsx
@@ -33,7 +33,7 @@ export const StudyDetail: FC<{
   const idxNumber = parseInt(idx || "", 10)
 
   const { storage } = useContext(StorageContext)
-  const [study, setStudy] = useState<Study | null>(null)
+  const [study, setStudy] = useState<Optuna.Study | null>(null)
   useEffect(() => {
     const fetchStudy = async () => {
       if (storage === null) {
diff --git a/standalone_app/src/components/StudyList.tsx b/standalone_app/src/components/StudyList.tsx
index 4119747f7..e12274970 100644
--- a/standalone_app/src/components/StudyList.tsx
+++ b/standalone_app/src/components/StudyList.tsx
@@ -19,6 +19,7 @@ import {
   useTheme,
 } from "@mui/material"
 import { styled } from "@mui/system"
+import * as Optuna from "@optuna/types"
 import React, {
   FC,
   useEffect,
@@ -36,7 +37,7 @@ export const StudyList: FC<{
 }> = ({ toggleColorMode }) => {
   const theme = useTheme()
   const { storage } = useContext(StorageContext)
-  const [studies, setStudies] = useState<StudySummary[]>([])
+  const [studies, setStudies] = useState<Optuna.StudySummary[]>([])
 
   const [_studyFilterText, setStudyFilterText] = useState<string>("")
   const [sortBy, setSortBy] = useState<"id-asc" | "id-desc">("id-asc")
@@ -52,7 +53,7 @@ export const StudyList: FC<{
     fetchStudies()
   }, [storage])
   const filteredStudies = useMemo(() => {
-    const studyFilter = (row: StudySummary): boolean => {
+    const studyFilter = (row: Optuna.StudySummary): boolean => {
       const keywords = studyFilterText.split(" ")
       return !keywords.every((k) => {
         if (k === "") {
@@ -61,7 +62,9 @@ export const StudyList: FC<{
         return row.study_name.indexOf(k) >= 0
       })
     }
-    let filteredStudies: StudySummary[] = studies.filter((s) => !studyFilter(s))
+    let filteredStudies: Optuna.StudySummary[] = studies.filter(
+      (s) => !studyFilter(s)
+    )
     if (sortBy === "id-desc") {
       filteredStudies = filteredStudies.reverse()
     }
diff --git a/standalone_app/src/types/index.d.ts b/standalone_app/src/types/index.d.ts
index eb1f7e597..c07d8188f 100644
--- a/standalone_app/src/types/index.d.ts
+++ b/standalone_app/src/types/index.d.ts
@@ -1,99 +1 @@
 declare const IS_VSCODE: boolean
-
-type TrialState = "Running" | "Complete" | "Pruned" | "Fail" | "Waiting"
-type TrialStateFinished = "Complete" | "Fail" | "Pruned"
-type StudyDirection = "maximize" | "minimize"
-
-type OptunaStorage = {
-  getStudies: () => Promise<StudySummary[]>
-  getStudy: (idx: number) => Promise<Study | null>
-}
-
-type FloatDistribution = {
-  type: "FloatDistribution"
-  low: number
-  high: number
-  step: number | null
-  log: boolean
-}
-
-type IntDistribution = {
-  type: "IntDistribution"
-  low: number
-  high: number
-  step: number | null
-  log: boolean
-}
-
-type CategoricalChoiceType = null | boolean | number | string
-type CategoricalDistribution = {
-  type: "CategoricalDistribution"
-  choices: CategoricalChoiceType[]
-}
-
-type TrialIntermediateValue = {
-  step: number
-  value: number
-}
-
-type Distribution =
-  | FloatDistribution
-  | IntDistribution
-  | CategoricalDistribution
-
-type Attribute = {
-  key: string
-  value: string
-}
-
-type AttributeSpec = {
-  key: string
-  sortable: boolean
-}
-
-type StudySummary = {
-  study_id: number
-  study_name: string
-  directions: StudyDirection[]
-}
-
-type Study = {
-  study_id: number
-  study_name: string
-  directions: StudyDirection[]
-  union_search_space: SearchSpaceItem[]
-  intersection_search_space: SearchSpaceItem[]
-  union_user_attrs: AttributeSpec[]
-  datetime_start?: Date
-  trials: Trial[]
-}
-
-type Trial = {
-  trial_id: number
-  number: number
-  study_id: number
-  state: TrialState
-  values?: number[]
-  params: TrialParam[]
-  intermediate_values: TrialIntermediateValue[]
-  user_attrs: Attribute[]
-  datetime_start?: Date
-  datetime_complete?: Date
-}
-
-type TrialParam = {
-  name: string
-  param_internal_value: number
-  param_external_value: CategoricalChoiceType
-  param_external_type: string
-  distribution: Distribution
-}
-
-type SearchSpaceItem = {
-  name: string
-}
-
-type ParamImportance = {
-  name: string
-  importance: number
-}
diff --git a/tslib/storage/src/index.ts b/tslib/storage/src/index.ts
index fe384d10a..ad8afcd5b 100644
--- a/tslib/storage/src/index.ts
+++ b/tslib/storage/src/index.ts
@@ -1,2 +1,3 @@
 export { JournalFileStorage } from "./journal"
 export { SQLite3Storage } from "./sqlite"
+export type { OptunaStorage } from "./storage"