diff --git a/src/components/FileExplorer.tsx b/src/components/FileExplorer.tsx
index 34ab421..0caa9ec 100644
--- a/src/components/FileExplorer.tsx
+++ b/src/components/FileExplorer.tsx
@@ -26,7 +26,6 @@ class FileExplorer extends React.Component<Props & ConnectorState> {
   static defaultProps: Partial<Props & ConnectorState> = {
     freeze: false,
     searchKey: '',
-    searched: false,
     visibleNodes: null,
   }
 
@@ -126,10 +125,9 @@ class FileExplorer extends React.Component<Props & ConnectorState> {
   })
 
   private renderActions: Node['props']['renderActions'] = node => {
-    const { searchKey, searched, goTo } = this.props
+    const { searchKey, goTo } = this.props
     return (
-      searchKey &&
-      searched && (
+      searchKey && (
         <button
           title={'Reveal in file tree'}
           className={'go-to-button'}
@@ -158,7 +156,7 @@ class FileExplorer extends React.Component<Props & ConnectorState> {
       visibleNodes,
       freeze,
       handleKeyDown,
-      handleSearchKeyChange,
+      search,
       toggleShowSettings,
       onFocusSearchBar,
       searchKey,
@@ -175,11 +173,7 @@ class FileExplorer extends React.Component<Props & ConnectorState> {
         ) : (
           visibleNodes && (
             <React.Fragment>
-              <SearchBar
-                searchKey={searchKey}
-                onSearchKeyChange={handleSearchKeyChange}
-                onFocus={onFocusSearchBar}
-              />
+              <SearchBar searchKey={searchKey} onSearch={search} onFocus={onFocusSearchBar} />
               {this.renderFiles(visibleNodes)}
             </React.Fragment>
           )
diff --git a/src/components/SearchBar.tsx b/src/components/SearchBar.tsx
index 1a59059..252b63a 100644
--- a/src/components/SearchBar.tsx
+++ b/src/components/SearchBar.tsx
@@ -1,24 +1,36 @@
 import * as React from 'react'
+import cx from 'utils/cx'
 
 type Props = {
-  onSearchKeyChange: React.FormEventHandler
+  onSearch: (searchKey: string) => void
   onFocus: React.FocusEventHandler
   searchKey: string
 }
 
-export default function SearchBar({ onSearchKeyChange, onFocus, searchKey }: Props) {
+export default function SearchBar({ onSearch, onFocus, searchKey }: Props) {
   return (
     <div className={'search-input-wrapper'}>
       <input
         onFocus={onFocus}
         tabIndex={0}
-        className="form-control search-input"
+        className={cx('form-control search-input', {
+          error: !isValidRegexpSource(searchKey),
+        })}
         aria-label="search files"
-        placeholder="Search files (RegEx)"
+        placeholder="Search files (use RegExp)"
         type="text"
-        onChange={onSearchKeyChange}
+        onChange={({ target: { value } }) => onSearch(value)}
         value={searchKey}
       />
     </div>
   )
 }
+
+function isValidRegexpSource(source: string) {
+  try {
+    new RegExp(source)
+    return true
+  } catch (err) {
+    return false
+  }
+}
diff --git a/src/content.less b/src/content.less
index 1300d06..1a7287a 100644
--- a/src/content.less
+++ b/src/content.less
@@ -306,6 +306,10 @@
           input[type='text'].form-control {
             box-shadow: none;
             width: 100%;
+
+            &.error {
+              border-color: #d73a49;
+            }
           }
         }
 
diff --git a/src/driver/core/FileExplorer.ts b/src/driver/core/FileExplorer.ts
index 36d7832..1b37705 100644
--- a/src/driver/core/FileExplorer.ts
+++ b/src/driver/core/FileExplorer.ts
@@ -4,7 +4,7 @@ import { GetCreatedMethod, MethodCreator } from 'driver/connect'
 import * as ini from 'ini'
 import { Base64 } from 'js-base64'
 import DOMHelper from 'utils/DOMHelper'
-import { findNode } from 'utils/general'
+import { findNode, searchKeyToRegexps } from 'utils/general'
 import GitHubHelper, { BlobData } from 'utils/GitHubHelper'
 import treeParser from 'utils/treeParser'
 import URLHelper from 'utils/URLHelper'
@@ -14,12 +14,12 @@ export type ConnectorState = {
   stateText: string
   visibleNodes: VisibleNodes | null
   searchKey: string
-  searched: boolean
+  searched: boolean // derived state from searchKey, = !!searchKey
 
   init: GetCreatedMethod<typeof init>
   execAfterRender: GetCreatedMethod<typeof execAfterRender>
   handleKeyDown: GetCreatedMethod<typeof handleKeyDown>
-  handleSearchKeyChange: GetCreatedMethod<typeof handleSearchKeyChange>
+  search: GetCreatedMethod<typeof search>
   onNodeClick: GetCreatedMethod<typeof onNodeClick>
   onFocusSearchBar: GetCreatedMethod<typeof onFocusSearchBar>
   setUpTree: GetCreatedMethod<typeof setUpTree>
@@ -150,7 +150,7 @@ const setUpTree: BoundMethodCreator<
     compress: compressSingletonFolder,
   })
 
-  await visibleNodesGenerator.init()
+  visibleNodesGenerator.init()
 
   tasksAfterRender.push(DOMHelper.focusSearchInput)
   dispatch.call(setStateText, '')
@@ -278,28 +278,15 @@ const handleKeyDown: BoundMethodCreator<[React.KeyboardEvent]> = dispatch => eve
 
 const onFocusSearchBar: BoundMethodCreator = dispatch => () => dispatch.call(focusNode, null, false)
 
-const handleSearchKeyChange: BoundMethodCreator<
-  [React.FormEvent<HTMLInputElement>]
-> = dispatch => async event => {
-  const searchKey = event.currentTarget.value
-  await dispatch.call(search, searchKey)
-}
-
-const search: BoundMethodCreator<[string]> = dispatch => {
-  let i = 0
-  return async searchKey => {
-    dispatch.set({ searchKey })
-    const j = (i += 1)
-    await visibleNodesGenerator.search(searchKey)
-    if (i === j) {
-      dispatch.set(({ searched }) => ({ searched: !(searched && searchKey === '') }))
-      dispatch.call(updateVisibleNodes)
-    }
-  }
+const search: BoundMethodCreator<[string]> = dispatch => searchKey => {
+  dispatch.set({ searchKey, searched: searchKey !== '' })
+  const regexps = searchKeyToRegexps(searchKey)
+  visibleNodesGenerator.search(regexps)
+  dispatch.call(updateVisibleNodes)
 }
 
 const goTo: BoundMethodCreator<[string[]]> = dispatch => async currentPath => {
-  await visibleNodesGenerator.search('')
+  visibleNodesGenerator.search([])
   tasksAfterRender.push(() => {
     const nodeExpandedTo = visibleNodesGenerator.expandTo(currentPath.join('/'))
     if (nodeExpandedTo) {
@@ -360,7 +347,6 @@ export default {
   handleKeyDown,
   onFocusSearchBar,
   search,
-  handleSearchKeyChange,
   setExpand,
   goTo,
   toggleNodeExpansion,
diff --git a/src/utils/cx.ts b/src/utils/cx.ts
index 7f44544..be8031f 100644
--- a/src/utils/cx.ts
+++ b/src/utils/cx.ts
@@ -9,9 +9,7 @@ export default function cx(...classNames: any[]): string {
         case 'string':
           return className
         case 'object':
-          return cx(
-            ...Object.entries(className).map(([key, value]) => (Boolean(value) ? key : null)),
-          )
+          return cx(...Object.entries(className).map(([key, value]) => (value ? key : null)))
         default:
           return ''
       }
diff --git a/src/utils/general.ts b/src/utils/general.ts
index 742e08a..9161a75 100644
--- a/src/utils/general.ts
+++ b/src/utils/general.ts
@@ -128,3 +128,14 @@ export async function JSONRequest(url: string, data: any, method = 'post') {
     body: JSON.stringify(data),
   })).json()
 }
+
+export function searchKeyToRegexps(searchKey: string) {
+  if (!searchKey) return []
+
+  try {
+    // case-sensitive when searchKey contains uppercase char
+    return [new RegExp(searchKey, /[A-Z]/i.test(searchKey) ? '' : 'i')]
+  } catch (err) {
+    return [/$^/] // matching nothing if failed transforming regexp
+  }
+}
diff --git a/src/utils/visibleNodesGenerator.ts b/src/utils/visibleNodesGenerator.ts
index 164bbf7..5212889 100644
--- a/src/utils/visibleNodesGenerator.ts
+++ b/src/utils/visibleNodesGenerator.ts
@@ -31,41 +31,15 @@ export type TreeNode = {
   accessDenied?: boolean
 }
 
-function getFilterFunc(keyRegex: RegExp) {
-  return function filterFunc({ name }: TreeNode) {
-    return keyRegex.test(name)
-  }
-}
-
 function filterDuplications<T>(arr: T[]) {
   return Array.from(new Set(arr))
 }
 
-function search(treeNodes: TreeNode[], searchKey: string): TreeNode[] {
-  if (!searchKey) return treeNodes
-  /**
-   * if searchKey is 'abcd'
-   * then keyRegex will be /abcd/i and /a.*?b.*?c.*?d/i
-   */
-  const regexpGenerators: ((raw: string) => RegExp)[] = [
-    raw => new RegExp(raw, 'i'),
-    raw => new RegExp(raw.split('').join('.*?'), 'i'),
-  ]
-
-  const keyRegexes: RegExp[] = []
-  for (const generator of regexpGenerators) {
-    try {
-      const regExp = generator(searchKey)
-      if (keyRegexes.find(keyRegex => keyRegex.source === regExp.source)) continue
-      // prevent duplicated regExp
-      keyRegexes.push(regExp)
-    } catch (err) {
-      // ignore invalid regexp
-    }
-  }
+function search(treeNodes: TreeNode[], regexps: RegExp[]): TreeNode[] {
+  if (!regexps.length) return treeNodes
 
   const searchResults = ([] as TreeNode[]).concat(
-    ...keyRegexes.map(keyRegex => treeNodes.filter(getFilterFunc(keyRegex))),
+    ...regexps.map(keyRegex => treeNodes.filter(({ name }) => keyRegex.test(name))),
   )
   return filterDuplications(searchResults)
 }
@@ -121,10 +95,10 @@ class L2 {
     this.searchedNodes = null
   }
 
-  search = async (searchKey: string) => {
-    this.compressed = !searchKey
-    this.searchedNodes = searchKey
-      ? search(this.l1.nodes, searchKey)
+  search = (regexps: RegExp[]) => {
+    this.compressed = !regexps.length
+    this.searchedNodes = regexps.length
+      ? search(this.l1.nodes, regexps)
       : this.getRoot().contents || []
   }
 
@@ -246,8 +220,8 @@ export default class VisibleNodesGenerator {
     this.l3 = new L3(this.l1, this.l2)
     this.l4 = new L4(this.l1, this.l2, this.l3)
 
-    this.search = async (...args) => {
-      const r = await this.l2.search(...args)
+    this.search = (...args) => {
+      const r = this.l2.search(...args)
       this.l3.generateVisibleNodes()
       this.l4.focusNode(null)
       return r
@@ -258,8 +232,8 @@ export default class VisibleNodesGenerator {
     this.focusNode = (...args) => this.l4.focusNode(...args)
   }
 
-  async init() {
-    await this.l2.search('')
+  init() {
+    this.l2.search([])
     this.l3.generateVisibleNodes()
   }