diff --git a/frontend/components/ui/index.ts b/frontend/components/ui/index.ts
index 7ef1810..4e9c228 100644
--- a/frontend/components/ui/index.ts
+++ b/frontend/components/ui/index.ts
@@ -9,6 +9,7 @@ export {
   DefinitionList,
   EmptyTableBody,
   FONT_FAMILY,
+  FaCircleInfoIcon,
   FaCirclePlusIcon,
   FaGearIcon,
   FaPencilIcon,
@@ -31,7 +32,9 @@ export {
   TableReel,
   Td,
   Text,
+  Textarea,
   Th,
+  Tooltip,
   UnstyledButton,
   createTheme,
   defaultBorder,
diff --git a/frontend/constants/path.ts b/frontend/constants/path.ts
index cdddc40..33e9415 100644
--- a/frontend/constants/path.ts
+++ b/frontend/constants/path.ts
@@ -26,6 +26,9 @@ export const path = {
     sources: {
       index: () => '/api/sources.json',
       show: (sourceName: string) => `/api/sources/${sourceName}.json`,
+      memo: {
+        update: (sourceName: string) => `/api/sources/${sourceName}/memo.json`,
+      },
       modules: {
         update: (sourceName: string) => `/api/sources/${sourceName}/modules.json`,
       },
diff --git a/frontend/models/combinedDefinition.ts b/frontend/models/combinedDefinition.ts
index d46ecd3..741eb10 100644
--- a/frontend/models/combinedDefinition.ts
+++ b/frontend/models/combinedDefinition.ts
@@ -1,4 +1,5 @@
 import { Module } from './module'
+import { Source } from './source'
 
 type BaseDotMetadata = {
   id: string
@@ -7,6 +8,7 @@ type BaseDotMetadata = {
 export type DotSourceMetadata = {
   type: 'source'
   sourceName: string
+  memo: string
   modules: Module[]
 } & BaseDotMetadata
 
@@ -34,10 +36,5 @@ export type CombinedDefinition = {
   titles: string[]
   dot: string
   dotMetadata: DotMetadata[]
-  sources: Array<{ sourceName: string; modules: Module[] }>
-}
-
-export type DotSource = {
-  type: 'source'
-  sourceName: string
+  sources: Source[]
 }
diff --git a/frontend/models/module.ts b/frontend/models/module.ts
index 7a2bfc6..640aed3 100644
--- a/frontend/models/module.ts
+++ b/frontend/models/module.ts
@@ -8,6 +8,7 @@ export type SpecificModule = {
   }>
   sources: Array<{
     sourceName: string
+    memo: string
   }>
   relatedDefinitions: Array<{
     id: number
diff --git a/frontend/models/source.ts b/frontend/models/source.ts
index b67a8a3..1717e64 100644
--- a/frontend/models/source.ts
+++ b/frontend/models/source.ts
@@ -3,6 +3,7 @@ import { Module } from './module'
 
 export type Source = {
   sourceName: string
+  memo: string
   modules: Module[]
 }
 
@@ -18,6 +19,7 @@ type ReverseDependency = {
 
 export type SpecificSource = {
   sourceName: string
+  memo: string
   modules: Module[]
   relatedDefinitions: RelatedDefinition[]
   reverseDependencies: ReverseDependency[]
@@ -48,10 +50,7 @@ export const sortSources = (sources: Source[], key: 'sourceName' | 'modules', so
     }
     case 'modules': {
       sorted = sorted.sort((a, b) =>
-        ascString(
-          a.modules.map((module) => module.moduleName).join('-'),
-          b.modules.map((module) => module.moduleName).join('-'),
-        ),
+        ascString(a.modules.map((module) => module.moduleName).join('-'), b.modules.map((module) => module.moduleName).join('-')),
       )
     }
   }
diff --git a/frontend/pages/DefinitionList/components/DefinitionList/List.tsx b/frontend/pages/DefinitionList/components/DefinitionList/List.tsx
index 3b1ae4b..979d4b5 100644
--- a/frontend/pages/DefinitionList/components/DefinitionList/List.tsx
+++ b/frontend/pages/DefinitionList/components/DefinitionList/List.tsx
@@ -82,9 +82,10 @@ export const List = forwardRef<HTMLLIElement, Props>((props, ref) => {
           }
 
           const isSelected = selectedDefinitionIds.includes(definition.id)
-          const countLabel = definition.unclassifiedSourcesCount === 0 ?
-            `(${definition.sourcesCount})` :
-            `(${definition.unclassifiedSourcesCount}/${definition.sourcesCount})`
+          const countLabel =
+            definition.unclassifiedSourcesCount === 0
+              ? `(${definition.sourcesCount})`
+              : `(${definition.unclassifiedSourcesCount}/${definition.sourcesCount})`
 
           items.push({
             key: `definition-${definition.id}`,
diff --git a/frontend/pages/DefinitionList/components/DefinitionSources/DefinitionSources.tsx b/frontend/pages/DefinitionList/components/DefinitionSources/DefinitionSources.tsx
index 0071e02..5906640 100644
--- a/frontend/pages/DefinitionList/components/DefinitionSources/DefinitionSources.tsx
+++ b/frontend/pages/DefinitionList/components/DefinitionSources/DefinitionSources.tsx
@@ -2,13 +2,27 @@ import { FC, useCallback, useMemo, useState } from 'react'
 import styled from 'styled-components'
 
 import { Link } from '@/components/Link'
-import { Aside, Button, Cluster, EmptyTableBody, FaPencilIcon, Table, TableReel, Td, Text, Th } from '@/components/ui'
+import {
+  Aside,
+  Button,
+  Cluster,
+  EmptyTableBody,
+  FaCircleInfoIcon,
+  FaPencilIcon,
+  Table,
+  TableReel,
+  Td,
+  Text,
+  Th,
+  Tooltip,
+} from '@/components/ui'
 import { path } from '@/constants/path'
 import { color } from '@/constants/theme'
 import { CombinedDefinition } from '@/models/combinedDefinition'
 
 import { SourceModulesComboBox } from '../SourceModulesComboBox'
 import { sortSources } from '@/models/source'
+import { SourceMemoInput } from '../SourceMemoInput'
 
 type Props = {
   combinedDefinition: CombinedDefinition
@@ -26,7 +40,8 @@ type SortState = {
 
 export const DefinitionSources: FC<Props> = ({ combinedDefinition, mutateCombinedDefinition }) => {
   const [sortState, setSortState] = useState<SortState>({ key: 'sourceName', sort: 'asc' })
-  const [editingSourceNames, setEditingSourceNames] = useState<string[]>([])
+  const [editingModulesSourceNames, setEditingModulesSourceNames] = useState<string[]>([])
+  const [editingMemoSourceNames, setEditingMemoSourceNames] = useState<string[]>([])
 
   const setNextSortType = useCallback(
     (key: SortState['key']) => {
@@ -58,6 +73,7 @@ export const DefinitionSources: FC<Props> = ({ combinedDefinition, mutateCombine
                 <Th sort={sortState.key === 'sourceName' ? sortState.sort : 'none'} onSort={() => setNextSortType('sourceName')}>
                   Source name
                 </Th>
+                <Th>Memo</Th>
                 <Th fixed sort={sortState.key === 'modules' ? sortState.sort : 'none'} onSort={() => setNextSortType('modules')}>
                   Modules
                 </Th>
@@ -75,17 +91,54 @@ export const DefinitionSources: FC<Props> = ({ combinedDefinition, mutateCombine
                     <Td>
                       <Link to={path.sources.show(source.sourceName)}>{source.sourceName}</Link>
                     </Td>
-                    {editingSourceNames.includes(source.sourceName) ? (
+                    <Td>
+                      {editingMemoSourceNames.includes(source.sourceName) ? (
+                        <SourceMemoInput
+                          sourceName={source.sourceName}
+                          initialMemo={source.memo}
+                          onUpdate={() => {
+                            setEditingMemoSourceNames((prev) => prev.filter((name) => name !== source.sourceName))
+                            mutateCombinedDefinition()
+                          }}
+                          onClose={() => {
+                            setEditingMemoSourceNames((prev) => prev.filter((name) => name !== source.sourceName))
+                          }}
+                        />
+                      ) : (
+                        <FixedWidthMemo align="center">
+                          {source.memo !== '' ? (
+                            <Tooltip message={source.memo} horizontal="center" vertical="bottom">
+                              <FaCircleInfoIcon />
+                            </Tooltip>
+                          ) : (
+                            <Transparent>
+                              <FaCircleInfoIcon />
+                            </Transparent>
+                          )}
+                          <div>
+                            <Button
+                              square={true}
+                              onClick={() => setEditingMemoSourceNames((prev) => [...prev, source.sourceName])}
+                              size="s"
+                            >
+                              <FaPencilIcon alt="Edit" />
+                            </Button>
+                          </div>
+                        </FixedWidthMemo>
+                      )}
+                    </Td>
+                    {!editingMemoSourceNames.includes(source.sourceName) &&
+                    editingModulesSourceNames.includes(source.sourceName) ? (
                       <Td fixed colSpan={2}>
                         <SourceModulesComboBox
                           sourceName={source.sourceName}
                           initialModules={source.modules}
                           onUpdate={() => {
-                            setEditingSourceNames((prev) => prev.filter((name) => name !== source.sourceName))
+                            setEditingModulesSourceNames((prev) => prev.filter((name) => name !== source.sourceName))
                             mutateCombinedDefinition()
                           }}
                           onClose={() => {
-                            setEditingSourceNames((prev) => prev.filter((name) => name !== source.sourceName))
+                            setEditingModulesSourceNames((prev) => prev.filter((name) => name !== source.sourceName))
                           }}
                         />
                       </Td>
@@ -104,7 +157,7 @@ export const DefinitionSources: FC<Props> = ({ combinedDefinition, mutateCombine
                           <div>
                             <Button
                               square={true}
-                              onClick={() => setEditingSourceNames((prev) => [...prev, source.sourceName])}
+                              onClick={() => setEditingModulesSourceNames((prev) => [...prev, source.sourceName])}
                               size="s"
                             >
                               <FaPencilIcon alt="Edit" />
@@ -141,6 +194,14 @@ const TableWrapper = styled.div`
   overflow-x: scroll;
 `
 
+const Transparent = styled.span`
+  opacity: 0;
+`
+
+const FixedWidthMemo = styled(Cluster)`
+  width: 4em;
+`
+
 const StyledTable = styled(Table)`
   border-left: 1px ${color.BORDER} solid;
 `
diff --git a/frontend/pages/DefinitionList/components/MetadataDialog/MetadataDialog.tsx b/frontend/pages/DefinitionList/components/MetadataDialog/MetadataDialog.tsx
index b209333..222d98f 100644
--- a/frontend/pages/DefinitionList/components/MetadataDialog/MetadataDialog.tsx
+++ b/frontend/pages/DefinitionList/components/MetadataDialog/MetadataDialog.tsx
@@ -2,13 +2,26 @@ import { ComponentProps, FC, useMemo, useState } from 'react'
 import styled from 'styled-components'
 
 import { Link } from '@/components/Link'
-import { Button, Cluster, DefinitionList, FaPencilIcon, Heading, ModelessDialog, Stack, Table, Td, Th } from '@/components/ui'
+import {
+  Button,
+  Cluster,
+  DefinitionList,
+  FaPencilIcon,
+  Heading,
+  ModelessDialog,
+  Stack,
+  Table,
+  Text,
+  Td,
+  Th,
+} from '@/components/ui'
 import { path } from '@/constants/path'
 import { spacing } from '@/constants/theme'
 import { DotDependencyMetadata, DotMetadata, DotModuleMetadata, DotSourceMetadata } from '@/models/combinedDefinition'
 
 import { SourceModulesComboBox } from '../SourceModulesComboBox'
 import { DialogProps } from '../dialog'
+import { SourceMemoInput } from '../SourceMemoInput'
 
 type Props = {
   dotMetadata: DotMetadata | null
@@ -25,11 +38,45 @@ const SourceDotMetadataContent: FC<{ metadata: DotSourceMetadata } & Pick<Props,
   mutateCombinedDefinition,
 }) => {
   const [editingModules, setEditingModules] = useState<boolean>(false)
+  const [editingMemo, setEditingMemo] = useState<boolean>(false)
   const items: ComponentProps<typeof DefinitionList>['items'] = [
     {
       term: 'Source Name',
       description: <Link to={path.sources.show(metadata.sourceName)}>{metadata.sourceName}</Link>,
     },
+    {
+      term: 'Memo',
+      description: (
+        <Cluster>
+          {editingMemo ? (
+            <SourceMemoInput
+              sourceName={metadata.sourceName}
+              initialMemo={metadata.memo}
+              onUpdate={() => {
+                setEditingMemo(false)
+                mutateCombinedDefinition()
+              }}
+              onClose={() => {
+                setEditingMemo(false)
+              }}
+            />
+          ) : (
+            <>
+              <Text>{metadata.memo}</Text>
+              <Button
+                square={true}
+                onClick={() => {
+                  setEditingMemo(true)
+                }}
+                size="s"
+              >
+                <FaPencilIcon alt="編集" />
+              </Button>
+            </>
+          )}
+        </Cluster>
+      ),
+    },
     {
       term: 'Modules',
       description: (
@@ -69,7 +116,7 @@ const SourceDotMetadataContent: FC<{ metadata: DotSourceMetadata } & Pick<Props,
     },
   ]
 
-  return <DefinitionList items={items} />
+  return <DefinitionList maxColumns={1} items={items} />
 }
 
 const DependencyDotMetadataContent: FC<{ metadata: DotDependencyMetadata }> = ({ metadata }) => (
@@ -132,7 +179,7 @@ export const MetadataDialog: FC<Props> = ({ dotMetadata, isOpen, onClose, top, l
   return (
     <ModelessDialog
       isOpen={!!(isOpen && dotMetadata)}
-      header={<ModelessHeading>Description</ModelessHeading>}
+      header={<ModelessHeading>Memo</ModelessHeading>}
       onClickClose={onClose}
       onPressEscape={onClose}
       top={top}
diff --git a/frontend/pages/DefinitionList/components/SourceMemoInput/SourceMemoInput.tsx b/frontend/pages/DefinitionList/components/SourceMemoInput/SourceMemoInput.tsx
new file mode 100644
index 0000000..0bc32b8
--- /dev/null
+++ b/frontend/pages/DefinitionList/components/SourceMemoInput/SourceMemoInput.tsx
@@ -0,0 +1,45 @@
+import React, { FC, useCallback, useEffect, useState } from 'react'
+
+import { Button, Cluster, FaXmarkIcon, FormControl, Input, Textarea } from '@/components/ui'
+import { useSourceMemo } from '@/repositories/sourceMemoRepository'
+
+type Props = {
+  sourceName: string
+  initialMemo: string
+  onClose: () => void
+  onUpdate: () => void
+}
+
+export const SourceMemoInput: FC<Props> = ({ sourceName, initialMemo, onClose, onUpdate }) => {
+  const { trigger } = useSourceMemo(sourceName)
+
+  const [memo, setMemo] = useState<string>(initialMemo)
+
+  const handleUpdate = useCallback(async () => {
+    await trigger({ memo })
+    onUpdate()
+  }, [trigger, memo, onUpdate])
+
+  const onInputMemo = useCallback(
+    (event: React.ChangeEvent<HTMLTextAreaElement | HTMLInputElement>) => {
+      setMemo(event.target.value)
+    },
+    [setMemo],
+  )
+
+  return (
+    <Cluster>
+      <div>
+        <FormControl title="Memo" helpMessage="Free memo field.">
+          <Textarea onChange={onInputMemo} value={memo} autoResize />
+        </FormControl>
+      </div>
+      <Button square={true} variant="primary" onClick={handleUpdate} size="s">
+        Update
+      </Button>
+      <Button square={true} onClick={onClose} size="s">
+        <FaXmarkIcon alt="Cancel" />
+      </Button>
+    </Cluster>
+  )
+}
diff --git a/frontend/pages/DefinitionList/components/SourceMemoInput/index.ts b/frontend/pages/DefinitionList/components/SourceMemoInput/index.ts
new file mode 100644
index 0000000..abb7ab4
--- /dev/null
+++ b/frontend/pages/DefinitionList/components/SourceMemoInput/index.ts
@@ -0,0 +1 @@
+export { SourceMemoInput } from './SourceMemoInput'
diff --git a/frontend/pages/DefinitionList/components/SourceModulesComboBox/SourceModulesComboBox.tsx b/frontend/pages/DefinitionList/components/SourceModulesComboBox/SourceModulesComboBox.tsx
index be29a13..9f0a361 100644
--- a/frontend/pages/DefinitionList/components/SourceModulesComboBox/SourceModulesComboBox.tsx
+++ b/frontend/pages/DefinitionList/components/SourceModulesComboBox/SourceModulesComboBox.tsx
@@ -1,7 +1,7 @@
 import React, { FC, useCallback, useMemo, useState } from 'react'
 import { ComboBoxItem } from 'smarthr-ui/lib/components/ComboBox/types'
 
-import { Button, Cluster, FaXmarkIcon, SingleComboBox, Text } from '@/components/ui'
+import { Button, Cluster, FaXmarkIcon, FormControl, Input, SingleComboBox, Text } from '@/components/ui'
 import { Module } from '@/models/module'
 import { useModules } from '@/repositories/moduleRepository'
 import { useSourceModules } from '@/repositories/sourceModulesRepository'
@@ -61,8 +61,8 @@ export const SourceModulesComboBox: FC<Props> = ({ sourceName, initialModules, o
     [setTemporaryItem, setSelectedItem],
   )
 
-  const handleUpdate = useCallback(() => {
-    trigger({ modules: selectedItem?.data ?? [] })
+  const handleUpdate = useCallback(async () => {
+    await trigger({ modules: selectedItem?.data ?? [] })
     mutate()
     onUpdate()
   }, [mutate, trigger, selectedItem, onUpdate])
@@ -80,22 +80,23 @@ export const SourceModulesComboBox: FC<Props> = ({ sourceName, initialModules, o
   return (
     <Cluster>
       <div>
-        <Text as="p">When entering the name of a module, please use the `/` character to separate the levels of hierarchy.</Text>
-        <SingleComboBox
-          items={items}
-          selectedItem={selectedItem}
-          dropdownHelpMessage="Select or input Module"
-          creatable
-          isLoading={isLoading}
-          onSelect={handleSelectItem}
-          onClear={handleClear}
-          onAdd={handleAddItem}
-          width="200px"
-          decorators={{
-            noResultText: () => `no result.`,
-            destroyButtonIconAlt: (text) => `destroy.(${text})`,
-          }}
-        />
+        <FormControl title="Modules" helpMessage="Submodules are separated by slash">
+          <SingleComboBox
+            items={items}
+            selectedItem={selectedItem}
+            dropdownHelpMessage="Select or input Module"
+            creatable
+            isLoading={isLoading}
+            onSelect={handleSelectItem}
+            onClear={handleClear}
+            onAdd={handleAddItem}
+            width="200px"
+            decorators={{
+              noResultText: () => `no result.`,
+              destroyButtonIconAlt: (text) => `destroy.(${text})`,
+            }}
+          />
+        </FormControl>
       </div>
       <Button square={true} variant="primary" onClick={handleUpdate} size="s">
         Update
diff --git a/frontend/pages/Modules/Show.tsx b/frontend/pages/Modules/Show.tsx
index 22039f6..346f1de 100644
--- a/frontend/pages/Modules/Show.tsx
+++ b/frontend/pages/Modules/Show.tsx
@@ -51,6 +51,7 @@ export const Show: React.FC = () => {
                       <thead>
                         <tr>
                           <Th>Source Name</Th>
+                          <Th>Memo</Th>
                         </tr>
                       </thead>
                       {specificModule.sources.length === 0 ? (
@@ -64,6 +65,11 @@ export const Show: React.FC = () => {
                               <Td>
                                 <Link to={path.sources.show(source.sourceName)}>{source.sourceName}</Link>
                               </Td>
+                              <Td>
+                                <Text>
+                                  {source.memo}
+                                </Text>
+                              </Td>
                             </tr>
                           ))}
                         </tbody>
diff --git a/frontend/pages/Sources/List.tsx b/frontend/pages/Sources/List.tsx
index 12b31dd..e2d115a 100644
--- a/frontend/pages/Sources/List.tsx
+++ b/frontend/pages/Sources/List.tsx
@@ -49,7 +49,12 @@ export const List: FC = () => {
   return (
     <StyledSection>
       <Stack>
-        <Heading type="screenTitle">Sources {data ? `(classified: ${Math.round(data.classifiedSourcesCount / data.sources.length * 100)}% ${data.classifiedSourcesCount} / ${data.sources.length})` : null}</Heading>
+        <Heading type="screenTitle">
+          Sources{' '}
+          {data
+            ? `(classified: ${Math.round((data.classifiedSourcesCount / data.sources.length) * 100)}% ${data.classifiedSourcesCount} / ${data.sources.length})`
+            : null}
+        </Heading>
 
         <div style={{ overflow: 'clip' }}>
           <Table fixedHead>
diff --git a/frontend/pages/Sources/Show.tsx b/frontend/pages/Sources/Show.tsx
index df64256..a6ae379 100644
--- a/frontend/pages/Sources/Show.tsx
+++ b/frontend/pages/Sources/Show.tsx
@@ -32,6 +32,15 @@ export const Show: React.FC = () => {
         <Section>
           {specificSource && !isLoading ? (
             <Stack gap={1.5}>
+              <Section>
+                <Stack gap={0.5}>
+                  <Heading type="sectionTitle">Memo</Heading>
+                  <div style={{ overflow: 'clip' }}>
+                    <Text>{specificSource.memo}</Text>
+                  </div>
+                </Stack>
+              </Section>
+
               <Section>
                 <Stack gap={0.5}>
                   <Heading type="sectionTitle">Modules</Heading>
diff --git a/frontend/repositories/combinedDefinitionRepository.ts b/frontend/repositories/combinedDefinitionRepository.ts
index 6bcb130..ea2ac2e 100644
--- a/frontend/repositories/combinedDefinitionRepository.ts
+++ b/frontend/repositories/combinedDefinitionRepository.ts
@@ -10,6 +10,7 @@ import { get } from './httpRequest'
 type DotSourceMetadataResponse = {
   id: string
   type: 'source'
+  memo: string
   source_name: string
   modules: Array<{
     module_name: string
@@ -45,6 +46,7 @@ type CombinedDefinitionReponse = {
   dot_metadata: DotMetadataResponse[]
   sources: Array<{
     source_name: string
+    memo: string
     modules: Array<{
       module_name: string
     }>
@@ -58,6 +60,7 @@ const parseDotMetadata = (metadata: DotMetadataResponse): DotMetadata => {
         id: metadata.id,
         type: metadata.type,
         sourceName: metadata.source_name,
+        memo: metadata.memo,
         modules: metadata.modules.map((module) => ({
           moduleName: module.module_name,
         })),
@@ -99,6 +102,7 @@ const fetchDefinitionShow = async (requestPath: string): Promise<CombinedDefinit
     dotMetadata: response.dot_metadata.map((res) => parseDotMetadata(res)),
     sources: response.sources.map((source) => ({
       sourceName: source.source_name,
+      memo: source.memo,
       modules: source.modules.map((module) => ({
         moduleName: module.module_name,
       })),
diff --git a/frontend/repositories/moduleRepository.ts b/frontend/repositories/moduleRepository.ts
index 7a156a8..ea32a3d 100644
--- a/frontend/repositories/moduleRepository.ts
+++ b/frontend/repositories/moduleRepository.ts
@@ -28,6 +28,7 @@ type SpecificModuleResponse = {
   }>
   sources: Array<{
     source_name: string
+    memo: string
   }>
 }
 
@@ -39,8 +40,14 @@ export const useModule = (moduleNames: string[]) => {
       modules: response.modules.map((mod) => ({
         moduleName: mod.module_name,
       })),
-      sources: response.sources.map((source) => ({ sourceName: source.source_name })),
-      relatedDefinitions: response.related_definitions.map((definition) => ({ id: definition.id, title: definition.title })),
+      sources: response.sources.map((source) => ({
+        sourceName: source.source_name,
+        memo: source.memo,
+      })),
+      relatedDefinitions: response.related_definitions.map((definition) => ({
+        id: definition.id,
+        title: definition.title,
+      })),
     }
   })
 
diff --git a/frontend/repositories/sourceMemoRepository.ts b/frontend/repositories/sourceMemoRepository.ts
new file mode 100644
index 0000000..cf56c1a
--- /dev/null
+++ b/frontend/repositories/sourceMemoRepository.ts
@@ -0,0 +1,21 @@
+import useSWRMutation from 'swr/mutation'
+
+import { path } from '@/constants/path'
+
+import { post } from './httpRequest'
+
+const updateMemo = async (url: string, { arg }: { arg: { memo: string } }) => {
+  const { memo } = arg
+
+  await post(url, {
+    memo,
+  })
+}
+
+export const useSourceMemo = (sourceName: string) => {
+  const requestPath = path.api.sources.memo.update(sourceName)
+
+  const { trigger, isMutating } = useSWRMutation(requestPath, updateMemo)
+
+  return { trigger, isMutating }
+}
diff --git a/frontend/repositories/sourceRepository.ts b/frontend/repositories/sourceRepository.ts
index 70817e5..5bd0dc8 100644
--- a/frontend/repositories/sourceRepository.ts
+++ b/frontend/repositories/sourceRepository.ts
@@ -8,6 +8,7 @@ import { get } from './httpRequest'
 type SourcesReponse = {
   sources: Array<{
     source_name: string
+    memo: string
     modules: Array<{
       module_name: string
     }>
@@ -21,9 +22,10 @@ export const useSources = () => {
     return {
       sources: response.sources.map((source) => ({
         sourceName: source.source_name,
+        memo: source.memo,
         modules: source.modules.map((module) => ({ moduleName: module.module_name })),
       })),
-      classifiedSourcesCount: response.classified_sources_count
+      classifiedSourcesCount: response.classified_sources_count,
     }
   })
 
@@ -32,6 +34,7 @@ export const useSources = () => {
 
 type SpecificSourceResponse = {
   source_name: string
+  memo: string
   modules: Array<{
     module_name: string
   }>
@@ -55,6 +58,7 @@ export const useSource = (sourceName: string) => {
 
     return {
       sourceName: response.source_name,
+      memo: response.memo,
       modules: response.modules.map((module) => ({ moduleName: module.module_name })),
       relatedDefinitions: response.related_definitions.map((definition) => ({ id: definition.id, title: definition.title })),
       reverseDependencies: response.reverse_dependencies.map((dependency) => ({
diff --git a/lib/diver_down/web.rb b/lib/diver_down/web.rb
index 1c81c96..a922eb7 100644
--- a/lib/diver_down/web.rb
+++ b/lib/diver_down/web.rb
@@ -68,6 +68,10 @@ def call(env)
         source = Regexp.last_match[:source]
         modules = request.params['modules'] || []
         action.set_modules(source, modules)
+      in ['POST', %r{\A/api/sources/(?<source>[^/]+)/memo.json\z}]
+        source = Regexp.last_match[:source]
+        memo = request.params['memo'] || ''
+        action.set_memo(source, memo)
       in ['GET', %r{\A/api/pid\.json\z}]
         action.pid
       in ['GET', %r{\A/api/initialization_status\.json\z}]
diff --git a/lib/diver_down/web/action.rb b/lib/diver_down/web/action.rb
index afbc487..646cb60 100644
--- a/lib/diver_down/web/action.rb
+++ b/lib/diver_down/web/action.rb
@@ -33,13 +33,14 @@ def sources
         end
         # rubocop:enable Style/HashEachMethods
 
-        classified_sources_count = source_names.count { @module_store.include?(_1) }
+        classified_sources_count = source_names.count { @module_store.classified?(_1) }
 
         json(
           sources: source_names.sort.map do |source_name|
             {
               source_name:,
-              modules: @module_store.get(source_name).map do |module_name|
+              memo: @module_store.get_memo(source_name),
+              modules: @module_store.get_modules(source_name).map do |module_name|
                 { module_name: }
               end,
             }
@@ -56,7 +57,7 @@ def modules
         # rubocop:disable Style/HashEachMethods
         @store.each do |_, definition|
           definition.sources.each do |source|
-            modules = @module_store.get(source.source_name)
+            modules = @module_store.get_modules(source.source_name)
             module_set.add(modules) unless modules.empty?
           end
         end
@@ -83,7 +84,7 @@ def module(module_names)
         # rubocop:disable Style/HashEachMethods
         @store.each do |_, definition|
           definition.sources.each do |source|
-            source_module_names = @module_store.get(source.source_name)
+            source_module_names = @module_store.get_modules(source.source_name)
 
             next unless source_module_names[0..module_names.size - 1] == module_names
 
@@ -108,6 +109,7 @@ def module(module_names)
           sources: source_names.sort.map do |source_name|
             {
               source_name:,
+              memo: @module_store.get_memo(source_name),
             }
           end,
           related_definitions: related_definitions.map do |definition|
@@ -137,7 +139,7 @@ def definitions(page:, per:, title:, source:, definition_group:)
               definition_group: definition.definition_group,
               title: definition.title,
               sources_count: definition.sources.size,
-              unclassified_sources_count: definition.sources.reject { @module_store.include?(_1.source_name) }.size,
+              unclassified_sources_count: definition.sources.reject { @module_store.classified?(_1.source_name) }.size,
             }
           end,
           pagination: pagination.to_h
@@ -195,7 +197,8 @@ def combine_definitions(bit_id, compound, concentrate, only_module)
             sources: definition.sources.map do
               {
                 source_name: _1.source_name,
-                modules: @module_store.get(_1.source_name).map do |module_name|
+                memo: @module_store.get_memo(_1.source_name),
+                modules: @module_store.get_modules(_1.source_name).map do |module_name|
                   { module_name: }
                 end,
               }
@@ -246,11 +249,12 @@ def source(source_name)
                          []
                        else
                          source = DiverDown::Definition::Source.combine(*found_sources)
-                         @module_store.get(source.source_name)
+                         @module_store.get_modules(source.source_name)
                        end
 
         json(
           source_name:,
+          memo: @module_store.get_memo(source_name),
           modules: module_names.map do
             { module_name: _1 }
           end,
@@ -287,7 +291,28 @@ def set_modules(source_name, modules)
         end
 
         if found_source
-          @module_store.set(source_name, modules)
+          @module_store.set_modules(source_name, modules)
+          @module_store.flush
+
+          json({})
+        else
+          not_found
+        end
+      end
+
+      # POST /api/sources/:source_name/memo.json
+      #
+      # @param source_name [String]
+      # @param memo [String]
+      def set_memo(source_name, memo)
+        found_source = @store.any? do |_, definition|
+          definition.sources.any? do |source|
+            source.source_name == source_name
+          end
+        end
+
+        if found_source
+          @module_store.set_memo(source_name, memo)
           @module_store.flush
 
           json({})
diff --git a/lib/diver_down/web/definition_to_dot.rb b/lib/diver_down/web/definition_to_dot.rb
index d571ac2..95c1c07 100644
--- a/lib/diver_down/web/definition_to_dot.rb
+++ b/lib/diver_down/web/definition_to_dot.rb
@@ -31,7 +31,7 @@ def to_h
           private
 
           def source_to_h
-            modules = module_store.get(data.source_name).map do
+            modules = module_store.get_modules(data.source_name).map do
               {
                 module_name: _1,
               }
@@ -41,6 +41,7 @@ def source_to_h
               id:,
               type: 'source',
               source_name: data.source_name,
+              memo: module_store.get_memo(data.source_name),
               modules:,
             }
           end
@@ -185,11 +186,11 @@ def render_only_modules
         dependency_map = Hash.new { |h, k| h[k] = Hash.new { |hi, ki| hi[ki] = [] } }
 
         definition.sources.sort_by(&:source_name).each do |source|
-          source_modules = module_store.get(source.source_name)
+          source_modules = module_store.get_modules(source.source_name)
           next if source_modules.empty?
 
           source.dependencies.each do |dependency|
-            dependency_modules = module_store.get(dependency.source_name)
+            dependency_modules = module_store.get_modules(dependency.source_name)
             next if dependency_modules.empty?
 
             dependency_map[source_modules][dependency_modules].push(dependency)
@@ -268,7 +269,7 @@ def render_only_modules
 
       def render_sources
         by_modules = definition.sources.group_by do |source|
-          module_store.get(source.source_name)
+          module_store.get_modules(source.source_name)
         end
 
         # Remove duplicated prefix modules
@@ -326,8 +327,8 @@ def insert_source(source)
       def insert_dependencies(source)
         source.dependencies.each do
           attributes = {}
-          ltail = module_label(*module_store.get(source.source_name))
-          lhead = module_label(*module_store.get(_1.source_name))
+          ltail = module_label(*module_store.get_modules(source.source_name))
+          lhead = module_label(*module_store.get_modules(_1.source_name))
 
           if @compound && (ltail || lhead)
             # Rendering of dependencies between modules is done only once
diff --git a/lib/diver_down/web/module_store.rb b/lib/diver_down/web/module_store.rb
index f000673..6875ab0 100644
--- a/lib/diver_down/web/module_store.rb
+++ b/lib/diver_down/web/module_store.rb
@@ -6,6 +6,7 @@ module DiverDown
   class Web
     class ModuleStore
       BLANK_ARRAY = [].freeze
+      BLANK_MEMO = ''
       BLANK_RE = /\A\s*\z/
 
       private_constant(:BLANK_RE)
@@ -17,22 +18,42 @@ def initialize(path)
 
       # @param source_name [String]
       # @param module_names [Array<String>]
-      def set(source_name, module_names)
-        @store[source_name] = module_names.dup.reject do
+      def set_modules(source_name, module_names)
+        source = (@store[source_name] ||= {})
+
+        source[:modules] = module_names.dup.reject do
           BLANK_RE.match?(_1)
         end.freeze
       end
 
       # @param source_name [String]
       # @return [Array<Module>]
-      def get(source_name)
-        @store[source_name] || BLANK_ARRAY
+      def get_modules(source_name)
+        return BLANK_ARRAY unless @store.key?(source_name)
+
+        @store[source_name][:modules] || BLANK_ARRAY
+      end
+
+      # @param source_name [String]
+      # @param memo [String]
+      # @return [void]
+      def set_memo(source_name, memo)
+        source = (@store[source_name] ||= {})
+        source[:memo] = memo.strip
+      end
+
+      # @param source_name [String]
+      # @return [String]
+      def get_memo(source_name)
+        return BLANK_MEMO unless @store.key?(source_name)
+
+        @store[source_name][:memo] || BLANK_MEMO
       end
 
       # @param source_name [String]
       # @return [Boolean]
-      def include?(source_name)
-        get(source_name).any?
+      def classified?(source_name)
+        get_modules(source_name).any?
       end
 
       # @return [Hash]
diff --git a/spec/diver_down/web/definition_to_dot_spec.rb b/spec/diver_down/web/definition_to_dot_spec.rb
index 30d7e43..5d5da7b 100644
--- a/spec/diver_down/web/definition_to_dot_spec.rb
+++ b/spec/diver_down/web/definition_to_dot_spec.rb
@@ -48,10 +48,13 @@ def build_definition(title: 'title', sources: [])
             sources: [
               {
                 source_name: 'a.rb',
+                memo: '',
               },
             ]
           )
 
+          module_store.set_memo('a.rb', 'memo')
+
           instance = described_class.new(definition, module_store)
           expect(instance.to_s).to eq(<<~DOT)
             strict digraph "title" {
@@ -65,6 +68,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_1',
                 type: 'source',
                 source_name: 'a.rb',
+                memo: 'memo',
                 modules: [],
               },
             ]
@@ -78,6 +82,7 @@ def build_definition(title: 'title', sources: [])
             sources: [
               {
                 source_name: 'a.rb',
+                memo: '',
                 dependencies: [
                   {
                     source_name: 'b.rb',
@@ -86,6 +91,7 @@ def build_definition(title: 'title', sources: [])
               },
               {
                 source_name: 'b.rb',
+                memo: '',
               },
             ]
           )
@@ -105,11 +111,13 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_1',
                 type: 'source',
                 source_name: 'a.rb',
+                memo: '',
                 modules: [],
               }, {
                 id: 'graph_2',
                 type: 'source',
                 source_name: 'b.rb',
+                memo: '',
                 modules: [],
               }, {
                 id: 'graph_3',
@@ -136,7 +144,7 @@ def build_definition(title: 'title', sources: [])
             ]
           )
 
-          module_store.set('a.rb', ['A', 'B'])
+          module_store.set_modules('a.rb', ['A', 'B'])
 
           instance = described_class.new(definition, module_store)
 
@@ -178,6 +186,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_3',
                 type: 'source',
                 source_name: 'a.rb',
+                memo: '',
                 modules: [
                   { module_name: 'A' },
                   { module_name: 'B' },
@@ -207,9 +216,9 @@ def build_definition(title: 'title', sources: [])
             ]
           )
 
-          module_store.set('a.rb', ['A'])
-          module_store.set('b.rb', ['B'])
-          module_store.set('c.rb', ['B'])
+          module_store.set_modules('a.rb', ['A'])
+          module_store.set_modules('b.rb', ['B'])
+          module_store.set_modules('c.rb', ['B'])
 
           instance = described_class.new(definition, module_store, compound: true)
           expect(instance.to_s).to eq(<<~DOT)
@@ -244,6 +253,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_2',
                 type: 'source',
                 source_name: 'a.rb',
+                memo: '',
                 modules: [
                   { module_name: 'A' },
                 ],
@@ -259,6 +269,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_4',
                 type: 'source',
                 source_name: 'b.rb',
+                memo: '',
                 modules: [
                   { module_name: 'B' },
                 ],
@@ -266,6 +277,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_5',
                 type: 'source',
                 source_name: 'c.rb',
+                memo: '',
                 modules: [
                   { module_name: 'B' },
                 ],
@@ -320,9 +332,9 @@ def build_definition(title: 'title', sources: [])
             ]
           )
 
-          module_store.set('a.rb', ['A'])
-          module_store.set('b.rb', ['B'])
-          module_store.set('c.rb', ['B'])
+          module_store.set_modules('a.rb', ['A'])
+          module_store.set_modules('b.rb', ['B'])
+          module_store.set_modules('c.rb', ['B'])
 
           instance = described_class.new(definition, module_store, compound: true)
           expect(instance.to_s).to eq(<<~DOT)
@@ -357,6 +369,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_2',
                 type: 'source',
                 source_name: 'a.rb',
+                memo: '',
                 modules: [
                   { module_name: 'A' },
                 ],
@@ -372,6 +385,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_4',
                 type: 'source',
                 source_name: 'b.rb',
+                memo: '',
                 modules: [
                   { module_name: 'B' },
                 ],
@@ -379,6 +393,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_5',
                 type: 'source',
                 source_name: 'c.rb',
+                memo: '',
                 modules: [
                   { module_name: 'B' },
                 ],
@@ -454,11 +469,11 @@ def build_definition(title: 'title', sources: [])
             ]
           )
 
-          module_store.set('a.rb', ['A'])
-          module_store.set('b.rb', ['B'])
-          module_store.set('c.rb', ['B'])
-          module_store.set('d.rb', ['B', 'C'])
-          module_store.set('unknown.rb', ['Unknown'])
+          module_store.set_modules('a.rb', ['A'])
+          module_store.set_modules('b.rb', ['B'])
+          module_store.set_modules('c.rb', ['B'])
+          module_store.set_modules('d.rb', ['B', 'C'])
+          module_store.set_modules('unknown.rb', ['Unknown'])
 
           instance = described_class.new(definition, module_store, only_module: true)
           expect(instance.to_s).to eq(<<~DOT)
@@ -535,6 +550,7 @@ def build_definition(title: 'title', sources: [])
                 id: 'graph_1',
                 type: 'source',
                 source_name: 'a.rb',
+                memo: '',
                 modules: [],
               },
             ]
@@ -559,9 +575,9 @@ def build_definition(title: 'title', sources: [])
             ]
           )
 
-          module_store.set('b.rb', ['A'])
-          module_store.set('c.rb', ['A', 'C'])
-          module_store.set('d.rb', ['B'])
+          module_store.set_modules('b.rb', ['A'])
+          module_store.set_modules('c.rb', ['A', 'C'])
+          module_store.set_modules('d.rb', ['B'])
 
           instance = described_class.new(definition, module_store, concentrate: true)
           expect(instance.to_s).to eq(<<~DOT)
@@ -588,13 +604,13 @@ def build_definition(title: 'title', sources: [])
 
           expect(instance.metadata).to eq(
             [
-              { id: 'graph_1', type: 'source', source_name: 'a.rb', modules: [] },
+              { id: 'graph_1', type: 'source', source_name: 'a.rb', memo: '', modules: [] },
               { id: 'graph_2', type: 'module', modules: [{ module_name: 'A' }] },
-              { id: 'graph_3', type: 'source', source_name: 'b.rb', modules: [{ module_name: 'A' }] },
+              { id: 'graph_3', type: 'source', source_name: 'b.rb', memo: '', modules: [{ module_name: 'A' }] },
               { id: 'graph_4', type: 'module', modules: [{ module_name: 'A' }, { module_name: 'C' }] },
-              { id: 'graph_5', type: 'source', source_name: 'c.rb', modules: [{ module_name: 'A' }, { module_name: 'C' }] },
+              { id: 'graph_5', type: 'source', source_name: 'c.rb', memo: '', modules: [{ module_name: 'A' }, { module_name: 'C' }] },
               { id: 'graph_6', type: 'module', modules: [{ module_name: 'B' }] },
-              { id: 'graph_7', type: 'source', source_name: 'd.rb', modules: [{ module_name: 'B' }] },
+              { id: 'graph_7', type: 'source', source_name: 'd.rb', memo: '', modules: [{ module_name: 'B' }] },
             ]
           )
         end
diff --git a/spec/diver_down/web/module_store_spec.rb b/spec/diver_down/web/module_store_spec.rb
index e039885..e9918b1 100644
--- a/spec/diver_down/web/module_store_spec.rb
+++ b/spec/diver_down/web/module_store_spec.rb
@@ -9,42 +9,67 @@
       end
     end
 
-    describe '#set' do
-      it 'set modules to source' do
+    describe '#set_modules' do
+      it 'set_modules modules to source' do
         tempfile = Tempfile.new(['test', '.yaml'])
         instance = described_class.new(tempfile.path)
 
         expect {
-          instance.set('a.rb', ['A', 'B'])
+          instance.set_modules('a.rb', ['A', 'B'])
         }.to change {
-          instance.get('a.rb')
+          instance.get_modules('a.rb')
         }.from([]).to(['A', 'B'])
       end
     end
 
-    describe '#get' do
-      it 'returns blank array if source is not set' do
+    describe '#get_modules' do
+      it 'returns blank array if source is not set_modules' do
         tempfile = Tempfile.new(['test', '.yaml'])
         instance = described_class.new(tempfile.path)
 
-        expect(instance.get('a.rb')).to eq([])
+        expect(instance.get_modules('a.rb')).to eq([])
 
-        instance.set('a.rb', ['A', 'B'])
-        expect(instance.get('a.rb')).to eq(['A', 'B'])
+        instance.set_modules('a.rb', ['A', 'B'])
+        expect(instance.get_modules('a.rb')).to eq(['A', 'B'])
       end
     end
 
-    describe '#include?' do
+    describe '#set_memo' do
+      it 'sets memo' do
+        tempfile = Tempfile.new(['test', '.yaml'])
+        instance = described_class.new(tempfile.path)
+
+        expect {
+          instance.set_memo('a.rb', ' memo ')
+        }.to change {
+          instance.get_memo('a.rb')
+        }.from('').to('memo')
+      end
+    end
+
+    describe '#get_memo' do
+      it 'returns blank string if source is not set_modules' do
+        tempfile = Tempfile.new(['test', '.yaml'])
+        instance = described_class.new(tempfile.path)
+
+        expect(instance.get_memo('a.rb')).to eq('')
+
+        instance.set_memo('a.rb', 'a')
+        expect(instance.get_memo('a.rb')).to eq('a')
+      end
+    end
+
+    describe '#classified?' do
       it 'returns bool' do
         tempfile = Tempfile.new(['test', '.yaml'])
         instance = described_class.new(tempfile.path)
 
-        instance.set('a.rb', [])
-        instance.set('b.rb', ['A'])
+        instance.set_modules('a.rb', [])
+        instance.set_modules('b.rb', ['A'])
 
-        expect(instance.include?('a.rb')).to be(false)
-        expect(instance.include?('b.rb')).to be(true)
-        expect(instance.include?('c.rb')).to be(false)
+        expect(instance.classified?('a.rb')).to be(false)
+        expect(instance.classified?('b.rb')).to be(true)
+        expect(instance.classified?('c.rb')).to be(false)
       end
     end
 
@@ -52,15 +77,27 @@
       it 'writes modules to path' do
         tempfile = Tempfile.new(['test', '.yaml'])
         instance = described_class.new(tempfile.path)
-        instance.set('a.rb', ['A', 'B'])
+        instance.set_modules('a.rb', ['A', 'B'])
 
         expect {
           instance.flush
         }.to change {
-          described_class.new(tempfile.path).get('a.rb')
+          described_class.new(tempfile.path).get_modules('a.rb')
         }.from([]).to(['A', 'B'])
       end
 
+      it 'writes memo to path' do
+        tempfile = Tempfile.new(['test', '.yaml'])
+        instance = described_class.new(tempfile.path)
+        instance.set_memo('a.rb', 'memo')
+
+        expect {
+          instance.flush
+        }.to change {
+          described_class.new(tempfile.path).get_memo('a.rb')
+        }.from('').to('memo')
+      end
+
       it 'sorts by source name' do
         tempfile = Tempfile.new(['test', '.yaml'])
         instance = described_class.new(tempfile.path)
@@ -68,7 +105,7 @@
         sources = ['a.rb', 'b.rb', 'c.rb']
 
         sources.shuffle.each do |source|
-          instance.set(source, ['A'])
+          instance.set_modules(source, ['A'])
         end
 
         expect {
@@ -87,7 +124,8 @@
         sources = ['a.rb', 'b.rb', 'c.rb']
 
         sources.shuffle.each do |source|
-          instance.set(source, ['A'])
+          instance.set_modules(source, ['A'])
+          instance.set_memo(source, 'memo')
         end
 
         expect(instance.to_h.keys).to eq(sources)
diff --git a/spec/diver_down/web_spec.rb b/spec/diver_down/web_spec.rb
index 629167e..24084f0 100644
--- a/spec/diver_down/web_spec.rb
+++ b/spec/diver_down/web_spec.rb
@@ -76,7 +76,7 @@ def app
         ]
       )
       store.set(definition_1, definition_2)
-      module_store.set('a.rb', ['A'])
+      module_store.set_modules('a.rb', ['A'])
 
       get '/api/definitions.json'
 
@@ -315,7 +315,8 @@ def assert_definition_group(definition_group, expected_ids)
       )
       store.set(definition)
 
-      module_store.set('a.rb', ['A'])
+      module_store.set_modules('a.rb', ['A'])
+      module_store.set_memo('a.rb', 'memo')
 
       get '/api/sources.json'
 
@@ -324,14 +325,17 @@ def assert_definition_group(definition_group, expected_ids)
         'sources' => [
           {
             'source_name' => 'a.rb',
+            'memo' => 'memo',
             'modules' => [{ 'module_name' => 'A' }],
           },
           {
             'source_name' => 'b.rb',
+            'memo' => '',
             'modules' => [],
           },
           {
             'source_name' => 'c.rb',
+            'memo' => '',
             'modules' => [],
           },
         ],
@@ -366,8 +370,8 @@ def assert_definition_group(definition_group, expected_ids)
         ]
       )
       store.set(definition)
-      module_store.set('a.rb', ['A', 'B'])
-      module_store.set('b.rb', ['B', 'C'])
+      module_store.set_modules('a.rb', ['A', 'B'])
+      module_store.set_modules('b.rb', ['B', 'C'])
 
       get '/api/modules.json'
 
@@ -418,8 +422,9 @@ def assert_definition_group(definition_group, expected_ids)
       )
 
       ids = store.set(definition_1, definition_2)
-      module_store.set('a.rb', ['A'])
-      module_store.set('b.rb', ['A', 'B'])
+      module_store.set_modules('a.rb', ['A'])
+      module_store.set_modules('b.rb', ['A', 'B'])
+      module_store.set_memo('a.rb', 'memo')
 
       get '/api/modules/A.json'
 
@@ -433,9 +438,11 @@ def assert_definition_group(definition_group, expected_ids)
         'sources' => [
           {
             'source_name' => 'a.rb',
+            'memo' => 'memo',
           },
           {
             'source_name' => 'b.rb',
+            'memo' => '',
           },
         ],
         'related_definitions' => [
@@ -464,6 +471,7 @@ def assert_definition_group(definition_group, expected_ids)
         'sources' => [
           {
             'source_name' => 'b.rb',
+            'memo' => '',
           },
         ],
         'related_definitions' => [
@@ -486,7 +494,8 @@ def assert_definition_group(definition_group, expected_ids)
       )
 
       ids = store.set(definition)
-      module_store.set('a.rb', ['グローバル'])
+      module_store.set_modules('a.rb', ['グローバル'])
+      module_store.set_memo('a.rb', 'memo')
 
       get "/api/modules/#{CGI.escape('グローバル')}.json"
 
@@ -500,6 +509,7 @@ def assert_definition_group(definition_group, expected_ids)
         'sources' => [
           {
             'source_name' => 'a.rb',
+            'memo' => 'memo',
           },
         ],
         'related_definitions' => [
@@ -555,11 +565,29 @@ def assert_definition_group(definition_group, expected_ids)
       )
       bit_ids = store.set(definition_1, definition_2)
 
+      module_store.set_memo('a.rb', 'memo')
+
       get "/api/definitions/#{bit_ids.inject(0, &:|)}.json"
 
       expect(last_response.status).to eq(200)
       expect(last_response.headers['content-type']).to eq('application/json')
       expect(last_response.body).to include('digraph')
+
+      json = JSON.parse(last_response.body)
+      expect(json['sources']).to eq(
+        [
+          {
+            'source_name' => 'a.rb',
+            'memo' => 'memo',
+            'modules' => [],
+          },
+          {
+            'source_name' => 'b.rb',
+            'memo' => '',
+            'modules' => [],
+          },
+        ]
+      )
     end
 
     it 'returns combined definition with compound=true' do
@@ -609,9 +637,25 @@ def assert_definition_group(definition_group, expected_ids)
       store.set(definition_1)
       store.set(definition_2)
 
+      module_store.set_memo('a.rb', 'memo')
+
       get '/api/sources/a.rb.json'
 
       expect(last_response.status).to eq(200)
+
+      json = JSON.parse(last_response.body)
+      expect(json).to eq(
+        'source_name' => 'a.rb',
+        'memo' => 'memo',
+        'modules' => [],
+        'related_definitions' => [
+          {
+            'id' => 1,
+            'title' => 'title',
+          },
+        ],
+        'reverse_dependencies' => []
+      )
     end
   end
 
@@ -637,7 +681,7 @@ def assert_definition_group(definition_group, expected_ids)
 
       expect(last_response.status).to eq(200)
 
-      expect(module_store.get('a.rb')).to eq(['A', 'B'])
+      expect(module_store.get_modules('a.rb')).to eq(['A', 'B'])
     end
 
     it 'ignores blank modules' do
@@ -655,7 +699,33 @@ def assert_definition_group(definition_group, expected_ids)
 
       expect(last_response.status).to eq(200)
 
-      expect(module_store.get('a.rb')).to eq(['B'])
+      expect(module_store.get_modules('a.rb')).to eq(['B'])
+    end
+  end
+
+  describe 'POST /api/sources/:source/memo.json' do
+    it 'returns 404 if source is not found' do
+      post '/api/sources/unknown/memo.json'
+
+      expect(last_response.status).to eq(404)
+    end
+
+    it 'set memo if source is found' do
+      definition = DiverDown::Definition.new(
+        title: 'title',
+        sources: [
+          DiverDown::Definition::Source.new(
+            source_name: 'a.rb'
+          ),
+        ]
+      )
+      store.set(definition)
+
+      post '/api/sources/a.rb/memo.json', { memo: ' memo ' }
+
+      expect(last_response.status).to eq(200)
+
+      expect(module_store.get_memo('a.rb')).to eq('memo')
     end
   end
 end