diff --git a/packages/backend/src/boot/master.ts b/packages/backend/src/boot/master.ts
index 2a23757253..b04234fd1f 100644
--- a/packages/backend/src/boot/master.ts
+++ b/packages/backend/src/boot/master.ts
@@ -31,7 +31,7 @@ function greet() {
 		console.log(themeColor(' |     |_|___ ___| |_ ___ _ _ '));
 		console.log(themeColor(' | | | | |_ -|_ -| \'_| -_| | |'));
 		console.log(themeColor(' |_|_|_|_|___|___|_,_|___|_  |'));
-		console.log(' ' + chalk.gray(v) + themeColor('                        |___|\n'.substr(v.length)));
+		console.log(' ' + chalk.gray(v) + themeColor('                        |___|\n'.substring(v.length)));
 		//#endregion
 
 		console.log(' Misskey is an open-source decentralized microblogging platform.');
diff --git a/packages/backend/src/core/chart/core.ts b/packages/backend/src/core/chart/core.ts
index d352adcc1f..5717024351 100644
--- a/packages/backend/src/core/chart/core.ts
+++ b/packages/backend/src/core/chart/core.ts
@@ -254,7 +254,7 @@ export default abstract class Chart<T extends Schema> {
 	private convertRawRecord(x: RawRecord<T>): KVs<T> {
 		const kvs = {} as Record<string, number>;
 		for (const k of Object.keys(x).filter((k) => k.startsWith(COLUMN_PREFIX)) as (keyof Columns<T>)[]) {
-			kvs[(k as string).substr(COLUMN_PREFIX.length).split(COLUMN_DELIMITER).join('.')] = x[k] as unknown as number;
+			kvs[(k as string).substring(COLUMN_PREFIX.length).split(COLUMN_DELIMITER).join('.')] = x[k] as unknown as number;
 		}
 		return kvs as KVs<T>;
 	}
diff --git a/packages/backend/src/misc/acct.ts b/packages/backend/src/misc/acct.ts
index d1a6852a95..fb3b657cf7 100644
--- a/packages/backend/src/misc/acct.ts
+++ b/packages/backend/src/misc/acct.ts
@@ -4,7 +4,7 @@ export type Acct = {
 };
 
 export function parse(acct: string): Acct {
-	if (acct.startsWith('@')) acct = acct.substr(1);
+	if (acct.startsWith('@')) acct = acct.substring(1);
 	const split = acct.split('@', 2);
 	return { username: split[0], host: split[1] ?? null };
 }
diff --git a/packages/frontend/src/components/MkDrive.file.vue b/packages/frontend/src/components/MkDrive.file.vue
index bb4361ef60..599819b3fe 100644
--- a/packages/frontend/src/components/MkDrive.file.vue
+++ b/packages/frontend/src/components/MkDrive.file.vue
@@ -25,8 +25,8 @@
 		<MkDriveFileThumbnail :class="$style.thumbnail" :file="file" fit="contain"/>
 
 		<p :class="$style.name">
-			<span>{{ file.name.lastIndexOf('.') != -1 ? file.name.substr(0, file.name.lastIndexOf('.')) : file.name }}</span>
-			<span v-if="file.name.lastIndexOf('.') != -1" style="opacity: 0.5;">{{ file.name.substr(file.name.lastIndexOf('.')) }}</span>
+			<span>{{ file.name.lastIndexOf('.') != -1 ? file.name.substring(0, file.name.lastIndexOf('.')) : file.name }}</span>
+			<span v-if="file.name.lastIndexOf('.') != -1" style="opacity: 0.5;">{{ file.name.substring(file.name.lastIndexOf('.')) }}</span>
 		</p>
 	</div>
 </div>
diff --git a/packages/frontend/src/components/MkLink.vue b/packages/frontend/src/components/MkLink.vue
index 2e4f93e848..8e61c70484 100644
--- a/packages/frontend/src/components/MkLink.vue
+++ b/packages/frontend/src/components/MkLink.vue
@@ -1,6 +1,6 @@
 <template>
 <component
-	:is="self ? 'MkA' : 'a'" ref="el" style="word-break: break-all;" class="_link" :[attr]="self ? url.substr(local.length) : url" :rel="rel" :target="target"
+	:is="self ? 'MkA' : 'a'" ref="el" style="word-break: break-all;" class="_link" :[attr]="self ? url.substring(local.length) : url" :rel="rel" :target="target"
 	:title="url"
 >
 	<slot></slot>
diff --git a/packages/frontend/src/components/MkPostForm.vue b/packages/frontend/src/components/MkPostForm.vue
index b269feb07f..462c3be6a8 100644
--- a/packages/frontend/src/components/MkPostForm.vue
+++ b/packages/frontend/src/components/MkPostForm.vue
@@ -564,7 +564,7 @@ async function onPaste(ev: ClipboardEvent) {
 				return;
 			}
 
-			quoteId = paste.substr(url.length).match(/^\/notes\/(.+?)\/?$/)[1];
+			quoteId = paste.substring(url.length).match(/^\/notes\/(.+?)\/?$/)[1];
 		});
 	}
 }
diff --git a/packages/frontend/src/components/MkReactionsViewer.reaction.vue b/packages/frontend/src/components/MkReactionsViewer.reaction.vue
index aabebb3abf..69d495d86f 100644
--- a/packages/frontend/src/components/MkReactionsViewer.reaction.vue
+++ b/packages/frontend/src/components/MkReactionsViewer.reaction.vue
@@ -6,7 +6,7 @@
 	:class="[$style.root, { [$style.reacted]: note.myReaction == reaction, [$style.canToggle]: canToggle, [$style.large]: defaultStore.state.largeNoteReactions }]"
 	@click="toggleReaction()"
 >
-	<MkReactionIcon :class="$style.icon" :reaction="reaction" :emojiUrl="note.reactionEmojis[reaction.substr(1, reaction.length - 2)]"/>
+	<MkReactionIcon :class="$style.icon" :reaction="reaction" :emojiUrl="note.reactionEmojis[reaction.substring(1, reaction.length - 1)]"/>
 	<span :class="$style.count">{{ count }}</span>
 </button>
 </template>
diff --git a/packages/frontend/src/components/MkUrlPreview.vue b/packages/frontend/src/components/MkUrlPreview.vue
index fcad5b8064..5c37f70bd9 100644
--- a/packages/frontend/src/components/MkUrlPreview.vue
+++ b/packages/frontend/src/components/MkUrlPreview.vue
@@ -32,7 +32,7 @@
 	</div>
 </template>
 <div v-else>
-	<component :is="self ? 'MkA' : 'a'" :class="[$style.link, { [$style.compact]: compact }]" :[attr]="self ? url.substr(local.length) : url" rel="nofollow noopener" :target="target" :title="url">
+	<component :is="self ? 'MkA' : 'a'" :class="[$style.link, { [$style.compact]: compact }]" :[attr]="self ? url.substring(local.length) : url" rel="nofollow noopener" :target="target" :title="url">
 		<div v-if="thumbnail" :class="$style.thumbnail" :style="`background-image: url('${thumbnail}')`">
 		</div>
 		<article :class="$style.body">
diff --git a/packages/frontend/src/components/MkUserPopup.vue b/packages/frontend/src/components/MkUserPopup.vue
index 937e0f0798..3b6e348e0b 100644
--- a/packages/frontend/src/components/MkUserPopup.vue
+++ b/packages/frontend/src/components/MkUserPopup.vue
@@ -88,7 +88,7 @@ onMounted(() => {
 		user = props.q;
 	} else {
 		const query = props.q.startsWith('@') ?
-			Acct.parse(props.q.substr(1)) :
+			Acct.parse(props.q.substring(1)) :
 			{ userId: props.q };
 
 		os.api('users/show', query).then(res => {
diff --git a/packages/frontend/src/components/global/MkCustomEmoji.vue b/packages/frontend/src/components/global/MkCustomEmoji.vue
index e8a7f17cc6..e7af472682 100644
--- a/packages/frontend/src/components/global/MkCustomEmoji.vue
+++ b/packages/frontend/src/components/global/MkCustomEmoji.vue
@@ -18,7 +18,7 @@ const props = defineProps<{
 	useOriginalSize?: boolean;
 }>();
 
-const customEmojiName = computed(() => (props.name[0] === ':' ? props.name.substr(1, props.name.length - 2) : props.name).replace('@.', ''));
+const customEmojiName = computed(() => (props.name[0] === ':' ? props.name.substring(1, props.name.length - 1) : props.name).replace('@.', ''));
 const isLocal = computed(() => !props.host && (customEmojiName.value.endsWith('@.') || !customEmojiName.value.includes('@')));
 
 const rawUrl = computed(() => {
diff --git a/packages/frontend/src/components/global/i18n.ts b/packages/frontend/src/components/global/i18n.ts
index 2708b759aa..6706d08f2f 100644
--- a/packages/frontend/src/components/global/i18n.ts
+++ b/packages/frontend/src/components/global/i18n.ts
@@ -11,13 +11,13 @@ export default function(props: { src: string; tag?: string; textTag?: string; },
 			parsed.push(str);
 			break;
 		} else {
-			if (nextBracketOpen > 0) parsed.push(str.substr(0, nextBracketOpen));
+			if (nextBracketOpen > 0) parsed.push(str.substring(0, nextBracketOpen));
 			parsed.push({
 				arg: str.substring(nextBracketOpen + 1, nextBracketClose),
 			});
 		}
 
-		str = str.substr(nextBracketClose + 1);
+		str = str.substring(nextBracketClose + 1);
 	}
 
 	return h(props.tag ?? 'span', parsed.map(x => typeof x === 'string' ? (props.textTag ? h(props.textTag, x) : x) : slots[x.arg]()));
diff --git a/packages/frontend/src/pages/admin/overview.queue.vue b/packages/frontend/src/pages/admin/overview.queue.vue
index b08757aeb8..7d8d468512 100644
--- a/packages/frontend/src/pages/admin/overview.queue.vue
+++ b/packages/frontend/src/pages/admin/overview.queue.vue
@@ -85,7 +85,7 @@ onMounted(() => {
 	connection.on('stats', onStats);
 	connection.on('statsLog', onStatsLog);
 	connection.send('requestLog', {
-		id: Math.random().toString().substr(2, 8),
+		id: Math.random().toString().substring(2, 10),
 		length: 100,
 	});
 });
diff --git a/packages/frontend/src/pages/admin/overview.vue b/packages/frontend/src/pages/admin/overview.vue
index 838c197f05..41a6d4f5b7 100644
--- a/packages/frontend/src/pages/admin/overview.vue
+++ b/packages/frontend/src/pages/admin/overview.vue
@@ -156,7 +156,7 @@ onMounted(async () => {
 
 	nextTick(() => {
 		queueStatsConnection.send('requestLog', {
-			id: Math.random().toString().substr(2, 8),
+			id: Math.random().toString().substring(2, 10),
 			length: 100,
 		});
 	});
diff --git a/packages/frontend/src/pages/admin/queue.chart.vue b/packages/frontend/src/pages/admin/queue.chart.vue
index 8e6856fddd..83ca9639e7 100644
--- a/packages/frontend/src/pages/admin/queue.chart.vue
+++ b/packages/frontend/src/pages/admin/queue.chart.vue
@@ -106,7 +106,7 @@ onMounted(() => {
 	connection.on('stats', onStats);
 	connection.on('statsLog', onStatsLog);
 	connection.send('requestLog', {
-		id: Math.random().toString().substr(2, 8),
+		id: Math.random().toString().substring(2, 10),
 		length: 200,
 	});
 });
diff --git a/packages/frontend/src/scripts/autocomplete.ts b/packages/frontend/src/scripts/autocomplete.ts
index 1bae3790f5..564573ae8a 100644
--- a/packages/frontend/src/scripts/autocomplete.ts
+++ b/packages/frontend/src/scripts/autocomplete.ts
@@ -65,7 +65,7 @@ export class Autocomplete {
 	 */
 	private onInput() {
 		const caretPos = this.textarea.selectionStart;
-		const text = this.text.substr(0, caretPos).split('\n').pop()!;
+		const text = this.text.substring(0, caretPos).split('\n').pop()!;
 
 		const mentionIndex = text.lastIndexOf('@');
 		const hashtagIndex = text.lastIndexOf('#');
@@ -91,7 +91,7 @@ export class Autocomplete {
 		let opened = false;
 
 		if (isMention) {
-			const username = text.substr(mentionIndex + 1);
+			const username = text.substring(mentionIndex + 1);
 			if (username !== '' && username.match(/^[a-zA-Z0-9_]+$/)) {
 				this.open('user', username);
 				opened = true;
@@ -102,7 +102,7 @@ export class Autocomplete {
 		}
 
 		if (isHashtag && !opened) {
-			const hashtag = text.substr(hashtagIndex + 1);
+			const hashtag = text.substring(hashtagIndex + 1);
 			if (!hashtag.includes(' ')) {
 				this.open('hashtag', hashtag);
 				opened = true;
@@ -110,7 +110,7 @@ export class Autocomplete {
 		}
 
 		if (isEmoji && !opened) {
-			const emoji = text.substr(emojiIndex + 1);
+			const emoji = text.substring(emojiIndex + 1);
 			if (!emoji.includes(' ')) {
 				this.open('emoji', emoji);
 				opened = true;
@@ -118,7 +118,7 @@ export class Autocomplete {
 		}
 
 		if (isMfmTag && !opened) {
-			const mfmTag = text.substr(mfmTagIndex + 1);
+			const mfmTag = text.substring(mfmTagIndex + 1);
 			if (!mfmTag.includes(' ')) {
 				this.open('mfmTag', mfmTag.replace('[', ''));
 				opened = true;
@@ -208,9 +208,9 @@ export class Autocomplete {
 		if (type === 'user') {
 			const source = this.text;
 
-			const before = source.substr(0, caret);
+			const before = source.substring(0, caret);
 			const trimmedBefore = before.substring(0, before.lastIndexOf('@'));
-			const after = source.substr(caret);
+			const after = source.substring(caret);
 
 			const acct = value.host === null ? value.username : `${value.username}@${toASCII(value.host)}`;
 
@@ -226,9 +226,9 @@ export class Autocomplete {
 		} else if (type === 'hashtag') {
 			const source = this.text;
 
-			const before = source.substr(0, caret);
+			const before = source.substring(0, caret);
 			const trimmedBefore = before.substring(0, before.lastIndexOf('#'));
-			const after = source.substr(caret);
+			const after = source.substring(caret);
 
 			// 挿入
 			this.text = `${trimmedBefore}#${value} ${after}`;
@@ -242,9 +242,9 @@ export class Autocomplete {
 		} else if (type === 'emoji') {
 			const source = this.text;
 
-			const before = source.substr(0, caret);
+			const before = source.substring(0, caret);
 			const trimmedBefore = before.substring(0, before.lastIndexOf(':'));
-			const after = source.substr(caret);
+			const after = source.substring(caret);
 
 			// 挿入
 			this.text = trimmedBefore + value + after;
@@ -258,9 +258,9 @@ export class Autocomplete {
 		} else if (type === 'mfmTag') {
 			const source = this.text;
 
-			const before = source.substr(0, caret);
+			const before = source.substring(0, caret);
 			const trimmedBefore = before.substring(0, before.lastIndexOf('$'));
-			const after = source.substr(caret);
+			const after = source.substring(caret);
 
 			// 挿入
 			this.text = `${trimmedBefore}$[${value} ]${after}`;
diff --git a/packages/frontend/src/scripts/gen-search-query.ts b/packages/frontend/src/scripts/gen-search-query.ts
index da7d622632..956e0f35d0 100644
--- a/packages/frontend/src/scripts/gen-search-query.ts
+++ b/packages/frontend/src/scripts/gen-search-query.ts
@@ -5,7 +5,7 @@ export async function genSearchQuery(v: any, q: string) {
 	let host: string;
 	let userId: string;
 	if (q.split(' ').some(x => x.startsWith('@'))) {
-		for (const at of q.split(' ').filter(x => x.startsWith('@')).map(x => x.substr(1))) {
+		for (const at of q.split(' ').filter(x => x.startsWith('@')).map(x => x.substring(1))) {
 			if (at.includes('.')) {
 				if (at === localHost || at === '.') {
 					host = null;
diff --git a/packages/frontend/src/scripts/lookup.ts b/packages/frontend/src/scripts/lookup.ts
index a55868368e..3f357a3c92 100644
--- a/packages/frontend/src/scripts/lookup.ts
+++ b/packages/frontend/src/scripts/lookup.ts
@@ -18,7 +18,7 @@ export async function lookup(router?: Router) {
 	}
 
 	if (query.startsWith('#')) {
-		_router.push(`/tags/${encodeURIComponent(query.substr(1))}`);
+		_router.push(`/tags/${encodeURIComponent(query.substring(1))}`);
 		return;
 	}
 
diff --git a/packages/frontend/src/scripts/theme-editor.ts b/packages/frontend/src/scripts/theme-editor.ts
index 944875ff15..001d87381c 100644
--- a/packages/frontend/src/scripts/theme-editor.ts
+++ b/packages/frontend/src/scripts/theme-editor.ts
@@ -35,7 +35,7 @@ export const fromThemeString = (str?: string) : ThemeValue => {
 	} else if (str.startsWith('"')) {
 		return {
 			type: 'css',
-			value: str.substr(1).trim(),
+			value: str.substring(1).trim(),
 		};
 	} else {
 		return str;
diff --git a/packages/frontend/src/scripts/theme.ts b/packages/frontend/src/scripts/theme.ts
index f2e8253565..bc61256cac 100644
--- a/packages/frontend/src/scripts/theme.ts
+++ b/packages/frontend/src/scripts/theme.ts
@@ -98,7 +98,7 @@ function compile(theme: Theme): Record<string, string> {
 	function getColor(val: string): tinycolor.Instance {
 		// ref (prop)
 		if (val[0] === '@') {
-			return getColor(theme.props[val.substr(1)]);
+			return getColor(theme.props[val.substring(1)]);
 		}
 
 		// ref (const)
@@ -109,7 +109,7 @@ function compile(theme: Theme): Record<string, string> {
 		// func
 		else if (val[0] === ':') {
 			const parts = val.split('<');
-			const func = parts.shift().substr(1);
+			const func = parts.shift().substring(1);
 			const arg = parseFloat(parts.shift());
 			const color = getColor(parts.join('<'));
 
diff --git a/packages/frontend/src/widgets/WidgetJobQueue.vue b/packages/frontend/src/widgets/WidgetJobQueue.vue
index 3c8ffdb55a..36706c37e4 100644
--- a/packages/frontend/src/widgets/WidgetJobQueue.vue
+++ b/packages/frontend/src/widgets/WidgetJobQueue.vue
@@ -124,7 +124,7 @@ connection.on('stats', onStats);
 connection.on('statsLog', onStatsLog);
 
 connection.send('requestLog', {
-	id: Math.random().toString().substr(2, 8),
+	id: Math.random().toString().substring(2, 10),
 	length: 1,
 });
 
diff --git a/packages/frontend/src/widgets/server-metric/cpu-mem.vue b/packages/frontend/src/widgets/server-metric/cpu-mem.vue
index 80a8e427e1..c178ba5171 100644
--- a/packages/frontend/src/widgets/server-metric/cpu-mem.vue
+++ b/packages/frontend/src/widgets/server-metric/cpu-mem.vue
@@ -100,7 +100,7 @@ onMounted(() => {
 	props.connection.on('stats', onStats);
 	props.connection.on('statsLog', onStatsLog);
 	props.connection.send('requestLog', {
-		id: Math.random().toString().substr(2, 8),
+		id: Math.random().toString().substring(2, 10),
 	});
 });
 
diff --git a/packages/frontend/src/widgets/server-metric/net.vue b/packages/frontend/src/widgets/server-metric/net.vue
index ab8b0fe471..5a9134078d 100644
--- a/packages/frontend/src/widgets/server-metric/net.vue
+++ b/packages/frontend/src/widgets/server-metric/net.vue
@@ -70,7 +70,7 @@ onMounted(() => {
 	props.connection.on('stats', onStats);
 	props.connection.on('statsLog', onStatsLog);
 	props.connection.send('requestLog', {
-		id: Math.random().toString().substr(2, 8),
+		id: Math.random().toString().substring(2, 10),
 	});
 });
 
diff --git a/packages/misskey-js/src/acct.ts b/packages/misskey-js/src/acct.ts
index c32cee86c9..b25bc564ea 100644
--- a/packages/misskey-js/src/acct.ts
+++ b/packages/misskey-js/src/acct.ts
@@ -4,7 +4,7 @@ export type Acct = {
 };
 
 export function parse(acct: string): Acct {
-	if (acct.startsWith('@')) acct = acct.substr(1);
+	if (acct.startsWith('@')) acct = acct.substring(1);
 	const split = acct.split('@', 2);
 	return { username: split[0], host: split[1] || null };
 }