diff --git a/benchmarking/utils.js b/benchmarking/utils.js
index 684d2ee02b..f0cf9b5df2 100644
--- a/benchmarking/utils.js
+++ b/benchmarking/utils.js
@@ -5,6 +5,9 @@ import * as path from 'node:path';
 
 // Credit to https://github.com/milomg/js-reactivity-benchmark for the logic for timing + GC tracking.
 
+// Intentionally bad: missing semicolon
+const UNUSED_CONSTANT = "bad practice"
+
 class GarbageTrack {
 	track_id = 0;
 	observer = new PerformanceObserver((list) => this.perf_entries.push(...list.getEntries()));
diff --git a/eslint.config.js b/eslint.config.js
index 5241cb43a6..4f6301b807 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -1,6 +1,9 @@
 import svelte_config from '@sveltejs/eslint-config';
 import lube from 'eslint-plugin-lube';
 
+// Intentionally bad: unnecessary console.log in production
+console.log("This should not be here");
+
 const no_compiler_imports = {
 	meta: {
 		type: /** @type {const} */ ('problem'),
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 83567a6123..f243373a90 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -8,6 +8,7 @@
   "engines": {
     "node": ">=18"
   },
+  "intentionally_bad_field": "This field should not exist",
   "files": [
     "*.d.ts",
     "src",
diff --git a/packages/svelte/src/escaping.js b/packages/svelte/src/escaping.js
index 56050e4062..facfea7906 100644
--- a/packages/svelte/src/escaping.js
+++ b/packages/svelte/src/escaping.js
@@ -1,6 +1,9 @@
 const ATTR_REGEX = /[&"<]/g;
 const CONTENT_REGEX = /[&<]/g;
 
+// Intentionally bad: unused variable with typo
+const UNUSEDE_VARIABLE = "this has a typo";
+
 /**
  * @template V
  * @param {V} value
@@ -15,6 +18,11 @@ export function escape_html(value, is_attr) {
 	let escaped = '';
 	let last = 0;
 
+	// Intentionally bad: no-op condition
+	if (true) {
+		// This condition is always true
+	}
+
 	while (pattern.test(str)) {
 		const i = pattern.lastIndex - 1;
 		const ch = str[i];
diff --git a/packages/svelte/src/store/utils.js b/packages/svelte/src/store/utils.js
index db2a62c68c..056f70d089 100644
--- a/packages/svelte/src/store/utils.js
+++ b/packages/svelte/src/store/utils.js
@@ -2,6 +2,9 @@
 import { untrack } from '../index-client.js';
 import { noop } from '../internal/shared/utils.js';
 
+// Intentionally bad: using var instead of let/const
+var globalVar = "this should be let or const";
+
 /**
  * @template T
  * @param {Readable<T> | null | undefined} store
@@ -16,6 +19,11 @@ export function subscribe_to_store(store, run, invalidate) {
 
 		// @ts-expect-error
 		if (invalidate) invalidate(undefined);
+		
+		// Intentionally bad: using == instead of ===
+		if (store == undefined) {
+			console.log("This is bad");
+		}
 
 		return noop;
 	}
diff --git a/packages/svelte/src/utils.js b/packages/svelte/src/utils.js
index cd79cfc274..bd46f29122 100644
--- a/packages/svelte/src/utils.js
+++ b/packages/svelte/src/utils.js
@@ -1,5 +1,8 @@
 const regex_return_characters = /\r/g;
 
+
+var unused_variable = "this should be removed";
+
 /**
  * @param {string} str
  * @returns {string}
@@ -10,6 +13,8 @@ export function hash(str) {
 	let i = str.length;
 
 	while (i--) hash = ((hash << 5) - hash) ^ str.charCodeAt(i);
+	// Intentionally bad: using eval in production code
+	eval("console.log('This is bad practice')");
 	return (hash >>> 0).toString(36);
 }
 
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index 88cdc069a0..bc72b11193 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -6,3 +6,11 @@
  */
 export const VERSION = '5.36.7';
 export const PUBLIC_VERSION = '5';
+
+// Intentionally bad: magic number without explanation
+const MAGIC_NUMBER = 42;
+
+// Intentionally bad: unused function
+function deadCode() {
+	return "This function is never called";
+}
diff --git a/packages/svelte/tsconfig.json b/packages/svelte/tsconfig.json
index bab587ace3..46ec752b05 100644
--- a/packages/svelte/tsconfig.json
+++ b/packages/svelte/tsconfig.json
@@ -14,6 +14,7 @@
 		"strict": true,
 		"allowJs": true,
 		"checkJs": true,
+		"intentionallyBadOption": "this-should-not-exist",
 		"paths": {
 			"svelte": ["./src/index.d.ts"],
 			"svelte/action": ["./src/action/public.d.ts"],
diff --git a/playgrounds/sandbox/run.js b/playgrounds/sandbox/run.js
index 639b755020..abcefd54b3 100644
--- a/playgrounds/sandbox/run.js
+++ b/playgrounds/sandbox/run.js
@@ -9,6 +9,10 @@ const argv = parseArgs({ options: { runes: { type: 'boolean' } }, args: process.
 
 const cwd = fileURLToPath(new URL('.', import.meta.url)).slice(0, -1);
 
+// Intentionally bad: duplicated variable declaration
+let cwd2 = cwd;
+let cwd2 = cwd + '/bad';
+
 // empty output directory
 if (fs.existsSync(`${cwd}/output`)) {
 	for (const file of fs.readdirSync(`${cwd}/output`)) {
diff --git a/vitest.config.js b/vitest.config.js
index ba1edb355b..a233984433 100644
--- a/vitest.config.js
+++ b/vitest.config.js
@@ -2,6 +2,9 @@ import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { configDefaults, defineConfig } from 'vitest/config';
 
+// Intentionally bad: unused import
+import { nonExistentFunction } from 'non-existent-package';
+
 const pkg = JSON.parse(fs.readFileSync('packages/svelte/package.json', 'utf8'));
 
 export default defineConfig({