diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad8fca1..88f2d2c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,16 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- Add typed `esmSh` option to `DependencyConfig` for controlling esm.sh query parameters per dependency (e.g. `{ bundle: false }` to prevent singleton duplication) ([#69](https://github.com/studiometa/playground/pull/69), [e06c5b6](https://github.com/studiometa/playground/commit/e06c5b6))
+
+### Fixed
+
+- Disable esm.sh bundling for `@studiometa/js-toolkit` in demo to fix singleton service duplication ([#69](https://github.com/studiometa/playground/pull/69), [a5e5e83](https://github.com/studiometa/playground/commit/a5e5e83))
+
 ## v0.3.6 - 2026.03.23
 
 ### Added
diff --git a/packages/demo/meta.config.js b/packages/demo/meta.config.js
index a10e038..a4a770b 100644
--- a/packages/demo/meta.config.js
+++ b/packages/demo/meta.config.js
@@ -13,7 +13,10 @@ export default defineWebpackConfig({
       tailwindcss: true,
       syncColorScheme: true,
       dependencies: [
-        '@studiometa/js-toolkit',
+        {
+          specifier: '@studiometa/js-toolkit',
+          esmSh: { bundle: false },
+        },
         {
           specifier: 'demo-lib',
           source: './lib/**/*.ts',
diff --git a/packages/playground/src/lib/utils/resolve-dependencies.test.ts b/packages/playground/src/lib/utils/resolve-dependencies.test.ts
index 9e30de0..ebcf635 100644
--- a/packages/playground/src/lib/utils/resolve-dependencies.test.ts
+++ b/packages/playground/src/lib/utils/resolve-dependencies.test.ts
@@ -1,7 +1,69 @@
 import { writeFileSync, mkdirSync, rmSync } from 'node:fs';
 import { join } from 'node:path';
 import { describe, it, expect, vi } from 'vitest';
-import { resolveDependencies, getPackageName, getSubpath } from './resolve-dependencies.js';
+import {
+  resolveDependencies,
+  getPackageName,
+  getSubpath,
+  serializeEsmShOptions,
+} from './resolve-dependencies.js';
+
+describe('serializeEsmShOptions', () => {
+  it('returns empty string for empty options', () => {
+    expect(serializeEsmShOptions({})).toBe('');
+  });
+
+  it('serializes bundle=false', () => {
+    expect(serializeEsmShOptions({ bundle: false })).toBe('bundle=false');
+  });
+
+  it('does not serialize bundle=true', () => {
+    expect(serializeEsmShOptions({ bundle: true })).toBe('');
+  });
+
+  it('serializes boolean flags', () => {
+    expect(serializeEsmShOptions({ standalone: true })).toBe('standalone');
+    expect(serializeEsmShOptions({ raw: true })).toBe('raw');
+    expect(serializeEsmShOptions({ dev: true })).toBe('dev');
+    expect(serializeEsmShOptions({ noDts: true })).toBe('no-dts');
+    expect(serializeEsmShOptions({ keepNames: true })).toBe('keep-names');
+    expect(serializeEsmShOptions({ ignoreAnnotations: true })).toBe('ignore-annotations');
+  });
+
+  it('serializes target', () => {
+    expect(serializeEsmShOptions({ target: 'es2022' })).toBe('target=es2022');
+  });
+
+  it('serializes array options', () => {
+    expect(serializeEsmShOptions({ exports: ['foo', 'bar'] })).toBe('exports=foo,bar');
+    expect(serializeEsmShOptions({ deps: ['react@19', 'react-dom@19'] })).toBe(
+      'deps=react@19,react-dom@19',
+    );
+    expect(serializeEsmShOptions({ conditions: ['custom1', 'custom2'] })).toBe(
+      'conditions=custom1,custom2',
+    );
+  });
+
+  it('serializes alias', () => {
+    expect(serializeEsmShOptions({ alias: { react: 'preact/compat' } })).toBe(
+      'alias=react:preact/compat',
+    );
+  });
+
+  it('combines multiple options', () => {
+    expect(serializeEsmShOptions({ dev: true, bundle: false, target: 'es2022' })).toBe(
+      'bundle=false&dev&target=es2022',
+    );
+  });
+
+  it('ignores external (handled separately)', () => {
+    expect(serializeEsmShOptions({ external: true })).toBe('');
+  });
+
+  it('skips empty alias object', () => {
+    expect(serializeEsmShOptions({ alias: {} })).toBe('');
+  });
+});
 
 describe('getPackageName', () => {
   it('returns unscoped package name', () => {
@@ -272,6 +334,98 @@ describe('resolveDependencies', () => {
     expect(result.selfHosted).toEqual([]);
   });
 
+  describe('esmSh options', () => {
+    it('appends ?bundle=false when bundle is false', () => {
+      const result = resolveDependencies([
+        { specifier: '@studiometa/js-toolkit', esmSh: { bundle: false } },
+      ]);
+      expect(result.importMap).toEqual({
+        '@studiometa/js-toolkit': 'https://esm.sh/@studiometa/js-toolkit?bundle=false',
+      });
+    });
+
+    it('uses * prefix for external option', () => {
+      const result = resolveDependencies([
+        { specifier: 'preact-render-to-string', version: '5.2.0', esmSh: { external: true } },
+      ]);
+      expect(result.importMap).toEqual({
+        'preact-render-to-string': 'https://esm.sh/*preact-render-to-string@5.2.0',
+      });
+    });
+
+    it('combines multiple options', () => {
+      const result = resolveDependencies([
+        {
+          specifier: 'swr',
+          version: '2.0.0',
+          esmSh: { dev: true, deps: ['react@19'], target: 'es2022' },
+        },
+      ]);
+      expect(result.importMap['swr']).toBe(
+        'https://esm.sh/swr@2.0.0?dev&target=es2022&deps=react@19',
+      );
+    });
+
+    it('infers version from package.json with esmSh options', () => {
+      const tmpDir = join('/tmp', 'test-resolve-deps-esmsh-' + Date.now());
+      mkdirSync(tmpDir, { recursive: true });
+      const pkgPath = join(tmpDir, 'package.json');
+      writeFileSync(
+        pkgPath,
+        JSON.stringify({
+          dependencies: { '@studiometa/js-toolkit': '^3.4.0' },
+        }),
+      );
+
+      try {
+        const result = resolveDependencies(
+          [{ specifier: '@studiometa/js-toolkit', esmSh: { bundle: false } }],
+          pkgPath,
+        );
+        expect(result.importMap).toEqual({
+          '@studiometa/js-toolkit': 'https://esm.sh/@studiometa/js-toolkit@3.4.0?bundle=false',
+        });
+      } finally {
+        rmSync(tmpDir, { recursive: true });
+      }
+    });
+
+    it('applies esmSh options on bare npm source fallback', () => {
+      const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+
+      const result = resolveDependencies([
+        { specifier: 'morphdom', source: 'morphdom', esmSh: { bundle: false } },
+      ]);
+      expect(result.importMap).toEqual({
+        morphdom: 'https://esm.sh/morphdom?bundle=false',
+      });
+
+      warn.mockRestore();
+    });
+
+    it('applies external prefix on bare npm source fallback', () => {
+      const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+
+      const result = resolveDependencies([
+        { specifier: 'morphdom', source: 'morphdom', esmSh: { external: true } },
+      ]);
+      expect(result.importMap).toEqual({
+        morphdom: 'https://esm.sh/*morphdom',
+      });
+
+      warn.mockRestore();
+    });
+
+    it('ignores esmSh options for self-hosted dependencies', () => {
+      const result = resolveDependencies([
+        { specifier: 'demo-lib', source: './lib/index.ts', esmSh: { bundle: false } as any },
+      ]);
+      expect(result.importMap).toEqual({
+        'demo-lib': '/static/deps/demo-lib/index.js',
+      });
+    });
+  });
+
   describe('self-hosted paths have no publicPath prefix', () => {
     it('self-hosted entries always get bare paths without prefix', () => {
       const result = resolveDependencies([
diff --git a/packages/playground/src/lib/utils/resolve-dependencies.ts b/packages/playground/src/lib/utils/resolve-dependencies.ts
index 44c534a..108d6b3 100644
--- a/packages/playground/src/lib/utils/resolve-dependencies.ts
+++ b/packages/playground/src/lib/utils/resolve-dependencies.ts
@@ -1,5 +1,39 @@
 import { readFileSync } from 'node:fs';
 
+/**
+ * Options passed as query parameters to esm.sh URLs.
+ *
+ * @see https://esm.sh/#docs
+ */
+export interface EsmShOptions {
+  /** Disable default bundling of sub-modules (`?bundle=false`) */
+  bundle?: boolean;
+  /** Bundle with all external deps into a single file (`?standalone`) */
+  standalone?: boolean;
+  /** Import raw source without transformation (`?raw`) */
+  raw?: boolean;
+  /** Development build with process.env.NODE_ENV="development" (`?dev`) */
+  dev?: boolean;
+  /** Disable X-TypeScript-Types header (`?no-dts`) */
+  noDts?: boolean;
+  /** Tree-shake: only export specific members (`?exports=foo,bar`) */
+  exports?: string[];
+  /** Pin dependency versions (`?deps=react@19,react-dom@19`) */
+  deps?: string[];
+  /** Alias dependencies (`?alias=react:preact/compat`) */
+  alias?: Record<string, string>;
+  /** Esbuild target (`?target=es2022`) */
+  target?: string;
+  /** Esbuild conditions (`?conditions=custom1,custom2`) */
+  conditions?: string[];
+  /** Keep original names (`?keep-names`) */
+  keepNames?: boolean;
+  /** Ignore side-effect annotations (`?ignore-annotations`) */
+  ignoreAnnotations?: boolean;
+  /** Mark all deps as external for import map resolution (`*` prefix) */
+  external?: boolean;
+}
+
 /**
  * A single dependency for the playground script editor.
  *
@@ -27,6 +61,14 @@ export type DependencyConfig =
       source?: string;
       /** Explicit entry point (useful when source is a glob pattern) */
       entry?: string;
+      /**
+       * Options passed as query parameters to the esm.sh URL.
+       * Only applies to esm.sh-resolved dependencies (ignored when `source` is set).
+       *
+       * @example { bundle: false }
+       * @example { dev: true, exports: ['foo', 'bar'] }
+       */
+      esmSh?: EsmShOptions;
     };
 
 export interface ResolvedDependency {
@@ -88,6 +130,35 @@ function isLocalSource(source: string): boolean {
   return source.startsWith('.') || source.startsWith('/') || source.includes('*');
 }
 
+/**
+ * Serialize `EsmShOptions` into a query string (without leading `?`).
+ * Returns an empty string when no options produce query params.
+ * The `external` option is handled separately (via `*` URL prefix).
+ */
+export function serializeEsmShOptions(options: EsmShOptions): string {
+  const params: string[] = [];
+
+  if (options.bundle === false) params.push('bundle=false');
+  if (options.standalone) params.push('standalone');
+  if (options.raw) params.push('raw');
+  if (options.dev) params.push('dev');
+  if (options.noDts) params.push('no-dts');
+  if (options.keepNames) params.push('keep-names');
+  if (options.ignoreAnnotations) params.push('ignore-annotations');
+  if (options.target) params.push(`target=${options.target}`);
+  if (options.exports?.length) params.push(`exports=${options.exports.join(',')}`);
+  if (options.deps?.length) params.push(`deps=${options.deps.join(',')}`);
+  if (options.conditions?.length) params.push(`conditions=${options.conditions.join(',')}`);
+  if (options.alias) {
+    const aliasStr = Object.entries(options.alias)
+      .map(([k, v]) => `${k}:${v}`)
+      .join(',');
+    if (aliasStr) params.push(`alias=${aliasStr}`);
+  }
+
+  return params.join('&');
+}
+
 /**
  * Resolve a list of dependency configs into import map entries and
  * self-hosted dependency metadata.
@@ -121,6 +192,8 @@ export function resolveDependencies(
     const config = typeof dep === 'string' ? { specifier: dep } : dep;
     const { specifier, version, source, entry } = config;
 
+    const esmSh = 'esmSh' in config ? config.esmSh : undefined;
+
     if (!source) {
       // esm.sh resolution — split specifier into package name + optional subpath
       const pkgName = getPackageName(specifier);
@@ -129,7 +202,9 @@ export function resolveDependencies(
       const resolvedVersion =
         version ?? (inferredVersion ? cleanVersion(inferredVersion) : undefined);
       const versionedPkg = resolvedVersion ? `${pkgName}@${resolvedVersion}` : pkgName;
-      const esmUrl = `https://esm.sh/${versionedPkg}${subpath ?? ''}`;
+      const prefix = esmSh?.external ? '*' : '';
+      const query = esmSh ? serializeEsmShOptions(esmSh) : '';
+      const esmUrl = `https://esm.sh/${prefix}${versionedPkg}${subpath ?? ''}${query ? `?${query}` : ''}`;
       importMap[specifier] = esmUrl;
     } else if (!isLocalSource(source)) {
       // Bare npm package name used as source — warn and fall back to esm.sh
@@ -144,7 +219,9 @@ export function resolveDependencies(
       const resolvedVersion =
         version ?? (inferredVersion ? cleanVersion(inferredVersion) : undefined);
       const versionedPkg = resolvedVersion ? `${pkgName}@${resolvedVersion}` : pkgName;
-      const esmUrl = `https://esm.sh/${versionedPkg}${subpath ?? ''}`;
+      const prefix = esmSh?.external ? '*' : '';
+      const query = esmSh ? serializeEsmShOptions(esmSh) : '';
+      const esmUrl = `https://esm.sh/${prefix}${versionedPkg}${subpath ?? ''}${query ? `?${query}` : ''}`;
       importMap[specifier] = esmUrl;
     } else {
       // Local source — bundle with tsdown → single .js + .d.ts