diff --git a/packages/rstack/src/fmt/plugins.ts b/packages/rstack/src/fmt/plugins.ts
index 17ebcc24..fea4734b 100644
--- a/packages/rstack/src/fmt/plugins.ts
+++ b/packages/rstack/src/fmt/plugins.ts
@@ -1,11 +1,14 @@
-import { isAbsolute, join, resolve as resolvePath } from 'node:path';
-import { pathToFileURL } from 'node:url';
+import { readFile, realpath } from 'node:fs/promises';
+import { isAbsolute, join, relative, resolve as resolvePath, sep } from 'node:path';
+import { fileURLToPath, pathToFileURL } from 'node:url';
 import { moduleResolve } from 'import-meta-resolve';
 import type { Options as PrettierOptions } from 'prettier';
+import { toPosixPath } from './pathHelpers.ts';
 import type { FmtPluginSpecifier, ResolvedFmtOptions } from './types.ts';
 
 type FmtPlugin = NonNullable<PrettierOptions['plugins']>[number];
 type FmtPluginResolver = (options: ResolvedFmtOptions) => ResolvedFmtOptions;
+type FingerprintResolver = (plugin: FmtPluginSpecifier) => Promise<string | undefined>;
 
 const resolveModuleUrl = (specifier: string, parentUrl: URL): string =>
   moduleResolve(specifier, parentUrl).href;
@@ -13,6 +16,81 @@ const resolveModuleUrl = (specifier: string, parentUrl: URL): string =>
 const isFmtPluginSpecifier = (plugin: FmtPlugin): plugin is FmtPluginSpecifier =>
   typeof plugin === 'string' || plugin instanceof URL;
 
+const getPackageRoot = (entryPath: string): string | undefined => {
+  const marker = `${sep}node_modules${sep}`;
+  const index = entryPath.lastIndexOf(marker);
+  if (index === -1) {
+    return undefined;
+  }
+  const start = index + marker.length;
+
+  let end = entryPath.indexOf(sep, start);
+  if (end === -1) {
+    return undefined;
+  }
+  if (entryPath[start] === '@') {
+    end = entryPath.indexOf(sep, end + 1);
+    if (end === -1) {
+      return undefined;
+    }
+  }
+
+  return entryPath.slice(0, end);
+};
+
+const fingerprintPlugin = async (pluginUrl: string): Promise<string | undefined> => {
+  try {
+    const url = new URL(pluginUrl);
+    if (url.protocol !== 'file:') {
+      return undefined;
+    }
+
+    // Resolving symlinks keeps workspace and other local plugins out of the
+    // package-version fast path when their implementation can change in place.
+    const entryPath = await realpath(fileURLToPath(url));
+    const packageRoot = getPackageRoot(entryPath);
+    if (packageRoot === undefined) {
+      return undefined;
+    }
+
+    const pkg: unknown = JSON.parse(await readFile(join(packageRoot, 'package.json'), 'utf8'));
+    if (
+      typeof pkg !== 'object' ||
+      pkg === null ||
+      !('name' in pkg) ||
+      typeof pkg.name !== 'string' ||
+      !('version' in pkg) ||
+      typeof pkg.version !== 'string'
+    ) {
+      return undefined;
+    }
+
+    return JSON.stringify([
+      'package',
+      pkg.name,
+      pkg.version,
+      toPosixPath(relative(packageRoot, entryPath)),
+    ]);
+  } catch {
+    return undefined;
+  }
+};
+
+/** Creates a memoized identity resolver for installed package plugins. */
+const createFingerprintResolver = (): FingerprintResolver => {
+  const cache = new Map<string, Promise<string | undefined>>();
+
+  return (plugin) => {
+    const pluginUrl = plugin instanceof URL ? plugin.href : plugin;
+    let fingerprint = cache.get(pluginUrl);
+    if (fingerprint === undefined) {
+      fingerprint = fingerprintPlugin(pluginUrl);
+      cache.set(pluginUrl, fingerprint);
+    }
+    return fingerprint;
+  };
+};
+
 /** Creates a project-root resolver for plugins in final per-file options. */
 const createFmtPluginResolver = (rootPath: string): FmtPluginResolver => {
   const parentUrl = pathToFileURL(join(rootPath, 'index.js'));
@@ -65,5 +143,5 @@ const createFmtPluginResolver = (rootPath: string): FmtPluginResolver => {
   };
 };
 
-export { createFmtPluginResolver };
-export type { FmtPluginResolver };
+export { createFingerprintResolver, createFmtPluginResolver };
+export type { FingerprintResolver, FmtPluginResolver };
diff --git a/packages/rstack/tests/fmt/plugins.test.ts b/packages/rstack/tests/fmt/plugins.test.ts
index cac6da5b..7d2a34f7 100644
--- a/packages/rstack/tests/fmt/plugins.test.ts
+++ b/packages/rstack/tests/fmt/plugins.test.ts
@@ -1,6 +1,6 @@
 import { pathToFileURL } from 'node:url';
 import { expect, test } from 'rstack/test';
-import { createFmtPluginResolver } from '../../src/fmt/plugins.ts';
+import { createFingerprintResolver, createFmtPluginResolver } from '../../src/fmt/plugins.ts';
 import { withTempProject, writeProjectFile } from './helpers.ts';
 
 test('resolves plugin specifiers from the config root', async () => {
@@ -60,3 +60,57 @@ test('rejects imported plugin objects', () => {
     'Prettier plugin objects are not supported. Use a package name, path, or URL instead.',
   );
 });
+
+test('fingerprints installed package plugins once', async () => {
+  await withTempProject(async (rootPath) => {
+    const entry = writeProjectFile(rootPath, 'node_modules/prettier-plugin-fixture/dist/index.mjs');
+    const packageJsonPath = 'node_modules/prettier-plugin-fixture/package.json';
+    writeProjectFile(
+      rootPath,
+      packageJsonPath,
+      JSON.stringify({ name: 'prettier-plugin-fixture', version: '1.2.3' }),
+    );
+
+    const resolveFingerprint = createFingerprintResolver();
+    const pluginUrl = pathToFileURL(entry);
+    const fingerprint = JSON.stringify([
+      'package',
+      'prettier-plugin-fixture',
+      '1.2.3',
+      'dist/index.mjs',
+    ]);
+
+    await expect(resolveFingerprint(pluginUrl)).resolves.toBe(fingerprint);
+
+    writeProjectFile(
+      rootPath,
+      packageJsonPath,
+      JSON.stringify({ name: 'prettier-plugin-fixture', version: '2.0.0' }),
+    );
+    await expect(resolveFingerprint(pluginUrl)).resolves.toBe(fingerprint);
+  });
+});
+
+test('skips plugins without stable package metadata', async () => {
+  await withTempProject(async (rootPath) => {
+    const localPlugin = writeProjectFile(rootPath, 'plugins/local.mjs');
+    const unversionedPlugin = writeProjectFile(
+      rootPath,
+      'node_modules/prettier-plugin-fixture/index.mjs',
+    );
+    writeProjectFile(
+      rootPath,
+      'node_modules/prettier-plugin-fixture/package.json',
+      JSON.stringify({ name: 'prettier-plugin-fixture' }),
+    );
+
+    const resolveFingerprint = createFingerprintResolver();
+    await expect(
+      Promise.all([
+        resolveFingerprint(pathToFileURL(localPlugin)),
+        resolveFingerprint(pathToFileURL(unversionedPlugin)),
+        resolveFingerprint('data:text/javascript,export default {}'),
+      ]),
+    ).resolves.toEqual([undefined, undefined, undefined]);
+  });
+});