diff --git a/scripts/hooks/post-edit-format.js b/scripts/hooks/post-edit-format.js
index 2f1d0334b..e2c77188d 100644
--- a/scripts/hooks/post-edit-format.js
+++ b/scripts/hooks/post-edit-format.js
@@ -15,6 +15,29 @@ const fs = require('fs');
 const path = require('path');
 
 const MAX_STDIN = 1024 * 1024; // 1MB limit
+const BIOME_CONFIGS = ['biome.json', 'biome.jsonc'];
+const PRETTIER_CONFIGS = [
+  '.prettierrc',
+  '.prettierrc.json',
+  '.prettierrc.json5',
+  '.prettierrc.js',
+  '.prettierrc.cjs',
+  '.prettierrc.mjs',
+  '.prettierrc.ts',
+  '.prettierrc.cts',
+  '.prettierrc.mts',
+  '.prettierrc.yml',
+  '.prettierrc.yaml',
+  '.prettierrc.toml',
+  'prettier.config.js',
+  'prettier.config.cjs',
+  'prettier.config.mjs',
+  'prettier.config.ts',
+  'prettier.config.cts',
+  'prettier.config.mts',
+];
+const PROJECT_ROOT_MARKERS = ['package.json', ...BIOME_CONFIGS, ...PRETTIER_CONFIGS];
+
 let data = '';
 process.stdin.setEncoding('utf8');
 
@@ -27,33 +50,26 @@ process.stdin.on('data', chunk => {
 
 function findProjectRoot(startDir) {
   let dir = startDir;
-  while (dir !== path.dirname(dir)) {
-    if (fs.existsSync(path.join(dir, 'package.json'))) return dir;
-    dir = path.dirname(dir);
+
+  while (true) {
+    if (PROJECT_ROOT_MARKERS.some(marker => fs.existsSync(path.join(dir, marker)))) {
+      return dir;
+    }
+
+    const parentDir = path.dirname(dir);
+    if (parentDir === dir) break;
+    dir = parentDir;
   }
+
   return startDir;
 }
 
 function detectFormatter(projectRoot) {
-  const biomeConfigs = ['biome.json', 'biome.jsonc'];
-  for (const cfg of biomeConfigs) {
+  for (const cfg of BIOME_CONFIGS) {
     if (fs.existsSync(path.join(projectRoot, cfg))) return 'biome';
   }
 
-  const prettierConfigs = [
-    '.prettierrc',
-    '.prettierrc.json',
-    '.prettierrc.js',
-    '.prettierrc.cjs',
-    '.prettierrc.mjs',
-    '.prettierrc.yml',
-    '.prettierrc.yaml',
-    '.prettierrc.toml',
-    'prettier.config.js',
-    'prettier.config.cjs',
-    'prettier.config.mjs',
-  ];
-  for (const cfg of prettierConfigs) {
+  for (const cfg of PRETTIER_CONFIGS) {
     if (fs.existsSync(path.join(projectRoot, cfg))) return 'prettier';
   }
 
diff --git a/tests/hooks/hooks.test.js b/tests/hooks/hooks.test.js
index 2c8732042..31d486d35 100644
--- a/tests/hooks/hooks.test.js
+++ b/tests/hooks/hooks.test.js
@@ -701,6 +701,49 @@ async function runTests() {
     assert.ok(result.stdout.includes('tool_input'), 'Should pass through original data');
   })) passed++; else failed++;
 
+  if (await asyncTest('finds formatter config in parent dirs even without package.json', async () => {
+    const testDir = createTestDir();
+    const repoRoot = path.join(testDir, 'config-only-repo');
+    const nestedDir = path.join(repoRoot, 'src', 'nested');
+    const targetFile = path.join(nestedDir, 'file.ts');
+    const binDir = path.join(testDir, 'bin');
+    const logFile = path.join(testDir, 'npx-log.json');
+
+    fs.mkdirSync(nestedDir, { recursive: true });
+    fs.mkdirSync(binDir, { recursive: true });
+    fs.writeFileSync(path.join(repoRoot, 'biome.json'), '{}\n');
+    fs.writeFileSync(targetFile, 'const value = 1;\n');
+    fs.writeFileSync(
+      path.join(binDir, 'npx'),
+      `#!/usr/bin/env node\nconst fs = require('fs');\nfs.writeFileSync(${JSON.stringify(logFile)}, JSON.stringify({ cwd: process.cwd(), args: process.argv.slice(2) }));\n`,
+      { mode: 0o755 }
+    );
+
+    try {
+      const stdinJson = JSON.stringify({ tool_input: { file_path: targetFile } });
+      const result = await runScript(path.join(scriptsDir, 'post-edit-format.js'), stdinJson, {
+        PATH: `${binDir}${path.delimiter}${process.env.PATH || ''}`,
+      });
+
+      assert.strictEqual(result.code, 0, 'Should exit 0 for config-only repos');
+      assert.ok(fs.existsSync(logFile), 'Should invoke formatter when parent biome config exists');
+
+      const invocation = JSON.parse(fs.readFileSync(logFile, 'utf8'));
+      assert.strictEqual(
+        fs.realpathSync(invocation.cwd),
+        fs.realpathSync(repoRoot),
+        'Should run formatter from discovered repo root'
+      );
+      assert.deepStrictEqual(
+        invocation.args,
+        ['@biomejs/biome', 'format', '--write', targetFile],
+        'Should invoke biome formatter for config-only repo'
+      );
+    } finally {
+      cleanupTestDir(testDir);
+    }
+  })) passed++; else failed++;
+
   // post-edit-typecheck.js tests
   console.log('\npost-edit-typecheck.js:');