diff --git a/packages/core/src/ide/ide-installer.ts b/packages/core/src/ide/ide-installer.ts
index 52dcb6fb4ce..cefb1b05039 100644
--- a/packages/core/src/ide/ide-installer.ts
+++ b/packages/core/src/ide/ide-installer.ts
@@ -136,8 +136,8 @@ class VsCodeInstaller implements IdeInstaller {
         ['--install-extension', vsixPath, '--force'],
         {
           stdio: 'pipe',
-          shell: os.platform() === 'win32' && commandPath.endsWith('.cmd')
-        }
+          shell: os.platform() === 'win32' && commandPath.endsWith('.cmd'),
+        },
       );
       return {
         success: true,
diff --git a/packages/core/src/tools/edit.ts b/packages/core/src/tools/edit.ts
index 333232035e5..f8e1c36ec54 100644
--- a/packages/core/src/tools/edit.ts
+++ b/packages/core/src/tools/edit.ts
@@ -22,7 +22,7 @@ import { ToolErrorType } from './tool-error.js';
 import { Type } from '@google/genai';
 import { SchemaValidator } from '../utils/schemaValidator.js';
 import { makeRelative, shortenPath } from '../utils/paths.js';
-import { isNodeError } from '../utils/errors.js';
+import { getErrorMessage, isNodeError } from '../utils/errors.js';
 import { Config, ApprovalMode } from '../config/config.js';
 import { ensureCorrectEdit } from '../utils/editCorrector.js';
 import { DEFAULT_DIFF_OPTIONS, getDiffStat } from './diffOptions.js';
@@ -229,8 +229,8 @@ class EditToolInvocation implements ToolInvocation<EditToolParams, ToolResult> {
     let editData: CalculatedEdit;
     try {
       editData = await this.calculateEdit(this.params, abortSignal);
-    } catch (error) {
-      const errorMsg = error instanceof Error ? error.message : String(error);
+    } catch (error: unknown) {
+      const errorMsg = getErrorMessage(error);
       console.log(`Error preparing edit: ${errorMsg}`);
       return false;
     }
@@ -316,8 +316,8 @@ class EditToolInvocation implements ToolInvocation<EditToolParams, ToolResult> {
     let editData: CalculatedEdit;
     try {
       editData = await this.calculateEdit(this.params, signal);
-    } catch (error) {
-      const errorMsg = error instanceof Error ? error.message : String(error);
+    } catch (error: unknown) {
+      const errorMsg = getErrorMessage(error);
       return {
         llmContent: `Error preparing edit: ${errorMsg}`,
         returnDisplay: `Error preparing edit: ${errorMsg}`,
@@ -390,8 +390,8 @@ class EditToolInvocation implements ToolInvocation<EditToolParams, ToolResult> {
         llmContent: llmSuccessMessageParts.join(' '),
         returnDisplay: displayResult,
       };
-    } catch (error) {
-      const errorMsg = error instanceof Error ? error.message : String(error);
+    } catch (error: unknown) {
+      const errorMsg = getErrorMessage(error);
       return {
         llmContent: `Error executing edit: ${errorMsg}`,
         returnDisplay: `Error writing file: ${errorMsg}`,
diff --git a/packages/core/src/utils/errors.test.ts b/packages/core/src/utils/errors.test.ts
index ec42a3f954f..59cc5a37f53 100644
--- a/packages/core/src/utils/errors.test.ts
+++ b/packages/core/src/utils/errors.test.ts
@@ -1,10 +1,17 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 import { describe, it, expect } from 'vitest';
+
 import {
   toFriendlyError,
   BadRequestError,
   UnauthorizedError,
   ForbiddenError,
-} from './errors';
+} from './errors.js';
 
 describe('toFriendlyError', () => {
   it('should return the original error if it is not an object', () => {
diff --git a/packages/core/src/utils/fetch.test.ts b/packages/core/src/utils/fetch.test.ts
index 02d7c6f2df4..d00012cc1a8 100644
--- a/packages/core/src/utils/fetch.test.ts
+++ b/packages/core/src/utils/fetch.test.ts
@@ -91,7 +91,8 @@ describe('fetchWithTimeout', () => {
   it('should throw FetchError with ETIMEDOUT code when request times out', async () => {
     // Mock fetch to simulate timeout behavior
     (fetch as unknown as ReturnType<typeof vi.fn>).mockImplementation(
-      (url: string, options: { signal: AbortSignal }) => new Promise((_, reject) => {
+      (url: string, options: { signal: AbortSignal }) =>
+        new Promise((_, reject) => {
           if (options.signal.aborted) {
             const error = new Error('The operation was aborted');
             (error as any).code = 'ABORT_ERR';