diff --git a/.talismanrc b/.talismanrc
index df8a173..b7172be 100644
--- a/.talismanrc
+++ b/.talismanrc
@@ -3,7 +3,7 @@ fileignoreconfig:
   ignore_detectors:
     - filecontent
 - filename: package-lock.json
-  checksum: af3bffd9f46b71daf5b8dd0b3eace75dfd367e359b11503259dc00a8c7105bf0
+  checksum: 59653dc17458f6bddffb6178bfb8f8191ad4715f41a788082a11d3b08e966b4c
 - filename: .husky/pre-commit
   checksum: 5baabd7d2c391648163f9371f0e5e9484f8fb90fa2284cfc378732ec3192c193
 - filename: test/request.spec.ts
@@ -14,4 +14,6 @@ fileignoreconfig:
   checksum: 08ccd6342b3adbeb7b85309a034b4df4b2ad905a0cc2a3778ab483b61ba41b9e
 - filename: test/retryPolicy/delivery-sdk-handlers.spec.ts
   checksum: 6d22d7482aa6dccba5554ae497e5b0c3572357a5cead6f4822ee4428edc12207
+- filename: test/contentstack-core.spec.ts
+  checksum: 2d1e0f63ad8ea37890de2aa6c7e394c83488888f4a40ad7a71eeba2290b95924
 version: ""
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index cee9d05..41bafda 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,20 @@
 ## Change log
 
+### Version: 1.3.8
+#### Date: Jan-12-2026
+ - Fix: Add .js extensions to relative imports in ESM build for proper module resolution
+ - Fix: Change lodash import from named import to default import for ESM compatibility with CommonJS modules
+
+### Version: 1.3.7
+#### Date: Jan-12-2026
+ - Fix: Improve error messages
+
+
+### Version: 1.3.8
+#### Date: Jan-15-2026
+ - Fix: Add .js extensions to relative imports in ESM build for proper module resolution
+ - Fix: Change lodash import from named import to default import for ESM compatibility with CommonJS modules
+
 ### Version: 1.3.7
 #### Date: Jan-12-2026
  - Fix: Improve error messages
diff --git a/README.md b/README.md
index 74d78d1..34dc0f4 100644
--- a/README.md
+++ b/README.md
@@ -1,46 +1,129 @@
+# @contentstack/core
+
 [![Contentstack](https://www.contentstack.com/docs/static/images/contentstack.png)](https://www.contentstack.com/)
-## TypeScript Core SDK for Contentstack
+
+TypeScript Core SDK for Contentstack - A foundational library providing core modules and utilities for Contentstack TypeScript SDKs.
+
+## About Contentstack
 
 Contentstack is a headless CMS with an API-first approach. It is a CMS that developers can use to build powerful cross-platform applications in their favorite languages. Build your application frontend, and Contentstack will take care of the rest. [Read More](https://www.contentstack.com/).
 
-### Prerequisite
+## Description
 
-You need Node.js version 4.4.7 or later installed to use the Contentstack TS Core SDK.
+This package contains core modules and utilities used by the [Contentstack TypeScript Delivery SDK](https://github.com/contentstack/contentstack-javascript/). It provides essential functionality including HTTP client configuration, error handling, request management, parameter serialization, and retry policies.
 
-## Installation
+## Features
 
-```
+- **HTTP Client**: Configurable Axios-based HTTP client with support for custom adapters
+- **Error Handling**: Comprehensive error classes for API and Contentstack-specific errors
+- **Request Management**: Request handling with interceptors and custom error callbacks
+- **Parameter Serialization**: Custom parameter serialization for API requests
+- **Retry Policies**: Built-in retry logic for handling rate limits and transient errors
+- **TypeScript Support**: Full TypeScript definitions included
+- **Multiple Build Formats**: Supports CommonJS, ESM, UMD, and TypeScript declarations
+
+## Important Note
+
+**This package is an internal dependency** used by Contentstack TypeScript SDKs. End users should **not** install this package directly. Instead, install the appropriate Contentstack SDK (e.g., [Contentstack TypeScript Delivery SDK](https://github.com/contentstack/contentstack-typescript/)), which will automatically include this package as a dependency.
+
+## For SDK Developers
+
+If you are developing or maintaining a Contentstack SDK and need to use this core package directly, you can install it as a dependency:
+
+```bash
 npm install @contentstack/core
 ```
 
-## Use case
+Then import the modules:
 
-This package contains some core modules and utilities used by the [Contentstack Typescript Delivery SDK](https://github.com/contentstack/contentstack-javascript/) SDK.
+```typescript
+import {
+  httpClient,
+  ContentstackError,
+  ApiError,
+  // ... other exports
+} from '@contentstack/core';
+```
 
 ## Development
 
-### Create the build:
+### Prerequisites
 
+- Node.js version 4.4.7 or later
+
+### Setup
+
+Clone the repository and install dependencies:
+
+```bash
+git clone https://github.com/contentstack/contentstack-js-core.git
+cd contentstack-js-core
+npm install
 ```
+
+### Build
+
+Build all output formats (CommonJS, ESM, UMD, and TypeScript declarations):
+
+```bash
 npm run build
 ```
 
-### Run Scripts:
-
-Run the unit tests:
+Build specific formats:
 
+```bash
+npm run build:cjs    # CommonJS
+npm run build:esm    # ES Modules
+npm run build:umd    # UMD
+npm run build:types  # TypeScript declarations
 ```
+
+### Testing
+
+Run unit tests:
+
+```bash
 npm run test
 ```
 
-Run the lint tests:
+Run linting:
 
-```
+```bash
 npm run lint
 ```
 
-Pack the SDK:
+### Packaging
 
-```
+Create a package tarball:
+
+```bash
 npm run package
-```
\ No newline at end of file
+```
+
+### Clean
+
+Clean build artifacts:
+
+```bash
+npm run clean
+```
+
+## License
+
+This project is licensed under the MIT License. See the [LICENSE.txt](LICENSE.txt) file for details.
+
+## Repository
+
+- **GitHub**: [contentstack/contentstack-js-core](https://github.com/contentstack/contentstack-js-core)
+
+## Related Projects
+
+- [Contentstack TypeScript Delivery SDK](https://github.com/contentstack/contentstack-javascript/)
+
+## Support
+
+For issues and feature requests, please visit the [GitHub Issues](https://github.com/contentstack/contentstack-js-core/issues) page.
+
+---
+
+Copyright (c) 2016-2025 Contentstack. All rights reserved.
diff --git a/package-lock.json b/package-lock.json
index f9b8547..8c42a23 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@contentstack/core",
-  "version": "1.3.7",
+  "version": "1.3.8",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@contentstack/core",
-      "version": "1.3.7",
+      "version": "1.3.8",
       "license": "MIT",
       "dependencies": {
         "axios": "^1.12.2",
diff --git a/package.json b/package.json
index 5675428..b712672 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@contentstack/core",
-  "version": "1.3.7",
+  "version": "1.3.8",
   "type": "commonjs",
   "main": "./dist/cjs/src/index.js",
   "types": "./dist/cjs/src/index.d.ts",
diff --git a/src/lib/contentstack-core.ts b/src/lib/contentstack-core.ts
index 15a1ac9..69f7b3c 100644
--- a/src/lib/contentstack-core.ts
+++ b/src/lib/contentstack-core.ts
@@ -1,4 +1,4 @@
-import { cloneDeep } from 'lodash';
+import _ from 'lodash';
 import { serialize } from './param-serializer';
 import axios, { AxiosRequestHeaders, getAdapter } from 'axios';
 import { AxiosInstance, HttpClientParams } from './types';
@@ -20,6 +20,7 @@ export function httpClient(options: HttpClientParams): AxiosInstance {
           const title = [data.name, data.message].filter((a) => a).join(' - ');
           console.error(ERROR_MESSAGES.CONSOLE.ERROR_WITH_TITLE(title));
         }
+
         return;
       }
       if (data !== undefined) {
@@ -38,7 +39,7 @@ export function httpClient(options: HttpClientParams): AxiosInstance {
 
   const config: HttpClientParams = {
     ...defaultConfig,
-    ...cloneDeep(options),
+    ..._.cloneDeep(options),
   };
 
   if (config.apiKey && config.headers) {
diff --git a/test/contentstack-core.spec.ts b/test/contentstack-core.spec.ts
index e69a7d3..c1bb031 100644
--- a/test/contentstack-core.spec.ts
+++ b/test/contentstack-core.spec.ts
@@ -2,9 +2,8 @@ import { AxiosInstance } from '../src';
 import { httpClient } from '../src/lib/contentstack-core';
 import MockAdapter from 'axios-mock-adapter';
 describe('contentstackCore', () => {
-  it('should return default config when no config is passed', (done) => {
-    const client = httpClient({});
-    done();
+  it('should return default config when no config is passed', () => {
+    httpClient({});
   });
 
   describe('logHandler', () => {
@@ -17,7 +16,9 @@ describe('contentstackCore', () => {
       const consoleErrorSpy = jest.spyOn(console, 'error').mockImplementation();
       httpClient({}).defaults.logHandler('error', error);
 
-      expect(consoleErrorSpy).toHaveBeenCalledWith('Error: Error - Something went wrong. Review the error details and try again.');
+      expect(consoleErrorSpy).toHaveBeenCalledWith(
+        'Error: Error - Something went wrong. Review the error details and try again.'
+      );
 
       consoleErrorSpy.mockRestore();
     });
@@ -152,7 +153,7 @@ describe('contentstackCore', () => {
     it('should call the onError function when an error occurs', async () => {
       // Suppress expected console.error from network error
       const consoleErrorSpy = jest.spyOn(console, 'error').mockImplementation();
-      
+
       const onError = jest.fn();
       const options = {
         defaultHostname: 'cdn.contentstack.io',
@@ -166,7 +167,7 @@ describe('contentstackCore', () => {
       } catch (error: unknown) {
         expect(onError).toBeCalledWith(error);
       }
-      
+
       consoleErrorSpy.mockRestore();
     });
 
@@ -188,4 +189,74 @@ describe('contentstackCore', () => {
       expect(client.httpClientParams.onError).not.toBeCalled();
     });
   });
+
+  describe('config deep cloning', () => {
+    it('should properly handle nested objects in params using cloneDeep', () => {
+      const options = {
+        defaultHostname: 'example.com',
+        params: {
+          environment: 'test',
+          nested: {
+            level1: {
+              level2: {
+                value: 'deep-nested',
+              },
+            },
+          },
+        },
+      };
+
+      const instance = httpClient(options);
+
+      // Verify nested structure is properly accessible
+      // This test ensures cloneDeep is working correctly (ESM import fix)
+      expect(instance.httpClientParams.params?.nested?.level1?.level2?.value).toBe('deep-nested');
+      expect(instance.httpClientParams.params?.environment).toBe('test');
+    });
+
+    it('should handle complex nested structures in params', () => {
+      const complexOptions = {
+        defaultHostname: 'example.com',
+        params: {
+          environment: 'production',
+          filters: {
+            category: {
+              name: 'tech',
+              tags: ['javascript', 'typescript'],
+            },
+          },
+        },
+      };
+
+      const instance = httpClient(complexOptions);
+
+      // Verify complex nested structure is properly handled
+      expect(instance.httpClientParams.params?.filters?.category?.name).toBe('tech');
+      expect(instance.httpClientParams.params?.filters?.category?.tags).toEqual(['javascript', 'typescript']);
+    });
+
+    it('should work correctly with lodash cloneDeep import (ESM compatibility)', () => {
+      // This test verifies that the lodash import works correctly in ESM
+      // by ensuring nested object cloning works as expected
+      const options = {
+        defaultHostname: 'example.com',
+        params: {
+          query: {
+            type: 'entry',
+            include: {
+              count: true,
+              schema: true,
+            },
+          },
+        },
+      };
+
+      const instance = httpClient(options);
+
+      // If cloneDeep wasn't working (due to import issues), this would fail
+      expect(instance.httpClientParams.params?.query?.type).toBe('entry');
+      expect(instance.httpClientParams.params?.query?.include?.count).toBe(true);
+      expect(instance.httpClientParams.params?.query?.include?.schema).toBe(true);
+    });
+  });
 });
diff --git a/tools/postbuild.js b/tools/postbuild.js
index 41b8cb6..45a1f37 100644
--- a/tools/postbuild.js
+++ b/tools/postbuild.js
@@ -5,6 +5,7 @@ const path = require('path');
  * Post-build script to create package.json in dist/esm/
  * This marks the ESM output directory as ES modules, resolving
  * the conflict with root package.json's "type": "commonjs"
+ * Also adds .js extensions to relative imports for ESM compatibility
  */
 const esmPackageJsonPath = path.join(__dirname, '../dist/esm/package.json');
 const esmPackageJson = {
@@ -19,3 +20,55 @@ if (!fs.existsSync(esmDir)) {
 
 // Write the package.json file
 fs.writeFileSync(esmPackageJsonPath, JSON.stringify(esmPackageJson, null, 2) + '\n', 'utf8');
+
+// Fix relative imports to include .js extensions for ESM compatibility
+const esmSrcDir = path.join(__dirname, '../dist/esm/src');
+
+function fixImportsInFile(filePath) {
+  const content = fs.readFileSync(filePath, 'utf8');
+
+  // Replace relative imports/exports without .js extension
+  // Matches: './something' or '../something' but not './something.js' or './something.json'
+  const fixedContent = content
+    .replace(/(from\s+['"])(\.\.?\/[^'"]+)(['"])/g, (match, prefix, importPath, suffix) => {
+      // Skip if already has extension or is a JSON import
+      if (importPath.endsWith('.js') || importPath.endsWith('.json') || importPath.endsWith('.mjs')) {
+        return match;
+      }
+
+      // Add .js extension
+      return `${prefix}${importPath}.js${suffix}`;
+    })
+    .replace(/(export\s+\*\s+from\s+['"])(\.\.?\/[^'"]+)(['"])/g, (match, prefix, importPath, suffix) => {
+      // Skip if already has extension or is a JSON import
+      if (importPath.endsWith('.js') || importPath.endsWith('.json') || importPath.endsWith('.mjs')) {
+        return match;
+      }
+
+      // Add .js extension
+      return `${prefix}${importPath}.js${suffix}`;
+    });
+
+  if (content !== fixedContent) {
+    fs.writeFileSync(filePath, fixedContent, 'utf8');
+  }
+}
+
+function processDirectory(dir) {
+  const entries = fs.readdirSync(dir, { withFileTypes: true });
+
+  for (const entry of entries) {
+    const fullPath = path.join(dir, entry.name);
+
+    if (entry.isDirectory()) {
+      processDirectory(fullPath);
+    } else if (entry.isFile() && entry.name.endsWith('.js')) {
+      fixImportsInFile(fullPath);
+    }
+  }
+}
+
+// Process all .js files in the ESM build
+if (fs.existsSync(esmSrcDir)) {
+  processDirectory(esmSrcDir);
+}