diff --git a/README.md b/README.md
new file mode 100644
index 0000000..7381697
--- /dev/null
+++ b/README.md
@@ -0,0 +1,28 @@
+# @internxt/lib
+
+Common logic shared between different projects of Internxt.
+
+A zero-dependency TypeScript library providing utilities for AES-256-GCM encryption, authentication helpers (email/password validation, JWT token handling), file/item naming, and string manipulation.
+
+## Installation
+
+```sh
+npm install @internxt/lib
+```
+
+## Development
+
+```sh
+# Install dependencies
+npm install
+
+# Run tests
+npm run test
+
+# Build
+npm run build
+```
+
+## License
+
+[MIT](LICENSE)
diff --git a/package.json b/package.json
index e62fdde..c1e77b1 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@internxt/lib",
-  "version": "1.5.0",
+  "version": "1.5.1",
   "description": "Common logic shared between different projects of Internxt ",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
diff --git a/src/auth/validateJwtAndCheckExpiration.ts b/src/auth/validateJwtAndCheckExpiration.ts
index d5be35f..77f1ccf 100644
--- a/src/auth/validateJwtAndCheckExpiration.ts
+++ b/src/auth/validateJwtAndCheckExpiration.ts
@@ -3,8 +3,12 @@ export interface DecodedJwtClaims {
   iat: number | null;
 }
 
+function decodeBase64UrlSegment(seg: string): string {
+  return Buffer.from(seg.replace(/-/g, '+').replace(/_/g, '/'), 'base64').toString();
+}
+
 /**
- * Validates JWT token structure and parses the expiration and issued-at claims.
+ * Validates JWT token structure, header (presence of alg), and parses the expiration and issued-at claims.
  * Does not verify signature or issuer.
  * @returns The exp and iat claims (iat is null if absent), or null if invalid structure
  */
@@ -14,10 +18,18 @@ export default function validateJwtAndCheckExpiration(token: string): DecodedJwt
   }
 
   try {
-    const payload = JSON.parse(atob(token.split('.')[1]));
-    if (typeof payload.exp !== 'number') {
+    const [headerSeg, payloadSeg] = token.split('.');
+
+    const header = JSON.parse(decodeBase64UrlSegment(headerSeg));
+    if (typeof header.alg !== 'string') {
       return null;
     }
+
+    const payload = JSON.parse(decodeBase64UrlSegment(payloadSeg));
+    if (typeof payload.exp !== 'number' || payload.exp < 0) {
+      return null;
+    }
+
     return {
       exp: payload.exp,
       iat: typeof payload.iat === 'number' ? payload.iat : null,
diff --git a/test/auth/validateJwtAndCheckExpiration.test.ts b/test/auth/validateJwtAndCheckExpiration.test.ts
index 2e7a6b8..8c5093d 100644
--- a/test/auth/validateJwtAndCheckExpiration.test.ts
+++ b/test/auth/validateJwtAndCheckExpiration.test.ts
@@ -12,37 +12,71 @@ describe('validateJwtAndCheckExpiration tests', () => {
   });
 
   test('when the token payload is not valid base64 encoding, then null is returned', () => {
-    const invalidToken = 'header.!!!invalid_base64!!!.signature';
+    const invalidToken = 'eyJhbGciOiJIUzI1NiJ9.!!!invalid_base64!!!.signature';
     expect(validateJwtAndCheckExpiration(invalidToken)).to.be.equal(null);
   });
 
+  test('when the token header is not valid JSON, then null is returned', () => {
+    const token = 'invalid-json.eyJzdWIiOiJ1c2VyMTIzIn0=.signature';
+    expect(validateJwtAndCheckExpiration(token)).to.be.equal(null);
+  });
+
+  test('when the token header is missing the alg field, then null is returned', () => {
+    const header = Buffer.from(JSON.stringify({ typ: 'JWT' })).toString('base64');
+    const payload = Buffer.from(JSON.stringify({ exp: Math.floor(Date.now() / 1000) + 3600 })).toString('base64');
+    const token = `${header}.${payload}.signature`;
+    expect(validateJwtAndCheckExpiration(token)).to.be.equal(null);
+  });
+
+  test('when the token has a negative expiration value, then null is returned', () => {
+    const payload = Buffer.from(JSON.stringify({ exp: -1 })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
+    expect(validateJwtAndCheckExpiration(token)).to.be.equal(null);
+  });
+
   test('when the token does not contain an expiration claim, then null is returned', () => {
-    const payload = btoa(JSON.stringify({ sub: 'user123' }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ sub: 'user123' })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
     expect(validateJwtAndCheckExpiration(token)).to.be.equal(null);
   });
 
   test('when the token expiration value is not a number, then null is returned', () => {
-    const payload = btoa(JSON.stringify({ exp: 'not-a-number' }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: 'not-a-number' })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
     expect(validateJwtAndCheckExpiration(token)).to.be.equal(null);
   });
 
   test('when the token has a valid structure with expiration, then the exp and iat claims are returned', () => {
     const expiration = Math.floor(Date.now() / 1000) + 3600; // 1 hour from now
-    const payload = btoa(JSON.stringify({ exp: expiration, sub: 'user123' }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: expiration, sub: 'user123' })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
     expect(validateJwtAndCheckExpiration(token)).to.deep.equal({
       exp: expiration,
       iat: null,
     });
   });
 
+  test('when the token payload is base64url-encoded with characters outside the standard alphabet, then the claims are returned', () => {
+    const issuedAt = 1577836800;
+    const expiration = 4102444800;
+    // Payload encodes to a segment containing both - and _ (base64url alphabet)
+    const payload = Buffer.from(JSON.stringify({ exp: expiration, iat: issuedAt, sub: 'WO¥þ=(E' })).toString(
+      'base64url',
+    );
+    expect(payload).to.match(/-/);
+    expect(payload).to.match(/_/);
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
+    expect(validateJwtAndCheckExpiration(token)).to.deep.equal({
+      exp: expiration,
+      iat: issuedAt,
+    });
+  });
+
   test('when the token has a valid structure with expiration and issued-at, then both claims are returned', () => {
     const issuedAt = Math.floor(Date.now() / 1000);
     const expiration = issuedAt + 3600; // 1 hour from now
-    const payload = btoa(JSON.stringify({ exp: expiration, iat: issuedAt, sub: 'user123' }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: expiration, iat: issuedAt, sub: 'user123' })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
     expect(validateJwtAndCheckExpiration(token)).to.deep.equal({
       exp: expiration,
       iat: issuedAt,
diff --git a/test/auth/validateTokenAndCheckExpiration.test.ts b/test/auth/validateTokenAndCheckExpiration.test.ts
index b4a6c98..53ab329 100644
--- a/test/auth/validateTokenAndCheckExpiration.test.ts
+++ b/test/auth/validateTokenAndCheckExpiration.test.ts
@@ -10,16 +10,16 @@ describe('validateTokenAndCheckExpiration tests', () => {
 
   test('when the token is structurally valid but has expired, then EXPIRED is returned', () => {
     const expiration = Math.floor(Date.now() / 1000) - 3600; // 1 hour ago
-    const payload = btoa(JSON.stringify({ exp: expiration }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: expiration })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
 
     expect(validateTokenAndCheckExpiration(token)).to.be.equal(TokenStatus.EXPIRED);
   });
 
   test('when the token is valid and expires within six hours, then REFRESH_REQUIRED is returned', () => {
     const expiration = Math.floor(Date.now() / 1000) + 6 * 60 * 60; // 6 hours from now
-    const payload = btoa(JSON.stringify({ exp: expiration }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: expiration })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
 
     expect(validateTokenAndCheckExpiration(token)).to.be.equal(TokenStatus.REFRESH_REQUIRED);
   });
@@ -27,16 +27,16 @@ describe('validateTokenAndCheckExpiration tests', () => {
   test('when the token is valid, has an issued-at claim, and is past 50% of its lifetime, then REFRESH_REQUIRED is returned', () => {
     const issuedAt = Math.floor(Date.now() / 1000) - 16 * 60 * 60; // issued 16h ago
     const expiration = issuedAt + 32 * 60 * 60; // total lifetime 32h, 16h (50%) remaining
-    const payload = btoa(JSON.stringify({ exp: expiration, iat: issuedAt }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: expiration, iat: issuedAt })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
 
     expect(validateTokenAndCheckExpiration(token)).to.be.equal(TokenStatus.REFRESH_REQUIRED);
   });
 
   test('when the token is valid and expires in thirty days, then VALID is returned', () => {
     const expiration = Math.floor(Date.now() / 1000) + 30 * 24 * 60 * 60; // 30 days from now
-    const payload = btoa(JSON.stringify({ exp: expiration }));
-    const token = `header.${payload}.signature`;
+    const payload = Buffer.from(JSON.stringify({ exp: expiration })).toString('base64');
+    const token = `eyJhbGciOiJIUzI1NiJ9.${payload}.signature`;
 
     expect(validateTokenAndCheckExpiration(token)).to.be.equal(TokenStatus.VALID);
   });
diff --git a/test/tsconfig.json b/test/tsconfig.json
new file mode 100644
index 0000000..ffac201
--- /dev/null
+++ b/test/tsconfig.json
@@ -0,0 +1,6 @@
+{
+  "compilerOptions": {
+    "types": ["node"]
+  },
+  "include": ["./**/*.ts"]
+}