diff --git a/server/package-lock.json b/server/package-lock.json
index 5f40d7a..63103cb 100644
--- a/server/package-lock.json
+++ b/server/package-lock.json
@@ -21,7 +21,8 @@
         "pm2": "^5.2.0",
         "sqlite": "^4.0.23",
         "sqlite3": "^5.1.1",
-        "ts-node": "^10.9.1"
+        "ts-node": "^10.9.1",
+        "validator": "^13.9.0"
       },
       "devDependencies": {
         "@types/cors": "^2.8.12",
@@ -29,6 +30,7 @@
         "@types/jest": "^28.1.8",
         "@types/jsonwebtoken": "^8.5.8",
         "@types/supertest": "^2.0.12",
+        "@types/validator": "^13.7.17",
         "jest": "^29.0.3",
         "supertest": "^6.2.4",
         "ts-jest": "^29.0.0",
@@ -2125,6 +2127,12 @@
         "@types/superagent": "*"
       }
     },
+    "node_modules/@types/validator": {
+      "version": "13.7.17",
+      "resolved": "https://registry.npmjs.org/@types/validator/-/validator-13.7.17.tgz",
+      "integrity": "sha512-aqayTNmeWrZcvnG2MG9eGYI6b7S5fl+yKgPs6bAjOTwPS316R5SxBGKvtSExfyoJU7pIeHJfsHI0Ji41RVMkvQ==",
+      "dev": true
+    },
     "node_modules/@types/yargs": {
       "version": "17.0.10",
       "resolved": "https://registry.npmjs.org/@types/yargs/-/yargs-17.0.10.tgz",
@@ -8771,6 +8779,14 @@
         "node": ">=10.12.0"
       }
     },
+    "node_modules/validator": {
+      "version": "13.9.0",
+      "resolved": "https://registry.npmjs.org/validator/-/validator-13.9.0.tgz",
+      "integrity": "sha512-B+dGG8U3fdtM0/aNK4/X8CXq/EcxU2WPrPEkJGslb47qyHsxmbggTWK0yEA4qnYVNF+nxNlN88o14hIcPmSIEA==",
+      "engines": {
+        "node": ">= 0.10"
+      }
+    },
     "node_modules/vary": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/vary/-/vary-1.1.2.tgz",
@@ -10697,6 +10713,12 @@
         "@types/superagent": "*"
       }
     },
+    "@types/validator": {
+      "version": "13.7.17",
+      "resolved": "https://registry.npmjs.org/@types/validator/-/validator-13.7.17.tgz",
+      "integrity": "sha512-aqayTNmeWrZcvnG2MG9eGYI6b7S5fl+yKgPs6bAjOTwPS316R5SxBGKvtSExfyoJU7pIeHJfsHI0Ji41RVMkvQ==",
+      "dev": true
+    },
     "@types/yargs": {
       "version": "17.0.10",
       "resolved": "https://registry.npmjs.org/@types/yargs/-/yargs-17.0.10.tgz",
@@ -15713,6 +15735,11 @@
         "convert-source-map": "^1.6.0"
       }
     },
+    "validator": {
+      "version": "13.9.0",
+      "resolved": "https://registry.npmjs.org/validator/-/validator-13.9.0.tgz",
+      "integrity": "sha512-B+dGG8U3fdtM0/aNK4/X8CXq/EcxU2WPrPEkJGslb47qyHsxmbggTWK0yEA4qnYVNF+nxNlN88o14hIcPmSIEA=="
+    },
     "vary": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/vary/-/vary-1.1.2.tgz",
diff --git a/server/package.json b/server/package.json
index 2d051e1..f2a2e58 100644
--- a/server/package.json
+++ b/server/package.json
@@ -25,7 +25,8 @@
     "pm2": "^5.2.0",
     "sqlite": "^4.0.23",
     "sqlite3": "^5.1.1",
-    "ts-node": "^10.9.1"
+    "ts-node": "^10.9.1",
+    "validator": "^13.9.0"
   },
   "devDependencies": {
     "@types/cors": "^2.8.12",
@@ -33,6 +34,7 @@
     "@types/jest": "^28.1.8",
     "@types/jsonwebtoken": "^8.5.8",
     "@types/supertest": "^2.0.12",
+    "@types/validator": "^13.7.17",
     "jest": "^29.0.3",
     "supertest": "^6.2.4",
     "ts-jest": "^29.0.0",
diff --git a/server/src/handlers/userHandler.ts b/server/src/handlers/userHandler.ts
index 6f29209..e8700b3 100644
--- a/server/src/handlers/userHandler.ts
+++ b/server/src/handlers/userHandler.ts
@@ -17,6 +17,7 @@ import crypto from 'crypto';
 import { signJwt } from '../auth';
 import { Datastore } from '../datastore';
 import { ExpressHandler, ExpressHandlerWithParams } from '../types';
+import validator from 'validator'
 
 export class UserHandler {
   private db: Datastore;
@@ -57,6 +58,12 @@ export class UserHandler {
       return res.status(400).send({ error: ERRORS.USER_REQUIRED_FIELDS });
     }
 
+    if (!validator.isEmail(email)) return res.status(400).send({ error: ERRORS.INVALID_EMAIL});
+    if (!validator.isAlphanumeric(userName)) return res.status(400).send({ error: ERRORS.INVALID_USERNAME});
+    if (!validator.isStrongPassword(password)) return res.status(400).send({ error: ERRORS.WEAK_PASSWORD});
+    if (firstName && !validator.isAlphanumeric(firstName)) return res.status(400).send({ error: ERRORS.INVALID_FIRSTNAME});
+    if (lastName && !validator.isAlphanumeric(lastName)) return res.status(400).send({ error: ERRORS.INVALID_LASTNAME});
+
     if (await this.db.getUserByEmail(email)) {
       return res.status(403).send({ error: ERRORS.DUPLICATE_EMAIL });
     }
@@ -121,6 +128,8 @@ export class UserHandler {
       const currentUserId = res.locals.userId;
       const { userName } = req.body;
 
+      if (userName && !validator.isAlphanumeric(userName)) return res.status(400).send({ error: ERRORS.INVALID_USERNAME});
+
       if (userName && (await this.isDuplicateUserName(currentUserId, userName))) {
         return res.status(403).send({ error: ERRORS.DUPLICATE_USERNAME });
       }
diff --git a/shared/src/errors.ts b/shared/src/errors.ts
index cd2c451..ea56858 100644
--- a/shared/src/errors.ts
+++ b/shared/src/errors.ts
@@ -6,6 +6,11 @@ export enum ERRORS {
   USER_REQUIRED_FIELDS = 'Email, username, and password are required',
   DUPLICATE_EMAIL = 'An account with this email already exists',
   DUPLICATE_USERNAME = 'An account with this username already exists',
+  INVALID_EMAIL = 'Invalid email',
+  WEAK_PASSWORD = 'Weak password',
+  INVALID_USERNAME = 'Username must have only letters and numbers',
+  INVALID_FIRSTNAME = 'First name must have only letters and numbers',
+  INVALID_LASTNAME = 'Last name must have only letters and numbers',
 
   POST_ID_MISSING = 'Post ID is missing',
   POST_NOT_FOUND = 'Post not found',