diff --git a/.vscode/settings.json b/.vscode/settings.json
index 87ca8efb..e426a5e1 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,18 +1,21 @@
 {
-    "spellchecker.ignoreWordsList": [
-        "mTLS",
-        "Wireguard"
-    ],
-    "sqltools.connections": [
-        {
-            "previewLimit": 50,
-            "server": "localhost",
-            "port": 5432,
-            "driver": "PostgreSQL",
-            "name": "drop",
-            "database": "drop",
-            "username": "drop",
-            "password": "drop"
-        }
-    ]
+  "spellchecker.ignoreWordsList": ["mTLS", "Wireguard"],
+  "sqltools.connections": [
+    {
+      "previewLimit": 50,
+      "server": "localhost",
+      "port": 5432,
+      "driver": "PostgreSQL",
+      "name": "drop",
+      "database": "drop",
+      "username": "drop",
+      "password": "drop"
+    }
+  ],
+  // allow autocomplete for ArkType expressions like "string | num"
+  "editor.quickSuggestions": {
+    "strings": "on"
+  },
+  // prioritize ArkType's "type" for autoimports
+  "typescript.preferences.autoImportSpecifierExcludeRegexes": ["^(node:)?os$"]
 }
diff --git a/package.json b/package.json
index c114de5a..b05f39ba 100644
--- a/package.json
+++ b/package.json
@@ -19,6 +19,7 @@
     "@prisma/client": "^6.1.0",
     "@tailwindcss/vite": "^4.0.6",
     "argon2": "^0.41.1",
+    "arktype": "^2.1.10",
     "axios": "^1.7.7",
     "bcryptjs": "^2.4.3",
     "cookie-es": "^1.2.2",
diff --git a/pages/register.vue b/pages/register.vue
index 4a7b018c..5574ab44 100644
--- a/pages/register.vue
+++ b/pages/register.vue
@@ -188,6 +188,7 @@
 
 <script setup lang="ts">
 import { XCircleIcon } from "@heroicons/vue/24/solid";
+import { type } from "arktype";
 
 const route = useRoute();
 const router = useRouter();
@@ -208,14 +209,20 @@ const username = ref(invitation.data.value?.username);
 const password = ref("");
 const confirmPassword = ref(undefined);
 
-const mailRegex = /^\S+@\S+\.\S+$/;
-const validEmail = computed(() => mailRegex.test(email.value ?? ""));
-const validUsername = computed(
-  () =>
-    (username.value?.length ?? 0) >= 5 &&
-    username.value?.toLowerCase() == username.value
+const emailValidator = type("string.email");
+const validEmail = computed(
+  () => !(emailValidator(email.value) instanceof type.errors)
+);
+
+const usernameValidator = type("string.lower.preformatted >= 5");
+const validUsername = computed(
+  () => !(usernameValidator(username.value) instanceof type.errors)
+);
+
+const passwordValidator = type("string >= 14");
+const validPassword = computed(
+  () => !(passwordValidator(password.value) instanceof type.errors)
 );
-const validPassword = computed(() => (password.value?.length ?? 0) >= 14);
 const validConfirmPassword = computed(
   () => password.value == confirmPassword.value
 );
diff --git a/server/api/v1/auth/signup/simple.post.ts b/server/api/v1/auth/signup/simple.post.ts
index 0e1c6f1f..4d31cf77 100644
--- a/server/api/v1/auth/signup/simple.post.ts
+++ b/server/api/v1/auth/signup/simple.post.ts
@@ -4,9 +4,15 @@ import { createHashArgon2 } from "~/server/internal/security/simple";
 import { v4 as uuidv4 } from "uuid";
 import * as jdenticon from "jdenticon";
 import objectHandler from "~/server/internal/objects";
+import { type } from "arktype";
+import { writeNonLiteralDefaultMessage } from "arktype/internal/parser/shift/operator/default.ts";
 
-// Only really a simple test, in case people mistype their emails
-const mailRegex = /^\S+@\S+\.\S+$/;
+const userValidator = type({
+  username: "string >= 5",
+  email: "string.email",
+  password: "string >= 14",
+  "displayName?": "string | undefined",
+});
 
 export default defineEventHandler(async (h3) => {
   const body = await readBody(h3);
@@ -27,59 +33,24 @@ export default defineEventHandler(async (h3) => {
       statusMessage: "Invalid or expired invitation.",
     });
 
-  const useInvitationOrBodyRequirement = (
-    field: keyof Invitation,
-    check: (v: string) => boolean
-  ) => {
-    if (invitation[field]) {
-      return invitation[field].toString();
-    }
+  const user = userValidator(body);
+  if (user instanceof type.errors) {
+    // hover out.summary to see validation errors
+    console.error(user.summary);
 
-    const v: string = body[field]?.toString();
-    const valid = check(v);
-    return valid ? v : undefined;
-  };
-
-  const username = useInvitationOrBodyRequirement(
-    "username",
-    (e) => e.length >= 5
-  );
-  const email = useInvitationOrBodyRequirement("email", (e) =>
-    mailRegex.test(e)
-  );
-  const password = body.password;
-  const displayName = body.displayName || username;
-
-  if (username === undefined)
     throw createError({
       statusCode: 400,
-      statusMessage: "Username is invalid. Must be more than 5 characters.",
-    });
-  if (username.toLowerCase() != username)
-    throw createError({
-      statusCode: 400,
-      statusMessage: "Username must be all lowercase",
+      statusMessage: user.summary,
     });
+  }
 
-  if (email === undefined)
-    throw createError({
-      statusCode: 400,
-      statusMessage: "Invalid email. Must follow the format you@example.com",
-    });
+  // reuse items from invite
+  if (invitation.username !== null) user.username = invitation.username;
+  if (invitation.email !== null) user.email = invitation.email;
 
-  if (!password)
-    throw createError({
-      statusCode: 400,
-      statusMessage: "Password empty or missing.",
-    });
-
-  if (password.length < 14)
-    throw createError({
-      statusCode: 400,
-      statusMessage: "Password must be 14 or more characters.",
-    });
-
-  const existing = await prisma.user.count({ where: { username: username } });
+  const existing = await prisma.user.count({
+    where: { username: user.username },
+  });
   if (existing > 0)
     throw createError({
       statusCode: 400,
@@ -91,12 +62,12 @@ export default defineEventHandler(async (h3) => {
   const profilePictureId = uuidv4();
   await objectHandler.createFromSource(
     profilePictureId,
-    async () => jdenticon.toPng(username, 256),
+    async () => jdenticon.toPng(user.username, 256),
     {},
     [`internal:read`, `${userId}:write`]
   );
 
-  const hash = await createHashArgon2(password);
+  const hash = await createHashArgon2(user.password);
   const [linkMec] = await prisma.$transaction([
     prisma.linkedAuthMec.create({
       data: {
@@ -106,9 +77,9 @@ export default defineEventHandler(async (h3) => {
         user: {
           create: {
             id: userId,
-            username,
-            displayName,
-            email,
+            username: user.username,
+            displayName: user.displayName ?? user.username,
+            email: user.email,
             profilePicture: profilePictureId,
             admin: invitation.isAdmin,
           },
diff --git a/server/tsconfig.json b/server/tsconfig.json
index b9ed69c1..ca5c731e 100644
--- a/server/tsconfig.json
+++ b/server/tsconfig.json
@@ -1,3 +1,6 @@
 {
-  "extends": "../.nuxt/tsconfig.server.json"
+  "extends": "../.nuxt/tsconfig.server.json",
+  "compilerOptions": {
+    "exactOptionalPropertyTypes": true
+  }
 }
diff --git a/tsconfig.json b/tsconfig.json
index a746f2a7..5510f189 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,4 +1,7 @@
 {
   // https://nuxt.com/docs/guide/concepts/typescript
-  "extends": "./.nuxt/tsconfig.json"
+  "extends": "./.nuxt/tsconfig.json",
+  "compilerOptions": {
+    "exactOptionalPropertyTypes": true
+  }
 }
diff --git a/yarn.lock b/yarn.lock
index baaaabe9..ae9b48c9 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -20,6 +20,18 @@
   resolved "https://registry.yarnpkg.com/@antfu/utils/-/utils-0.7.10.tgz#ae829f170158e297a9b6a28f161a8e487d00814d"
   integrity sha512-+562v9k4aI80m1+VuMHehNJWLOFjBnXn3tdOitzD0il5b7smkSBal4+a3oKiQTbrwMmN/TBUMDvbdoWDehgOww==
 
+"@ark/schema@0.45.0":
+  version "0.45.0"
+  resolved "https://registry.yarnpkg.com/@ark/schema/-/schema-0.45.0.tgz#5d5da5dfe94ca45d36d54513fe0c53566483a1e7"
+  integrity sha512-3XlMWkZbEjh0YsF92vnnRNCWNRNhRKDTf6XhugyCXH0YRFuM+w1vFLDbB2JLfZloEd7i5cbqsLaDLzyBZbPrSg==
+  dependencies:
+    "@ark/util" "0.45.0"
+
+"@ark/util@0.45.0":
+  version "0.45.0"
+  resolved "https://registry.yarnpkg.com/@ark/util/-/util-0.45.0.tgz#2c55394a6af7865aeeb22924f301e28084aea4c0"
+  integrity sha512-Z1gHEGbpPzLtPmYb932t2B++6YonlUi1Fa14IQ4vhsGMWhd81Mi1miUmdZXW4fNI/wg1saT7H2/5cAuONgTXhg==
+
 "@babel/code-frame@^7.12.13", "@babel/code-frame@^7.22.13", "@babel/code-frame@^7.24.7", "@babel/code-frame@^7.25.9", "@babel/code-frame@^7.26.0", "@babel/code-frame@^7.26.2":
   version "7.26.2"
   resolved "https://registry.yarnpkg.com/@babel/code-frame/-/code-frame-7.26.2.tgz#4b5fab97d33338eff916235055f0ebc21e573a85"
@@ -2106,6 +2118,14 @@ argparse@^2.0.1:
   resolved "https://registry.yarnpkg.com/argparse/-/argparse-2.0.1.tgz#246f50f3ca78a3240f6c997e8a9bd1eac49e4b38"
   integrity sha512-8+9WqebbFzpX9OR+Wa6O29asIogeRMzcGtAINdpMHHyAg10f05aSFVBbcEqGf/PXw1EjAZ+q2/bEBg3DvurK3Q==
 
+arktype@^2.1.10:
+  version "2.1.10"
+  resolved "https://registry.yarnpkg.com/arktype/-/arktype-2.1.10.tgz#7a2fb85d1e8fbb22077134993a12e9b12d34ef6e"
+  integrity sha512-KqbrzI9qIGrQUClifyS1HpUp/oTSRtGDvnMKzwg2TAvxRpynY1mn/ubXaxAAdGPOM8V3pBqwb01Z6TcXqhBxzQ==
+  dependencies:
+    "@ark/schema" "0.45.0"
+    "@ark/util" "0.45.0"
+
 ast-kit@^1.0.1, ast-kit@^1.3.0:
   version "1.3.0"
   resolved "https://registry.yarnpkg.com/ast-kit/-/ast-kit-1.3.0.tgz#37c8b7418b6c59b1e593d7790dc6c2b1c0814761"