diff --git a/ts/components/ProfileEditor.tsx b/ts/components/ProfileEditor.tsx
index dea2d82cd..8af8ebdf3 100644
--- a/ts/components/ProfileEditor.tsx
+++ b/ts/components/ProfileEditor.tsx
@@ -35,6 +35,7 @@ import {
 } from './conversation/conversation-details/ConversationDetailsIcon';
 import { Spinner } from './Spinner';
 import { UsernameSaveState } from '../state/ducks/conversationsEnums';
+import { MAX_USERNAME, MIN_USERNAME } from '../types/Username';
 
 export enum EditState {
   None = 'None',
@@ -123,26 +124,24 @@ function getUsernameInvalidKey(
     return undefined;
   }
 
-  const min = 3;
-  if (username.length < min) {
+  if (username.length < MIN_USERNAME) {
     return {
       key: 'ProfileEditor--username--check-character-min',
-      replacements: { min },
+      replacements: { min: MIN_USERNAME },
     };
   }
 
   if (!/^[0-9a-z_]+$/.test(username)) {
     return { key: 'ProfileEditor--username--check-characters' };
   }
-  if (/^[0-9]/.test(username)) {
+  if (!/^[a-z_]/.test(username)) {
     return { key: 'ProfileEditor--username--check-starting-character' };
   }
 
-  const max = 25;
-  if (username.length > max) {
+  if (username.length > MAX_USERNAME) {
     return {
       key: 'ProfileEditor--username--check-character-max',
-      replacements: { max },
+      replacements: { max: MAX_USERNAME },
     };
   }
 
diff --git a/ts/test-node/types/Username_test.ts b/ts/test-node/types/Username_test.ts
new file mode 100644
index 000000000..016161b93
--- /dev/null
+++ b/ts/test-node/types/Username_test.ts
@@ -0,0 +1,79 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+
+import * as Username from '../../types/Username';
+
+describe('Username', () => {
+  describe('getUsernameFromSearch', () => {
+    const { getUsernameFromSearch } = Username;
+
+    it('matches invalid username searches', () => {
+      assert.strictEqual(getUsernameFromSearch('username!'), 'username!');
+      assert.strictEqual(getUsernameFromSearch('1username'), '1username');
+      assert.strictEqual(getUsernameFromSearch('use'), 'use');
+      assert.strictEqual(
+        getUsernameFromSearch('username9012345678901234567'),
+        'username9012345678901234567'
+      );
+    });
+
+    it('matches valid username searches', () => {
+      assert.strictEqual(getUsernameFromSearch('username_34'), 'username_34');
+      assert.strictEqual(getUsernameFromSearch('u5ername'), 'u5ername');
+      assert.strictEqual(getUsernameFromSearch('user'), 'user');
+      assert.strictEqual(
+        getUsernameFromSearch('username901234567890123456'),
+        'username901234567890123456'
+      );
+    });
+
+    it('matches valid and invalid usernames with @ prefix', () => {
+      assert.strictEqual(getUsernameFromSearch('@username!'), 'username!');
+      assert.strictEqual(getUsernameFromSearch('@1username'), '1username');
+      assert.strictEqual(getUsernameFromSearch('@username_34'), 'username_34');
+      assert.strictEqual(getUsernameFromSearch('@u5ername'), 'u5ername');
+    });
+
+    it('matches valid and invalid usernames with @ suffix', () => {
+      assert.strictEqual(getUsernameFromSearch('username!@'), 'username!');
+      assert.strictEqual(getUsernameFromSearch('1username@'), '1username');
+      assert.strictEqual(getUsernameFromSearch('username_34@'), 'username_34');
+      assert.strictEqual(getUsernameFromSearch('u5ername@'), 'u5ername');
+    });
+
+    it('does not match something that looks like a phone number', () => {
+      assert.isUndefined(getUsernameFromSearch('+'));
+      assert.isUndefined(getUsernameFromSearch('2223'));
+      assert.isUndefined(getUsernameFromSearch('+3'));
+      assert.isUndefined(getUsernameFromSearch('+234234234233'));
+    });
+  });
+
+  describe('isValidUsername', () => {
+    const { isValidUsername } = Username;
+
+    it('does not match invalid username searches', () => {
+      assert.isFalse(isValidUsername('username!'));
+      assert.isFalse(isValidUsername('1username'));
+      assert.isFalse(isValidUsername('use'));
+      assert.isFalse(isValidUsername('username9012345678901234567'));
+    });
+
+    it('matches valid usernames', () => {
+      assert.isTrue(isValidUsername('username_34'));
+      assert.isTrue(isValidUsername('u5ername'));
+      assert.isTrue(isValidUsername('_username'));
+      assert.isTrue(isValidUsername('user'));
+      assert.isTrue(isValidUsername('username901234567890123456'));
+    });
+
+    it('does not match valid and invalid usernames with @ prefix or suffix', () => {
+      assert.isFalse(isValidUsername('@username_34'));
+      assert.isFalse(isValidUsername('@1username'));
+      assert.isFalse(isValidUsername('username_34@'));
+      assert.isFalse(isValidUsername('1username@'));
+    });
+  });
+});
diff --git a/ts/types/Username.ts b/ts/types/Username.ts
new file mode 100644
index 000000000..d4699fe5d
--- /dev/null
+++ b/ts/types/Username.ts
@@ -0,0 +1,23 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+export const MAX_USERNAME = 26;
+export const MIN_USERNAME = 4;
+
+export function isValidUsername(searchTerm: string): boolean {
+  return /^[a-z_][0-9a-z_]{3,25}$/.test(searchTerm);
+}
+
+export function getUsernameFromSearch(searchTerm: string): string | undefined {
+  if (/^[+0-9]+$/.test(searchTerm)) {
+    return undefined;
+  }
+
+  const match = /^@?(.*?)@?$/.exec(searchTerm);
+
+  if (match && match[1]) {
+    return match[1];
+  }
+
+  return undefined;
+}