diff --git a/src/features/layout/LeftNavBar.tsx b/src/features/layout/LeftNavBar.tsx
index 32817209..e6274be1 100644
--- a/src/features/layout/LeftNavBar.tsx
+++ b/src/features/layout/LeftNavBar.tsx
@@ -72,7 +72,7 @@ const LeftNavBar: FC = () => {
           icon={faDatabase}
           badge={'alpha'}
           badgeColor={'warning'}
-          requiredRole="CDM_JUPYTERHUB_ADMIN"
+          requiredRole="BERDL_USER"
         />
       </ul>
       <ul className={classes.nav_list}>
diff --git a/src/features/signup/AccountInformation.test.tsx b/src/features/signup/AccountInformation.test.tsx
index d491669b..82911794 100644
--- a/src/features/signup/AccountInformation.test.tsx
+++ b/src/features/signup/AccountInformation.test.tsx
@@ -135,4 +135,72 @@ describe('AccountInformation', () => {
 
     expect(mockNavigate).toHaveBeenCalledWith('/signup/3');
   });
+
+  test.each([
+    ['uppercase letters', 'BadUser'],
+    ['a leading digit', '1baduser'],
+    ['a hyphen', 'bad-user'],
+    ['a period', 'bad.user'],
+    ['repeating underscores', 'bad__user'],
+    ['a trailing underscore', 'baduser_'],
+  ])(
+    'blocks submission and shows format error for username with %s',
+    async (_label, badName) => {
+      const store = createTestStore();
+      store.dispatch(
+        setLoginData({
+          creationallowed: true,
+          expires: 0,
+          login: [],
+          provider: 'Google',
+          create: [
+            {
+              provemail: 'test@test.com',
+              provfullname: 'Test User',
+              availablename: 'testuser',
+              id: '123',
+              provusername: 'testuser',
+            },
+          ],
+        })
+      );
+      renderWithProviders(<AccountInformation />, { store });
+
+      await act(() => {
+        fireEvent.change(screen.getByRole('textbox', { name: /Full Name/i }), {
+          target: { value: 'Test User' },
+        });
+      });
+      await act(() => {
+        fireEvent.change(screen.getByRole('textbox', { name: /Email/i }), {
+          target: { value: 'test@test.com' },
+        });
+      });
+      await act(() => {
+        fireEvent.change(
+          screen.getByRole('textbox', { name: /KBase Username/i }),
+          { target: { value: badName } }
+        );
+      });
+      await act(() => {
+        fireEvent.change(
+          screen.getByRole('textbox', { name: /Organization/i }),
+          { target: { value: 'Test Org' } }
+        );
+      });
+      await act(() => {
+        fireEvent.change(screen.getByRole('textbox', { name: /Department/i }), {
+          target: { value: 'Test Dept' },
+        });
+      });
+      await act(() => {
+        fireEvent.submit(screen.getByTestId('accountinfoform'));
+      });
+
+      expect(
+        screen.getByText(/may contain only lowercase letters/i)
+      ).toBeInTheDocument();
+      expect(mockNavigate).not.toHaveBeenCalledWith('/signup/3');
+    }
+  );
 });
diff --git a/src/features/signup/AccountInformation.tsx b/src/features/signup/AccountInformation.tsx
index 156bd49a..6aeeefaf 100644
--- a/src/features/signup/AccountInformation.tsx
+++ b/src/features/signup/AccountInformation.tsx
@@ -58,8 +58,14 @@ export const AccountInformation: FC<{}> = () => {
   const [username, setUsername] = useState(account.username ?? '');
   const userAvail = loginUsernameSuggest.useQuery(username);
   const nameShort = username.length < 3;
-  const nameAvail =
-    userAvail.currentData?.availablename === username.toLowerCase();
+  const nameTooLong = username.length > 100;
+  // Mirrors backend rules in kbase/auth2 NewUserName: must start with a
+  // lowercase letter; only [a-z0-9_]; no repeating or trailing underscores.
+  const nameFormatValid =
+    /^[a-z][a-z0-9_]*$/.test(username) &&
+    !username.includes('__') &&
+    !username.endsWith('_');
+  const nameAvail = userAvail.currentData?.availablename === username;
 
   const surveyQuestion = 'How did you hear about us? (select all that apply)';
   const [optionalText, setOptionalText] = useState<Record<string, string>>({});
@@ -199,7 +205,11 @@ export const AccountInformation: FC<{}> = () => {
                   required: true,
                   onChange: (e) => setUsername(e.currentTarget.value),
                   validate: () =>
-                    !nameShort && !userAvail.isFetching && nameAvail,
+                    !nameShort &&
+                    !nameTooLong &&
+                    nameFormatValid &&
+                    !userAvail.isFetching &&
+                    nameAvail,
                 })}
                 defaultValue={account.username}
                 helperText={
@@ -209,6 +219,24 @@ export const AccountInformation: FC<{}> = () => {
                         Username is too short.
                         <br />
                       </span>
+                    ) : nameTooLong ? (
+                      <span>
+                        Username must be at most 100 characters.
+                        <br />
+                      </span>
+                    ) : !nameFormatValid ? (
+                      <span>
+                        Username may contain only lowercase letters, digits, and
+                        underscores, and must start with a letter. Underscores
+                        cannot repeat or end the username.
+                        {userAvail.currentData?.availablename ? (
+                          <>
+                            {' '}
+                            Suggested: "{userAvail.currentData.availablename}".
+                          </>
+                        ) : null}
+                        <br />
+                      </span>
                     ) : !nameAvail && !userAvail.isFetching ? (
                       <span>
                         Username is not available. Suggested: "
@@ -224,7 +252,12 @@ export const AccountInformation: FC<{}> = () => {
                     </span>
                   </>
                 }
-                error={nameShort || (!userAvail.isFetching && !nameAvail)}
+                error={
+                  nameShort ||
+                  nameTooLong ||
+                  !nameFormatValid ||
+                  (!userAvail.isFetching && !nameAvail)
+                }
               />
             </FormControl>
             <FormControl>