diff --git a/apps/mobile/src/features/projects/AddProjectScreen.tsx b/apps/mobile/src/features/projects/AddProjectScreen.tsx
index 0b079d9902ad..15be20b2a206 100644
--- a/apps/mobile/src/features/projects/AddProjectScreen.tsx
+++ b/apps/mobile/src/features/projects/AddProjectScreen.tsx
@@ -18,6 +18,7 @@ import {
   getNewProjectGitHubRepository,
   getNewProjectGitHubTarget,
   getNewProjectPathPreview,
+  githubIncompleteOwnerRepositoryMessage,
   normalizePastedCloneUrl,
   resolveAddProjectPath,
   sortAddProjectProviderSources,
@@ -755,6 +756,11 @@ export function AddProjectRepositoryScreen(props: {
 
   const lookupRepository = useCallback(async () => {
     if (!environment || repositoryInput.trim().length === 0 || isSubmitting) return;
+    const incompleteOwnerMessage = githubIncompleteOwnerRepositoryMessage(source, repositoryInput);
+    if (incompleteOwnerMessage) {
+      setError(incompleteOwnerMessage);
+      return;
+    }
     setError(null);
     setIsSubmitting(true);
     const provider = addProjectRemoteSourceProvider(source);
diff --git a/apps/web/src/components/CommandPalette.tsx b/apps/web/src/components/CommandPalette.tsx
index f7b78b5ae676..e88c2c766750 100644
--- a/apps/web/src/components/CommandPalette.tsx
+++ b/apps/web/src/components/CommandPalette.tsx
@@ -13,6 +13,7 @@ import {
   getNewProjectGitHubRepository,
   getNewProjectGitHubTarget,
   getNewProjectPathPreview,
+  githubIncompleteOwnerRepositoryMessage,
   normalizePastedCloneUrl,
 } from "@t3tools/client-runtime/operations/projects";
 import { connectionStatusText } from "@t3tools/client-runtime/connection";
@@ -2561,6 +2562,21 @@ function OpenCommandPaletteDialog(props: {
         return;
       }
 
+      const incompleteOwnerMessage = githubIncompleteOwnerRepositoryMessage(
+        addProjectCloneFlow.source,
+        rawRepository,
+      );
+      if (incompleteOwnerMessage) {
+        toastManager.add(
+          stackedThreadToast({
+            type: "error",
+            title: "Repository name incomplete",
+            description: incompleteOwnerMessage,
+          }),
+        );
+        return;
+      }
+
       const provider = remoteProjectSourceProvider(addProjectCloneFlow.source);
       if (!provider) {
         const destinationPath = getCloneDestinationPath(
diff --git a/packages/client-runtime/src/operations/projects.test.ts b/packages/client-runtime/src/operations/projects.test.ts
index 9343e9842056..b46a3fee2eb1 100644
--- a/packages/client-runtime/src/operations/projects.test.ts
+++ b/packages/client-runtime/src/operations/projects.test.ts
@@ -17,6 +17,7 @@ import {
   getCloneDestinationPath,
   getCloneDirectoryName,
   getDefaultCloneUrl,
+  githubIncompleteOwnerRepositoryMessage,
   normalizePastedCloneUrl,
   resolveAddProjectPath,
   sortAddProjectProviderSources,
@@ -24,6 +25,27 @@ import {
 import type { EnvironmentProject } from "../state/models.ts";
 
 describe("add project shared logic", () => {
+  it("asks for a repository name when GitHub input is only an owner path", () => {
+    expect(githubIncompleteOwnerRepositoryMessage("github", "pingdotgg/")).toBe(
+      "Enter the full owner/repository name.",
+    );
+    expect(githubIncompleteOwnerRepositoryMessage("github", "  pingdotgg//  ")).toBe(
+      "Enter the full owner/repository name.",
+    );
+
+    for (const input of [
+      "pingdotgg/t3code",
+      "pingdotgg",
+      "https://github.com/pingdotgg/t3code.git",
+      "git@github.com:pingdotgg/t3code.git",
+    ]) {
+      expect(githubIncompleteOwnerRepositoryMessage("github", input)).toBeNull();
+    }
+    expect(githubIncompleteOwnerRepositoryMessage("gitlab", "group/")).toBeNull();
+    expect(githubIncompleteOwnerRepositoryMessage("url", "owner/")).toBeNull();
+    expect(githubIncompleteOwnerRepositoryMessage("forgejo", "owner/")).toBeNull();
+  });
+
   it("only allows project creation in connected environments", () => {
     expect(canCreateProjectInEnvironment("connected")).toBe(true);
     expect(canCreateProjectInEnvironment("available")).toBe(false);
diff --git a/packages/client-runtime/src/operations/projects.ts b/packages/client-runtime/src/operations/projects.ts
index 8dd937d3a68d..b2533e340b6f 100644
--- a/packages/client-runtime/src/operations/projects.ts
+++ b/packages/client-runtime/src/operations/projects.ts
@@ -129,6 +129,25 @@ export function addProjectRemoteSourceProvider(
 const GITHUB_REPOSITORY_SHORTHAND =
   /^[A-Za-z0-9](?:[A-Za-z0-9-]{0,38})\/[A-Za-z0-9._-]+(?:\.git)?$/;
 
+/** Owner present, repository name missing: `owner/` or `owner//`. */
+const INCOMPLETE_GITHUB_OWNER_PATH = /^[A-Za-z0-9](?:[A-Za-z0-9-]{0,38})\/+$/;
+
+const INCOMPLETE_GITHUB_OWNER_REPOSITORY_MESSAGE = "Enter the full owner/repository name.";
+
+/**
+ * Message to show when a GitHub add-project field is only `owner/`.
+ * Lookup would send that to GitHub and come back as a generic failure.
+ * Returns null for complete names, bare repo names, URLs, and other sources.
+ */
+export function githubIncompleteOwnerRepositoryMessage(
+  source: AddProjectRemoteSource,
+  input: string,
+): string | null {
+  if (source !== "github") return null;
+  if (!INCOMPLETE_GITHUB_OWNER_PATH.test(input.trim())) return null;
+  return INCOMPLETE_GITHUB_OWNER_REPOSITORY_MESSAGE;
+}
+
 /** Treat the common owner/repository shorthand as a public GitHub HTTPS URL. */
 export function normalizePastedCloneUrl(input: string): string {
   const trimmed = input.trim();