Tanstack start + nitro (with basePath) infinite redirect for url parameter with dots

[Julienng]

Which project does this relate to?

Start

Describe the bug

Hi,

I'm facing an infinite redirect in Dev and Prod for a specific config of Tanstack Start + Nitro.

The problem occurs when:

• A splat route is used as a proxy, and the URL looks like this: /subdir/api/proxy/todos/Package.todos.Entity.1
• Vite config is setting a basePath

The config:

const config = defineConfig({
  base: "/subdir",
  plugins: [
    devtools(),
    nitro({ baseURL: "/subdir" }),
    tsconfigPaths({ projects: ["./tsconfig.json"] }),
    tailwindcss(),
    tanstackStart(),
    viteReact(),
  ],
});

Your Example Website or App

https://github.com/Julienng/tanstack-nitro-basepath-id-with-dots-reproduction-bug

Steps to Reproduce the Bug or Issue

1. Go to the index page: http://localhost:3000/subdir/
2. Choose one of the 3 detail pages and open
3. An infinite redirect occurs, and the error page is shown
4. Refresh browser -> the page is shown properly (the page and resource are accessible, but proxy from frontend is bugged)

Expected behavior

The call to /api/proxy/$ should not do an infinite redirect

Screenshots or Videos

Screen.Recording.2026-03-12.at.13.46.33.mov

Platform

• Router Start Version: latest (setted by cli)
• Nitro: 3.0.260311-beta (problem is present in alpha too)
• OS: Macos 26.2
• Browser: Chrome
• Browser Version: 144.0.7559.133
• Bundler: vite
• Bundler Version: ^7.3.1

Additional context

When Nitro is disabled, Tanstack routing is resolving the route correctly