remix-run/react-router · error

Unable to define routes with duplicate route id

Error message

Unable to define routes with duplicate route id: "${route.id}"

What it means

defineRoutes keys its manifest by route id, which defaults to createRouteId(file) — the module's file path — or an explicit options.id. Before inserting, it checks 'route.id in routes' and throws on a collision rather than letting the second definition silently overwrite the first. This guards against ambiguous route trees where two entries claim the same id.

Solutions

1. Give each route a unique file path
2. When intentionally reusing a module, pass distinct id options: route('a', 'page.tsx', { id: 'a' }) and route('b', 'page.tsx', { id: 'b' })
3. Check for accidental duplicates in generated/looped route definitions

Example fix

// before
const routes = defineRoutes(() => {
  route("about", "routes/page.tsx");
  route("company", "routes/page.tsx"); // same file => duplicate id
});

// after
const routes = defineRoutes(() => {
  route("about", "routes/page.tsx", { id: "about-page" });
  route("company", "routes/page.tsx", { id: "company-page" });
});

// track ids yourself and fail with a clearer message before the library does
const seen = new Set<string>();
function assertUniqueId(id: string) {
  if (seen.has(id)) throw new Error(`Duplicate route id: '${id}'`);
  seen.add(id);
}
const routes = defineRoutes(() => {
  assertUniqueId("about-page");
  route("about", "routes/page.tsx", { id: "about-page" });
  assertUniqueId("company-page");
  route("company", "routes/page.tsx", { id: "company-page" });
});

When it happens

Trigger: Two route() calls referencing the same file path (same derived id); two calls passing the same explicit id option; a helper loop generating definitions that collapse onto one file or id.

Common situations: Copy-pasted route definitions reusing a file; mapping a list where multiple entries render the same component file; deliberately using one module for both a pathless layout and a page without giving one a distinct id.

Related errors

• You tried to define routes asynchronously but started…
• Expected a route.id in react-router processRoutes() function

AI-assisted analysis of remix-run/react-router@6beaca3952 (2026-08-18). Data as JSON: /api/errors/b6f131d3fb9296f7. Report an issue: GitHub.

Appendix: source

Thrown at packages/react-router-remix-routes-option-adapter/defineRoutes.ts:103

      // route(path, file, options, children)
      // route(path, file, options)
      options = optionsOrChildren || {};
    }

    let route: RouteManifestEntry = {
      path: path ? path : undefined,
      index: options.index ? true : undefined,
      caseSensitive: options.caseSensitive ? true : undefined,
      id: options.id || createRouteId(file),
      parentId:
        parentRoutes.length > 0
          ? parentRoutes[parentRoutes.length - 1].id
          : "root",
      file,
    };

    if (route.id in routes) {
      throw new Error(
        `Unable to define routes with duplicate route id: "${route.id}"`,
      );
    }

    routes[route.id] = route;

    if (children) {
      parentRoutes.push(route);
      children();
      parentRoutes.pop();
    }
  };

  callback(defineRoute);

  alreadyReturned = true;

  return routes;

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