Error tracking for TanStack Start, in the browser and on the server

The short answer#

• One package, @belvador/tanstack-start, wired in the router, the server entry and the middleware.

• It reports browser errors, route error boundaries, and server function and server route failures on Workers.

• It works for apps built with Lovable, which are TanStack Start apps on Cloudflare Workers.

• Redirects, notFound(), status codes below 500 and cancelled requests are not reported.

Three places, one package#

Each part reports what the others miss, so the guide wires all three (TanStack Start guide).

Install#

npm install @belvador/tanstack-start@0.6.1

Router#

import { init } from "@belvador/tanstack-start/client";// Imported first by src/start.ts and src/router.tsx. Runs only in the browser.if (typeof window !== "undefined") {  init({    dsn: "https://<public-key>@ingest.belvador.dev/<project-id>",    release: import.meta.env.VITE_APP_VERSION, // your build or commit id    environment: import.meta.env.MODE,  });}

import "./instrument"; // first line, before the route treeimport { withBelvadorRouter } from "@belvador/tanstack-start/client";// In getRouter(): wrap the options you already pass to createRouter.// createRouter(withBelvadorRouter({ routeTree, ...yourOptions }))// It reports route errors, calls your own defaultOnCatch after that, and adds// TanStack's error component only if you set no defaultErrorComponent.

Server entry#

import handler from "@tanstack/react-start/server-entry";import { withBelvador } from "@belvador/tanstack-start/server";// Requires Cloudflare Workers with nodejs_compat enabled.// If src/server.ts already exists, wrap its default export instead of `handler`.// vite.config.ts needs tanstackStart: { server: { entry: "server" } } (Lovable apps have it).export default withBelvador(  (env: { BELVADOR_DSN?: string; BELVADOR_RELEASE?: string }) => ({    dsn: env.BELVADOR_DSN ?? "https://<public-key>@ingest.belvador.dev/<project-id>",    release: env.BELVADOR_RELEASE,  }),  handler,);

The middleware step and the Content Security Policy line are in the guide. Keep what your app already does: add to an existing src/server.ts or src/start.ts, do not replace them.

Requirements#

• @tanstack/react-router and @tanstack/react-start 1.168 or newer, React 18 or 19.

• Cloudflare Workers with the nodejs_compat flag. Lovable apps already have it.

More than errors#

• Cron jobs in the same app can report check-ins with withMonitor() (cron monitoring).

• Traces and logs go through the standard OpenTelemetry exporter (OpenTelemetry for TanStack Start).

• An AI agent prompt in the guide sets the package up in Lovable or another coding agent.

Limits#

• Redirects, notFound(), errors with a status below 500 (499 included) and requests the visitor cancelled are not reported — they are not bugs.

• An error thrown in a route loader while the page renders on the server is usually reported from the browser, without the server stack. Server functions called from loaders keep their server stack.

• No replay and no browser tracing.

• Server code that runs outside Belvador's middleware is reported as a connection problem on the project, so you can find it (connection problems).

Questions#

Does this work on Node.js hosting instead of Workers?#

The server half is built and tested for Cloudflare Workers. On another runtime, use the browser part and the Node.js setup for the server.