Is my v0 app secure? The Next.js gaps v0 tends to leave

What are the common security gaps in a v0 app?

The common v0 gaps all sit on the boundary between what runs in the browser and what runs on the server. v0 is excellent at generating a good-looking Next.js UI quickly, but it tends to skip the server-side hardening: authentication on API routes, validation of incoming data, and careful handling of which environment variables reach the client.

In Next.js, code runs in two places. The server (API routes, Server Components, middleware) sees all your environment variables and should be where security lives. The browser only sees variables prefixed with NEXT_PUBLIC_, and anything it sees, an attacker sees. The two most common v0 flaws each come from getting this boundary wrong.

Flaw 1: API routes with no authentication

The most common v0 flaw is an API route that does its job, fetch data, update a record, but never checks who's asking. v0 generates working handlers and rarely adds auth. In the Next.js App Router, API routes are just files, so an attacker can guess common paths like /api/users, /api/admin, or /api/settings and hit them directly.

Here's the shape Explain My Build points at, cited to your route file:

// app/api/users/route.ts
export async function GET() {
  // No session check, no auth. Anyone who hits this URL
  // gets the data.
  const users = await db.users.findMany();
  return Response.json(users);
}

The same applies to Server Actions: they create discoverable server references, so you must treat every Server Action as a public endpoint and validate the session inside it. The fix: add an auth/session check at the top of every route and action that touches real data, and validate the incoming payload (a schema library like Zod is the common choice). Explain My Build lists every unprotected route in your app.

Flaw 2: Secrets leaking through NEXT_PUBLIC_

The second flaw is a secret exposed through the NEXT_PUBLIC_ prefix. Any variable named NEXT_PUBLIC_SOMETHING gets baked into the JavaScript bundle sent to every visitor's browser. That's correct for public values (an analytics ID, a public CDN URL), but a disaster for a database URL, a private API key, a JWT secret, or an OAuth client secret.

It's an easy mistake: naming a variable NEXT_PUBLIC_API_KEY to "make it work" on the client quietly ships that key to the world. Explain My Build reads your env usage and flags any sensitive value exposed this way, cited to the file.

The fix: keep secrets as plain server-only variables (no NEXT_PUBLIC_ prefix) and use them only in server code. If the browser needs data derived from a secret, have a server route produce it and return only the safe result. Our environment variable glossary entry spells out which values are safe to expose.

Why does v0 leave these gaps?

v0 leaves these gaps because its job is to turn a prompt into a beautiful, working interface, and it does that job well. Auth checks, input validation, and the careful server/client split are invisible in the preview, so they're the parts most likely to be skipped. That's not a knock on v0's UI work; it's just the shape of a tool optimised for front-end speed.

The practical consequence for a non-technical founder is that your app can look finished and demo perfectly while every API route is wide open. You can't see that in the browser, you can only see it in the code. Explain My Build reads the code and surfaces exactly where the server boundary is missing.

What you get for your v0 app

Point Explain My Build at your repo (run it locally so nothing leaves your machine, or paste a public URL that's read then deleted) and you get, each cited to your code:

• A plain-English list of every unprotected API route and every secret exposed via NEXT_PUBLIC_.
• A ranked, code-verified fix-list to hand your AI, e.g. "add a session check to this route; move this key off the public prefix."
• A founder runbook that maps your app's server and client boundary.

The runbook and fix-list are free. The shareable end-user guide is $19/month (or $12/month founding for the first 100), see pricing. Start by documenting your v0 app to see every route that needs a check.