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Test your Next.js app the way users will use it
A Next.js build can pass type checks and unit tests and still break in the browser: a hydration error, a server action that fails in production, a middleware redirect that loops. Here is how to catch those on every preview.
How do I test a Next.js app before it ships?
Run your unit and type checks, then use the deployed preview the way a user would. Mimiq sends AI agents through the preview in real browsers: they report where they got stuck, and the browser records console errors such as hydration failures, server actions or API routes that answer 4xx or 5xx, and requests slower than 3 seconds, on the step each happened.
Where Next.js apps break for users
The failures that matter happen between server and browser: markup that does not match on the client, a server action that throws only with production environment variables, an edge middleware redirect that sends signed-out users in a circle, a route handler that times out on the first cold start. None of them shows in next build. All of them show to the first user.
- Console errors from your own code, such as hydration mismatches.
- Server actions and route handlers that answer 4xx or 5xx, with method and path.
- Requests slower than 3 seconds, such as a cold route handler.
- Redirect loops and dead ends, as the agent saw them.
- Runs on Vercel previews, including protected ones.
How it works
- 01
Give it a link and a task
A preview, staging or the live app, and a task in plain words like "Sign up and start using it". No test scripts.
- 02
Agents use it
5 agents by default, each acting as a different one of your users in its own real browser, with a working inbox for verification emails.
- 03
Read what they hit
What broke, what the browser recorded (JavaScript errors, failed and slow requests), where each agent got stuck and why, with a screenshot of every step.
- 04
Fix and rerun
Run the same agents on the fixed build, by hand, from your coding agent, or on every preview deploy with the GitHub Action.
What the browser records
Page loads, fetches and server action calls to your own domain: a 4xx or 5xx answer, a failed request, or an answer that took more than 3 seconds. Uncaught exceptions and console errors from your own scripts, with the message cut short and anything that looks like a token or an email masked. Third-party scripts are left out. Each record sits on the step it happened, next to the screenshot and the agent's words.
On every pull request
Most Next.js apps deploy previews on Vercel. The GitHub Action runs on each preview and keeps one comment on the pull request; with Deployment Protection on, pass your bypass secret. See the Vercel page for the workflow.
Limits
Agents are simulated users. They find problems fast and on every build; they do not forecast how many real people will convert, they are not a deterministic regression suite, and they do not install native mobile apps.
Image optimization and static asset requests are not recorded; only page loads, fetches and server calls are.
Questions
Does it work with the App Router and the Pages Router?
Yes. Agents use the rendered app in a browser; how the routes are built does not matter to them.
Can it test pages behind NextAuth or Clerk?
With paid credits, agents can sign in with a test account you give them and open protected previews (a Vercel bypass secret or a site password). The secrets are filled in only in the browser and deleted when the run ends. Test accounts and protected previews come with paid credits: the $9 Starter or a plan from $19 a month.
What does a check cost?
5 credits an agent. Your first test is free with a free account: sign in with Google and it starts right away, no card. The account includes 50 credits, enough for 10 agents. After that an agent uses 5 credits, and then it is a $9 Starter (120 credits that never expire) or monthly plans from $19.
Keep reading
Let the agents find what breaks first.
Your first test is free: sign in with Google and it starts right away. Last checked 2026-10-22.