How I Solved a Vercel Function Timeout While Building an AI Website Audit Tool

While building my AI-powered Website Audit Tool, I ran into a production issue that only appeared on a handful of unusually slow websites.

Most audit reports completed successfully.

A few didn't.

They consistently failed with a timeout.

At first, I blamed Vercel.

More specifically, I blamed what I believed was Vercel's famous 60-second serverless function limit.

It turned out I was chasing the wrong problem.

The actual culprit was hiding inside my own code, and fixing it taught me several lessons about Vercel Fluid Compute, maxDuration, application-level timeouts, and why blindly trusting old documentation—or even AI-generated advice—can send you down the wrong debugging path.

This article walks through the entire debugging journey, including the mistakes I made, the experiments that failed, and the final solution.

Try the application that uncovered this issue

The timeout described in this article occurred while generating real reports in my Free AI Website Audit Tool.

It analyzes websites using Google PageSpeed Insights, Lighthouse metrics, and AI-generated recommendations to produce business-friendly Website Growth Opportunity Reports.

🔗 Try the Free AI Website Audit Tool

This wasn't a demo project or a toy example—it was discovered while building and testing a real production application.

What You'll Learn

By the end of this article you'll understand:

• Why many developers still believe Vercel has a hard 60-second limit
• What Fluid Compute changed
• How to correctly configure maxDuration
• Why increasing maxDuration alone may not fix your timeout
• How AbortSignal.timeout() can silently override your server timeout
• How I diagnosed the issue using production logs
• Why reducing work is often better than increasing limits

The AI Website Audit Tool

The application itself is fairly straightforward.

A visitor enters a website URL.

Behind the scenes the application performs multiple operations before producing a downloadable audit report.

                User
                  │
                  ▼
      AI Website Audit Tool (Next.js)
                  │
                  ▼
      Vercel Serverless Function
                  │
                  ▼
   Google PageSpeed Insights API
                  │
                  ▼
      Lighthouse Processing
                  │
                  ▼
   AI Recommendation Generation
                  │
                  ▼
 Website Growth Opportunity Report

Unlike a simple API request, Google PageSpeed Insights first performs a complete Lighthouse analysis before returning results.

For fast websites, this usually isn't a problem.

For slower websites, however, Lighthouse itself can take significantly longer to finish.

Since my application has to wait for Google's response before generating the report, the execution time depends entirely on how long Lighthouse takes.

Most websites completed in under 20 seconds.

A handful took much longer.

Those were the ones exposing the problem.

Production Environment

For anyone trying to reproduce this issue, here's the exact environment.

Symptoms:

• Fast websites worked perfectly.
• Slow websites randomly failed.
• Only certain domains triggered the timeout.
• Local development rarely reproduced the issue.

Those last two points made debugging especially frustrating.

The First Production Failure

The issue didn't appear during development.

It wasn't caught by unit tests.

It wasn't caused by a deployment.

Instead, it appeared while testing the AI Website Audit Tool against dozens of real business websites.

Some reports generated perfectly.

Others consistently failed.

One particularly slow website triggered the following error.

TimeoutError: The operation was aborted due to timeout

AbortSignal.timeout()

Elapsed Time:
41.6 seconds

Request Cancelled

At that moment I immediately jumped to the conclusion most developers probably would.

"This must be Vercel's 60-second timeout."

It seemed logical.

The internet is full of articles mentioning Vercel's 60-second execution limit.

Stack Overflow answers mention it.

Older blog posts mention it.

Even AI coding assistants often reference it because it was true for years.

So I started optimizing the application to fit inside what I assumed was a fixed platform limit.

That assumption turned out to be wrong.

My Debugging Timeline

Real debugging is rarely a straight line.

Here's roughly how the investigation unfolded.

Notice something interesting.

Nearly two hours of debugging had nothing to do with writing code.

Most of it involved verifying assumptions.

That's often where the real engineering work happens.

The Assumption That Sent Me in the Wrong Direction

For years, Vercel's traditional Serverless Functions had relatively short execution limits.

That information spread everywhere.

Blog posts.

YouTube tutorials.

Stack Overflow answers.

GitHub discussions.

AI assistants trained on older information.

So naturally, when I saw a timeout, I assumed I had reached the platform limit.

I started asking questions like:

• Can I make Lighthouse faster?
• Can I split the request?
• Can I cache more aggressively?
• Should I move everything into background jobs?

Those are good optimization questions.

They just weren't solving the right problem.

Before spending another hour rewriting code, I decided to stop relying on memory and read the latest Vercel documentation.

That decision completely changed the direction of the investigation.

What Changed? Vercel Fluid Compute

The biggest surprise wasn't discovering a bug.

It was discovering that my understanding of Vercel's execution model was outdated.

Vercel introduced Fluid Compute, a newer execution model designed to improve resource utilization and support longer-running workloads.

One of the biggest changes was function execution duration.

Instead of the old assumptions many developers still quote, projects using Fluid Compute can support significantly longer execution times.

At that point I realized I wasn't necessarily hitting a hard platform ceiling at all.

Instead, I needed to verify:

1. Was Fluid Compute enabled?
2. What was my configured maxDuration?
3. Was something else terminating the request first?

Those questions turned out to be far more useful than asking how to squeeze everything under an arbitrary 60-second limit.

A Lesson About Engineering Assumptions

One lesson from this debugging session extends far beyond Vercel.

Technology changes quickly.

Platform limits change.

Framework APIs evolve.

Documentation gets updated.

Articles written two years ago may no longer reflect current behavior.

Even AI assistants can confidently repeat information that was once correct but has since changed.

That doesn't mean the advice is bad—it simply means cloud platforms evolve faster than static knowledge.

Whenever you're debugging infrastructure-related issues, it's worth asking:

"Am I solving today's problem using yesterday's assumptions?"

That single question saved me from spending hours optimizing code for a limitation that no longer existed.

Moving from Diagnosis to Implementation

Now that we have established that my original assumption was wrong—and the issue wasn't simply that "Vercel has a hard 60-second limit"—the next step was figuring out exactly where the timeout was actually occurring.

As it turns out, multiple timeout mechanisms can exist within a single request context. Understanding exactly which layer is firing makes all the difference when moving from a high-level diagnosis to a real production fix.

The Real Fix: maxDuration, AbortSignal.timeout(), and the Mistake That Actually Caused the Timeout

The first thing I checked was whether my function was actually allowed to run long enough.

Earlier, we established that my original assumption was wrong.

The issue wasn't simply "Vercel has a 60-second limit."

The next step was figuring out where the timeout was actually occurring.

As it turns out, multiple timeout mechanisms can exist in a single request.

Understanding which one is firing makes all the difference.

Step 1 — Verify Your Function Configuration

The first thing I checked was whether my function was actually allowed to run long enough.

If you're using the Next.js App Router, configuring the maximum execution time is straightforward.

export const maxDuration = 120;

That tells Vercel the function is allowed to run for up to 120 seconds, assuming your plan supports it.

For projects using other frameworks or older Next.js versions, the same configuration can be placed inside vercel.json.

{
  "functions": {
    "api/**/*.js": {
      "maxDuration": 120
    }
  }
}

After deploying this change, I expected the issue to disappear.

It didn't.

The function still failed.

That was my first clue that Vercel itself might not be the component terminating the request.

Step 2 — Read the Logs, Not Your Assumptions

Instead of making another code change, I added timing information around every significant operation.

Something as simple as this quickly narrows down the bottleneck.

const start = performance.now();

const response = await fetch(url);

console.log(`Completed in ${Math.round(performance.now() - start)} ms`);

I logged:

• Request start
• PageSpeed API call
• Response received
• AI analysis
• Report generation
• Total execution time

Very quickly a pattern emerged.

Everything after the Google PageSpeed request executed almost instantly.

Nearly all of the request time was spent waiting for Lighthouse.

That was expected.

The strange part was this:

The request wasn't reaching 120 seconds.

It wasn't even reaching 60 seconds.

It was failing much earlier.

That meant something else was cancelling the request.

Step 3 — The Hidden Timeout

After tracing every asynchronous call, I eventually found this line.

signal: AbortSignal.timeout(40000);

There it was.

A timeout I had completely forgotten about.

I had originally added it as a safety mechanism.

The idea was simple:

"If Google doesn't respond within 40 seconds, cancel the request."

It made perfect sense while developing.

But once I increased the server execution limit, that 40-second timeout became the new bottleneck.

The request was never reaching Vercel's limit.

My own code was cancelling it first.

Why Increasing maxDuration Didn't Help

This is probably the most important takeaway from the entire article.

There are multiple layers of timeouts.

Think of them like this.

Client Request
      │
      ▼
Vercel Function
      │
      ▼
fetch()
      │
      ▼
AbortSignal.timeout()
      │
      ▼
Google PageSpeed API

Increasing the outer timeout doesn't automatically increase the inner ones.

Imagine setting your function to 120 seconds.

Vercel Function
120 seconds

But inside that function you still have:

AbortSignal.timeout(40000)

The request will still stop after 40 seconds.

Not because Vercel stopped it.

Because your own application did.

The Fix

Once I found the real bottleneck, the fix was almost embarrassingly simple.

Before:

const response = await fetch(apiUrl, {
  signal: AbortSignal.timeout(40000),
});

After:

const response = await fetch(apiUrl, {
  signal: AbortSignal.timeout(100000),
});

Combined with:

export const maxDuration = 120;

The application immediately started completing reports that had previously failed.

Sometimes the hardest bugs don't require complicated solutions.

They require finding the correct layer.

Why Only Certain Websites Failed

One question still remained.

Why did most websites work perfectly?

The answer lies in Google PageSpeed Insights itself.

Lighthouse doesn't spend the same amount of time analyzing every website.

Some sites are lightweight.

Some are extremely heavy.

For example:

My AI Website Audit Tool waits for Google's Lighthouse analysis to finish before generating recommendations.

That means I don't control this part of the execution time.

The slower Google's analysis is, the longer my server function waits.

That's exactly why only a few websites exposed the issue.

The Better Optimization

Increasing the timeout solved the symptom.

Reducing unnecessary work improved the application.

Originally, my audit requested every Lighthouse category.

Performance
Accessibility
SEO
Best Practices

That isn't always necessary.

If your application only needs performance metrics, requesting fewer categories reduces the amount of work Google has to perform.

Less work means:

• Faster responses
• Lower server execution time
• Lower infrastructure costs
• Better user experience

Longer timeouts should be your safety net.

Not your first optimization strategy.

Another Real-World Gotcha

While researching this issue, I came across developers who had:

• Enabled Fluid Compute
• Increased maxDuration
• Configured higher limits in the Vercel dashboard

...and were still hitting 60-second timeouts.

The reason?

Certain route types or framework integrations may have their own execution behavior or separate configuration paths.

The important lesson is this:

If your function still times out after increasing every documented limit, don't immediately assume Vercel is ignoring your configuration.

Instead, ask:

• Is this really a standard API route?
• Is another library enforcing its own timeout?
• Is a proxy terminating the request?
• Is the external API itself closing the connection?
• Am I cancelling the request somewhere else?

Always verify where the timeout originates before changing infrastructure settings.

My Before vs After

Here's what actually changed.

Interestingly, increasing the timeout wasn't even the biggest improvement.

The detailed logging was.

Once every operation had timestamps, the problem almost revealed itself.

Lessons Learned

Looking back, there were several important engineering lessons.

1. Verify assumptions first

Most of my debugging time wasn't spent fixing code.

It was spent challenging assumptions.

2. Infrastructure changes over time

Cloud platforms evolve constantly.

Limits that were true two years ago may no longer exist.

Always verify current documentation.

3. AI is a great assistant—not an authority

I used AI during this debugging session.

It was incredibly useful for brainstorming and reviewing code.

But it also initially treated the old 60-second limit as a fixed constraint because that information had been widely repeated for years.

That wasn't an AI failure.

It was a reminder that platform-specific behavior changes over time, and the official documentation should always be the final reference.

4. Every timeout has an owner

When a request fails, ask:

Who actually cancelled this request?

The answer might be:

• Your code
• Your framework
• Your hosting platform
• A reverse proxy
• A load balancer
• The external API

Finding the owner is often more valuable than increasing every timeout value.

5. Better logging beats better guessing

Adding timing information around every asynchronous operation solved this bug faster than any optimization attempt.

Logs don't make assumptions.

Developers do.

Quick Debugging Checklist

If you're facing a Vercel Function Timeout, here's the checklist I wish I'd followed from the beginning.

✅ Verify maxDuration

✅ Confirm Fluid Compute is enabled

✅ Read the latest Vercel documentation

✅ Add timing logs around every external API call

✅ Check AbortSignal.timeout()

✅ Check Axios or fetch timeout settings

✅ Review proxy and CDN timeouts

✅ Optimize the amount of work instead of only increasing limits

FAQ: Troubleshooting Vercel Function Timeouts

How do I increase Vercel function timeout?

To increase the execution limit of your Vercel functions, you can configure the maxDuration property. Depending on your framework and project setup, you can do this in two ways:

1. Next.js App Router (Route-level configuration): Export a maxDuration constant directly from your API route or page file:

   export const maxDuration = 120; // set limit to 120 seconds
   

   Copy
2. Vercel Configuration File (vercel.json): Define the duration globally or for specific patterns in the functions property:

   {
     "functions": {
       "api/**/*.js": {
         "maxDuration": 120
       }
     }
   }
   

   Copy

Note: The maximum allowable limit depends on your Vercel plan (Hobby: 10s, Pro: up to 300s, Enterprise: up to 900s).

Why does my Vercel function still timeout after increasing maxDuration?

If you've successfully increased Vercel's maxDuration in your configuration, but still experience a 504 Gateway Timeout or an aborted request, the issue lies in one of the following layers:

1. Application-level Fetch Timeouts: Look for AbortSignal.timeout(ms) or third-party HTTP client options (like Axios's timeout option) that abort the request early.
2. Database Query Timeouts: Some database clients have separate connection and query timeout settings (e.g., Prisma or pg pool configurations) that default to 30 seconds.
3. External API Boundaries: The third-party API you are calling might be terminating the connection on their end, or they might take too long to start streaming the response back.
4. Platform Execution Limits: If you are on a Vercel Hobby plan, the hard maximum limit is 10 seconds regardless of what you set maxDuration to. Ensure you are on a Pro or Enterprise plan if you need larger limits.

Final Thoughts

What started as a seemingly simple timeout turned into a useful reminder about modern cloud development.

The bug wasn't caused by Vercel.

It wasn't caused by Next.js.

It wasn't even caused by Google PageSpeed Insights.

It was caused by a forgotten timeout configuration inside my own application—combined with an outdated assumption about how Vercel functions work today.

Once I increased the function's execution limit, updated the application's own timeout, and reduced unnecessary work, the AI Website Audit Tool began generating reports reliably, even for websites that had previously failed.

Sometimes the best debugging technique isn't writing more code.

It's asking whether you're solving the right problem.

Try the AI Website Audit Tool

The production issue described in this article was discovered while building my Free AI Website Audit Tool.

It analyzes websites using Google PageSpeed Insights and AI-generated recommendations to produce detailed Website Growth Opportunity Reports covering:

• Performance
• SEO
• Accessibility
• Best Practices
• Technical Foundation
• AI Search Readiness
• Trust & Credibility
• Actionable improvement recommendations

🔗 Try the Free AI Website Audit Tool

If you're building with Next.js, Vercel, or integrating external APIs like Google PageSpeed Insights and are facing similar production issues, I hope this debugging journey saves you a few hours—and perhaps a few incorrect assumptions.

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• Google's New PageSpeed Agentic Browsing Score: Why Your Website May Be Invisible to AI
• How to Analyze Your Google Analytics Data with AI: GA4 AI Agent Guide
• WordPress PageSpeed Optimization: How We Improved Mobile Performance from 56 to 98

About the Author

Hi, I'm Naveen Gaur, a Full-Stack Developer specializing in Next.js, React, Node.js, WordPress, SEO, and AI-powered web applications.

I enjoy building practical tools that solve real business problems—from AI-powered Website Audit platforms to custom web applications and automation workflows. Whenever I encounter an interesting engineering challenge in production, I document the debugging process so others can learn from it too.