My dashboard was taking 47 seconds to load. Turns out i was making 600 database queries without knowing it

helpdevtools — Sat, 21 Mar 2026 14:23:30 +0000

i was building a simple dashboard. nothing fancy.
just fetch some user data and display it.

opened it to test something and just stared at
my screen for almost a minute. 47 seconds to load.
for 200 users.

first i did what every developer does. checked the
network tab. refreshed 3 times. blamed my wifi.
still 47 seconds.

so i stopped guessing and used an AI prompt to
find the problem.

here's the prompt i used:

"Act as a performance engineer. This code is running
slower than expected. The app loads a dashboard that
fetches user data. With 100 users it loads in 200ms.
With 10,000 users it takes 45 seconds and sometimes
crashes. Identify the bottleneck, explain why it's
slow, and rewrite an optimized version with comments
on what changed."

the response was not what i expected.

i was making 3 separate database calls inside a loop.
one for the profile, one for orders, one for last
login. per user. every single time someone opened
the dashboard.

sounds fine when you write it. its not fine when
you do the math.

200 users = 600 queries. 10,000 users = 30,000 queries.

it has a name apparently. the N+1 query problem. one
of the most common performance bugs in backend
development and i had genuinely never heard of it.

the before and after is kind of embarrassing:

45 seconds to 200ms. the fix replaced the loop with
3 parallel bulk queries using Promise.all. instead of
hitting the database once per user it fetches
everything in one shot for all users at once.

6 changes. maybe 20 minutes to implement.

the thing that got me is this code looked completely
normal. readable. clean even. no red flags. it just
happened to be silently destroying performance at
any kind of scale.

i would have never found this by staring at the code.
i had been looking at it for days.

lesson: working code and fast code are not the same thing.

going to keep running these prompts on the rest of
the codebase. slightly terrified of what else i'll find.

if you want to try this on your own code just copy
the prompt above and paste your actual function
instead of mine. i have 99 more prompts like this
organized by category here 👉 https://payhip.com/b/i7IZa

I Was Stuck on a JWT Bug for 2 Hours. This AI Prompt Found the Root Cause in Seconds.

helpdevtools — Fri, 20 Mar 2026 10:07:54 +0000

We've all been there.

A bug with zero console errors. No obvious
cause. Just broken behavior that makes
absolutely no sense.

My JWT token was storing correctly after
login — I could see it in localStorage.
But after every single page refresh, the
user was logged out and the token was gone.

Silent failure. Nothing in the logs.
Hours wasted.

The Prompt That Fixed It

Instead of googling for the 100th time,
I used this structured AI prompt:

"You are a world-class debugger.
I have a bug I cannot solve.

What the code should do: authenticate a
user with JWT, store the token in
localStorage, and keep them logged in
after page refresh.

What it actually does: user logs in
successfully, token is stored, but after
page refresh the user is logged out and
the token disappears from localStorage.

Error: no error in console.

Code: `// Login function
async function loginUser(email, password) {
const response = await fetch('/api/auth/login', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({ email, password })
});
const data = await response.json();
localStorage.setItem('token', data.token);
window.location.href = '/dashboard';
}

// Check auth on page load
window.onload = function() {
const token = localStorage.getItem('token');
if (!token) {
window.location.href = '/login';
}
}
`
What I've tried: console.log before
setItem confirms token exists, but after
redirect it's gone.

Think step by step and solve it."

What Happened Next

Claude immediately identified the root cause:

Then gave a complete step by step diagnosis:

And a full working fix with comments:

The Root Cause

The culprit was a race condition between
localStorage.setItem and
window.location.href.

The redirect fires before the browser
finishes writing to localStorage. The page
tears down mid-write and the token silently
vanishes. No error. No warning.

I never would have thought of that.

Why This Prompt Works So Well

Most developers ask AI vague questions like
"why is my localStorage not working?" and
get generic answers.

This prompt works because it forces you to
give the AI everything it needs:

What the code SHOULD do
What it ACTUALLY does
The exact error
The exact code
What you already tried

The more context you give, the more
surgical the diagnosis.

Want More Prompts Like This?

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specifically for developers — organized into
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Debugging (15 prompts)
Code Generation (15 prompts)
Security & Code Review (10 prompts)
Testing (10 prompts)
DevOps & Deployment (10 prompts)
Documentation (10 prompts)
Career & Interviews (10 prompts)
Productivity (20 prompts)

Each prompt includes:
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Drop any questions in the comments — happy
to share more examples.