Test Your AI Skills

Mar 1, 2026

The Race Condition In The Payment Flow

~2% of customers are being charged twice. Your payment flow: frontend POSTs to `/api/charge`, backend creates a Stripe PaymentIntent, returns clien...

Feb 22, 2026

The Overflowing Grid

A developer is building a puzzle platform. One puzzle page shows a **two-column layout**: a wide main content area on the left and a sticky sidebar...

Feb 21, 2026

The ENV That Disappears At Build Time

Your Next.js app uses `NEXT_PUBLIC_API_URL` in the browser. Works in dev. In production on Vercel, it's `undefined`. You've set it in Vercel's dash...

Feb 20, 2026

The Cascading Delete That Wasn't

You delete a user. No error. But their orders, reviews, and sessions are still in the database — completely orphaned. The Rails migration clearly s...

Feb 19, 2026

Webpack Bundle: The 4MB Surprise

Your production bundle is 4.2MB. Budget is 500KB. The bundle analyzer reveals that 67% of it is `aws-sdk` — all 2.8MB. Nobody on your team uses AWS...

Feb 18, 2026

The API Key That Works In Postman

Your API key works in Postman. Curl works too. Your React app gets 403 Forbidden. Same key, same endpoint. The Network tab shows... wait, it shows ...

Feb 17, 2026

The Docker Build That Works On My Mac

Your Dockerfile builds perfectly on your M2 Mac. GitHub Actions (ubuntu, x86_64) fails during `npm ci` with a native module compilation error. The ...

Feb 16, 2026

The SQL Join That Inflates Totals

Your customer report query returns correct row counts after GROUP BY, but the `SUM(o.amount)` values are wildly inflated. A customer who spent $500...

Feb 15, 2026

OAuth Redirect URI — The Trailing Slash

Google OAuth login broke after deploying to staging. Error: `redirect_uri_mismatch`. You've added the staging URL to Google Cloud Console. You've t...

Feb 14, 2026

The Migration That Locks The Table

Your Rails migration adds a column with a default value to a table with 12 million rows. Postgres 11+ handles this instantly — no table rewrite nee...

Feb 13, 2026

The Phantom 301 Redirect Loop

Your team migrated from HTTP to HTTPS. The site now redirect-loops infinitely — Chrome shows `ERR_TOO_MANY_REDIRECTS`. You're behind Cloudflare wit...

Feb 12, 2026

N+1 Query From a Single Endpoint

Your `/api/teams` endpoint takes 12 seconds to load. There are only 45 teams. Your Prisma ORM generates efficient `IN` queries for the `include` re...

Feb 11, 2026

The 200 OK That's Actually An Error

Your frontend POSTs to `/api/subscribe` and gets 200 OK. The UI shows "Subscribed! 🎉" But users never receive emails. Turns out the backend always...

Feb 10, 2026

The Rebase That Ate Three Commits

You ran an interactive rebase to clean up your feature branch before merging. After the rebase and force-push, three commits are missing — includin...

Feb 9, 2026

GitHub Actions: The Secret That Isn't

Your CI deploy step suddenly fails. The error says AWS credentials are empty. You check GitHub Secrets — they're there. The workflow file hasn't ch...

Feb 8, 2026

The WHERE Clause That Ate Production

A PM ran a quick SQL update to fix a typo in one company's name. Instead of updating 1 row, it updated all 4,847 rows in the `organizations` table....

Feb 7, 2026

JWT Expired But The Clock Is Fine

Your app's auth breaks for ~30% of users. They log in, get a JWT, and within seconds get 401 Unauthorized. The JWT has a 1-hour expiry. Your backen...

Feb 6, 2026

The CSS Grid That Breaks On Safari

Your product grid looks perfect on Chrome. On Safari (including all iPhones), the grid item images collapse to zero height. Your PM tests on their ...

Feb 5, 2026

Z-Index War: The Modal That Hides

You added a confirmation modal to your app. It works great in isolation, but when triggered from the sidebar, it renders *behind* the sidebar. You'...

Feb 4, 2026

CORS From Hell — The Preflight Mystery

You're building a React dashboard that calls your company's internal API. GET requests work perfectly. But the moment you try to POST a new record,...