The Codikko blog
Short, visual explainers for the ideas that trip up self taught developers. Step through each one, then go deeper in the lesson it comes from.
20 things AI leaves out of the login it built you
The gaps AI leaves in auth, from email verification to password reset and sessions, each with a copy-ready prompt and a browser check that proves it works.
Your AI agent is stuck in a loop: 12 prompts that break it
Twelve copy-ready prompts for when your AI agent keeps saying it fixed the bug and ships the same fix, cheapest first, each with a way to tell it worked.
12 security holes AI leaves in your app, and how to close them
A copy-ready prompt to close each of the twelve security holes AI leaves in most apps, and a browser check under each one to prove it actually shut.
You launched and nobody signed up: 10 reasons and the fix
Ten reasons nobody signed up, the move for each and how to tell it worked, plus twenty launch angles and where to find people already complaining.
It works locally but not on Vercel: 10 causes and fixes
Find your symptom, get the cause, the fix and the check that proves it. Plus a pre-flight for before you push and how to read a build log.
How to review AI code without reading it: 10 questions, 7 checks
Ten questions that make AI-written code confess, how to tell a real answer from a confident one, and seven hands-on checks. Two of them find data leaks.
Lovable, Cursor or Claude Code? The 12-question switch test
Twelve questions that tell you which kind of AI coding tool fits the task in front of you, the signs it is time to move, and what breaks when you do.
20 things to fix before a client touches your app
Twenty fixes that decide how a client demo goes, each with a copy-ready prompt and a way to prove it landed, plus the four no prompt can do for you.
AI cost control: 13 checks before you launch
Thirteen checks that stop a runaway AI bill, each with a copy-ready prompt and a way to prove it is actually working, plus a triage plan for after.
10 senior engineer prompts for safer AI coding
Ten copy-ready prompts that turn an AI coding session into reviewed, tested and recoverable engineering work.
The 5-file starter pack for AI coding
Five concise project files that give a coding agent stable product context, technical decisions, working rules and next steps.
The 5-prompt debug loop
Five copy-ready prompts that make a coding agent explain, narrow, test and prove a bug fix instead of guessing.
Blocking vs non blocking in Node, watch the thread pool
One readFileSync freezes every user on your server. Watch the thread stop on one line, then hand the read to a worker and answer everyone else meanwhile.
Temperature vs top-p, watch the sampling change
The model hands over odds; code after it draws a token. Watch temperature reshape those odds without reordering them, and top-p cut the tail out of the draw.
What is a context window, and why did it forget my name
A model has no memory between requests. Watch your app resend the whole chat every turn, fill the window, and drop the very turn that held your name.
401 vs 403, the difference in one request
401 means the server doesn't know who you are; 403 means it does, and the answer is no. Watch one request hit both gates.
Express middleware explained, step by step
Middleware is a line of functions every request walks before your handler. Watch three stations stamp one request in order, then a missing token stop it early.
How the Node event loop works, visually
Node runs on one thread yet never blocks. Watch one async callback wait in the queue and get pushed onto the call stack to see how.
HTTP status codes, the eight you need
You don't need dozens of status codes. Watch one request get 200, 301, 401, 404 and 500, learn the first digit rule, and keep the eight that cover real traffic.
JWT vs session authentication, which one to pick
Sessions can be revoked; JWTs verify themselves. Watch one request take each path, then pick the trade-off that fits what you are building.
What "port 3000 already in use" actually means
EADDRINUSE means a process is still listening on that port. Watch one machine give door 3000 to the first process, refuse the second, then fix it both ways.