How do you validate a startup idea?
You validate a startup idea by testing whether real people will pay for it, or at least act like they want it, before you build the whole thing. The cheapest validation happens before any code exists. The next step is a small MVP that lets real users try the core.
Here is a simple order to work through.
Start with conversations, not code
Talk to the people you think have the problem. Not friends being polite, actual potential customers. Ask what they do today and what it costs them. If the problem is not painful, no product will fix that.
Test demand cheaply
A landing page. Describe the product and ask people to sign up or join a waitlist. Drive a little traffic to it. Real sign-ups are a real signal.
A manual version. Deliver the service by hand before you automate it. If people pay for the manual version, the automated one has a market.
Pre-sales. The strongest signal of all is someone paying before the product exists.
Then build the smallest MVP
Once you have signals that people want it, build the smallest version that lets them actually use the core. Not the full vision. The one thing that proves it works. Put it in front of real users and watch what they do.
This is exactly what an MVP is for, and why keeping it small matters. You are still validating, just with working software now.
Do not skip straight to the big build
The expensive mistake is spending months building the full product before anyone has confirmed they want it. Validate first, build second, scale third.
When you are ready to build the MVP, tell me about your idea. You can also read how long an MVP takes.