TransparentShort answer: instead of opening four tabs to judge whether a price is fair, the TransparentCars browser extension puts everything on the listing page itself: a fair-price range, the yearly road tax (IUC) for that exact car, and a red-flag checklist to run before you pay.
What the extension shows
It is a small browser extension. When you open a used-car listing, it reads the details already on the page — make, model, year, mileage, engine, price — and adds three useful things:
- A fair-price range: whether the asking price is fair, high or low, compared with similar listings. This is an estimate built from public market data, not an official tax-office figure and not a certified appraisal.
- The yearly IUC: the annual road tax you pay the state for owning that car. The extension works it out for that specific engine.
- A buyer's checklist: the red flags to look for before you pay, or even before you call the seller.
It works on StandVirtual, OLX and CustoJusto — the three places where most used cars in Portugal are listed. It is free and needs no account.
A real example: a 2014 Renault Clio
Say you open a 2014 Renault Clio with 120,000 km on StandVirtual. Without leaving the page, the extension shows:
- A fair-price band of about €7,600 to €9,870, with most similar listings near €8,750. If the seller asks €11,500, you can see at a glance it is above the market. If they ask €6,000, it is worth asking why.
- The yearly IUC for that engine, so you know the fixed cost before you decide.
- Two or three marks on the checklist. For example:
- mileage that does not match the year (too few kilometres for a car this old, or odd jumps against the history);
- no service record (missing maintenance book);
- a price that is too good to be true.
None of this replaces seeing the car in person. But it gives you an honest read in seconds, and saves you a morning spent comparing listings across several windows.
What you see on the listing
| What appears | The question it answers | Why it matters before you pay or call |
|---|---|---|
| Fair price | Is this price okay? | Shows whether the car is above or below the market, so you negotiate with a real number instead of a guess. |
| Yearly cost (IUC) | How much will I pay each year? | Two cars at the same price can carry very different road tax. Knowing it up front keeps your budget honest. |
| Red-flag checklist | What should I check? | Points out the usual risks (mileage, history, an odd price) before you spend time or money on a problem car. |
How to try it (status: coming soon)
Let's be honest about where it stands: the extension is coming soon to the Chrome Web Store — it is not published there yet, so there is no install link today. The source code is already public at github.com/transparentpt/chrome, for anyone who wants to see how it works under the hood.
While we finish the extension, you can get exactly the same numbers on the site: use the fair-price checker for the market range and the IUC calculator for the yearly tax. As soon as the extension is in the store, the link will appear on the extension page.
Privacy
The extension reads only the car details visible on the listing — make, model, year, mileage, engine and price. It does not collect your personal data and does not track you around the web. The details are on the extension page.
Related tools and reading
TransparentCars has other ways to get the same data. You can pull used cars into your ChatGPT, use the open car-price data over an API, or drop the price calculator onto your WordPress site.
Before you pay, also see how to read a used-car listing and spot the warning signs, and the checklist for inspecting a used car before you pay. And when you want it all in one place, start with the extension page.