What it is
A bookmarklet is a regular bookmark that, instead of opening a website, runs a small snippet of code. Ours reads the title and URL of the listing you’re viewing and opens The Back Catalog’s valuation for that item in a new tab. It loads no script onto the page and doesn’t modify the page you’re on.
Installing it
- Show your browser’s bookmarks bar. On most browsers that’s ⌘/Ctrl + Shift + B.
- Go to the bookmarklet page and drag the 💰 Value this page button up onto your bookmarks bar.
- If dragging isn’t possible (some browsers block it), use Or copy the bookmarklet code on that page, then create a new bookmark by hand and paste the code into its URL/address field.
Using it on a listing
- Open any product listing you’re curious about — say, a watch on eBay.
- Click the Value this page bookmark in your bookmarks bar.
- A new tab opens with that item’s resale price range, a breakdown by condition, and an authenticity signal for the platform it’s listed on.
Behind the scenes the bookmarklet hands the page’s title and link to the valuation tool, which matches it to a comparable item in our catalog. If the automatic match isn’t quite right, you can edit the item name there and re-run it.
Reading the result
- Price range — the low, high, and typical resale price drawn from real listings we track, broken down by condition where we have it.
- Authenticity signal — how trustworthy the selling platform’s provenance is, and whether authenticated copies tend to sell for a premium. This reflects the platform, not an inspection of the specific item, and is labelled as such.
- Confidence — how sure we are about the match. A low-confidence match is worth sanity-checking against the full product page.
Frequently asked questions
- Is the bookmarklet free?
- Yes. It's a free tool from The Back Catalog — there's nothing to buy and no account required.
- Is it an extension? Does it track me?
- No. A bookmarklet is just a bookmark that runs a tiny snippet when you click it. It loads no script onto the page, changes nothing on the listing, and runs only when you click it. It reads the page's title and URL purely to look up pricing.
- Which marketplaces does it support?
- It works on any product page. On marketplaces we track — eBay, Grailed, Depop, StockX, GOAT, The RealReal, Vestiaire Collective, Fashionphile, Chrono24, 1stDibs, Chairish and more — it can also show a platform authenticity signal.
- Why did it say it couldn't find the item?
- We match against the listings in our catalog. If an item is very new, very niche, or titled unusually, we may not have a comparable yet. Try the valuation tool and edit the item name, or search the catalog directly.
- Does it work on my phone?
- Bookmarklets are awkward on most mobile browsers. On a phone, the easiest path is to copy the listing's link and paste it into the valuation tool.
What data it reads
When you click the bookmarklet it sends only the listing’s title and URL to the valuation tool so we can look up a comparable. It doesn’t read your browsing history, your other tabs, or anything you haven’t clicked it on. See our privacy policy for how lookups are handled.