Every word,
in plain language.

A link to a store that can earn us a small commission if you buy.

Some links on Vesim carry a tag that tells the store we sent you. If you buy, the store may pay us a commission. It never costs you more, it is disclosed wherever it appears, and it never changes the order results are shown in.

The number printed under the stripes on a box. Most things sold online don't have one.

Comparison sites usually match products by barcode. Unbranded goods sold by many resellers rarely carry one, and those are exactly the products where prices differ most. That is why Vesim matches the photo instead.

One source's whole list of products, read in one go.

A store or network publishes its products as a catalogue or feed. Vesim reads it, fingerprints every photo and merges the listings that show the same thing. One catalogue is connected today.

The lowest price for something, whether or not it fits what you asked.

It may ship from a country you excluded or break your budget in another way. Vesim shows it next to the cheapest that fits, and names the reason it doesn't qualify.

The lowest price among the sellers that meet everything you asked for.

If you say “a backpack under $25 that ships from the US”, the answer is the cheapest backpack that is under $25 and ships from the US. If nothing meets every requirement, Vesim says so rather than handing you a near miss.

What a store pays a site that sent it a sale.

Set by the store, paid only on some links, and kept away from the ranking: the code that adds an affiliate tag cannot see prices or positions.

Reading every price again each day. It has not started yet.

Price alerts, price history and the buy-now-or-wait verdicts all need it. History cannot be filled in backwards, so it begins on the first day the check runs.

A small add-on for your browser that checks the product page you are on.

It finds the main product photo on a shop's page, turns it into a fingerprint, and asks Vesim who else sells the same photo. Only those 64 bits leave your browser.

Two different products wrongly treated as the same one.

The mistake Vesim works hardest to avoid. Measured on 60 real product photos, the line Vesim uses made zero false matches across 1,762 pairs of different products.

A photo, shrunk to 64 bits that stay the same when the photo is resized or recompressed.

The photo is reduced to a tiny greyscale picture and turned into 64 ones and zeros that describe its shape of light and dark. Two copies of the same photo give the same, or nearly the same, fingerprint, even after a store resizes it.

How many of the 64 bits differ between two fingerprints.

Zero means the same photo. Unrelated photos differ in about 32 bits. Vesim treats two listings as the same product when their fingerprints are 10 bits apart or fewer.

Everything Vesim has read, fingerprinted and merged, ready to search.

Rebuilt from the connected catalogues. The date it was built, and every count in it, is on the status page.

One seller's page for a product.

The same product can have many listings, each with its own title and price. Vesim collapses them into one product so you can see every price at once.

Two listings Vesim has decided show the same product.

Decided by the photo, not the title. Both photos are always shown, so you can check the match yourself in half a second.

The set of product photos a supplier gives every reseller.

Resellers rarely photograph their own stock. They upload the supplier's photos unchanged, so the same picture appears on every listing of the same thing. That is what makes matching by photo work.

Two photos close to the line that Vesim keeps apart.

In the index there is a pair 14 bits apart with word-for-word the same title. Matching on titles would merge them; matching on photos does not.

One agreement that reaches thousands of stores at once.

Networks like FlexOffers and Rakuten gather stores that chose to be listed and compared. Connecting one network brings every store in it that approves us.

What Vesim says when it cannot check something, instead of guessing.

No connected source returns delivery dates, and network feeds don't say where things ship from. A requirement that can't be checked is shown as not measured, never quietly dropped.

One physical thing, however many places sell it.

Vesim's word for a product after its listings are merged: one object, every seller, every price.

The paid plan: unlimited alerts, price history and verdicts. A waitlist today.

$4.99 a month or $39 a year. It opens when the daily price check runs, and nobody is billed before then. The free plan stays free.

A message when something drops below the price you set.

Needs the daily price check, which has not started. Free will cover a few items; Plus has no limit.

How a product's price has moved over time.

It shows whether today's price is actually good. It begins the day the daily price check starts, and cannot be filled in backwards.

Of all the true matches, how many Vesim finds.

Measured at 98% on 60 real product photos. The 2% missed are photos changed so heavily (tiny thumbnails, heavy padding) that the safe choice is to miss them rather than guess.

Whoever you actually buy from.

Vesim sells nothing and holds no stock. Every link goes to the seller, who ships the product and handles returns.

The country a seller sends the parcel from.

The one delivery fact sellers declare. Say “ships from the US” and only listings that declare the US count. Some codes are routes, like China to the US, and are shown that way.

How much dearer the dearest seller is than the cheapest, for the same thing.

Written as a multiple: a spread of 1.5× means the dearest price is one and a half times the cheapest. Only shown when there are at least two sellers.

How different two photos may be and still count as the same product.

Set at 10 bits of 64. The closest two different products in the index sit 12 bits apart, so there is room between the line and the first mistake.

A list of people to tell when something opens.

Plus is a waitlist today. Joining costs nothing and you are never billed until Plus opens and you choose to start.