How does the collection book work?
The collection book turns every CS2 case into a page of slots. Each slot is one weapon skin from that case. Slots start grey and fill in with the skin's rarity color once you have pulled that skin in one of our simulators.
The book reads your simulated inventory from this browser. Pulls from the case simulator, case battles, the daily free case and the unbox challenges all count. It matches on the item name, so a StatTrak copy or a Battle-Scarred copy fills the same slot as any other copy.
Nothing here costs money. The items are simulated, have no value and cannot be traded.
What counts as completing a case?
A case page is complete when every weapon skin in it has been filled in. When that happens the page is marked with the date, you see a small celebration, and the case shows a green check in the list.
Knives and gloves are shown on each page as bonus slots. They do not count toward completing the page. Some cases share more than 60 knife and glove finishes, and each one is a 0.26% pull split many ways, so needing all of them would make a page close to impossible.
How long does it take to fill a page?
Most of the time goes into the rarest slots. Mil-Spec and Restricted skins show up fast. The Covert skins are what keep a page open, because each Covert pull is only 0.64% of all pulls and it has to land on the one skin you are missing.
We worked out these numbers from the published drop rates, assuming each skin inside a rarity tier is equally likely.
| Skins in the case (Mil-Spec / Restricted / Classified / Covert) | Average openings to complete | Half of tries done by | 9 in 10 done by |
|---|---|---|---|
| 7 / 5 / 3 / 2 (most modern cases) | 489 | 400 | 927 |
| 5 / 4 / 3 / 2 | 489 | 400 | 927 |
| 3 / 3 / 2 / 1 (small early cases) | 187 | 147 | 367 |
The first two rows are the same because the two Covert skins take so long that the extra blue and purple skins almost never matter. By the time you have both Coverts, you almost always have everything else.
Why does the last slot take so long?
This is the classic "collector's problem". Early on, almost every pull fills a new slot. Near the end, most pulls land on skins you already have.
Take the two Covert skins in a modern case. Your first Covert pull always fills a new slot. After that, only half of your Covert pulls are the one you still need. On average you need 3 Covert pulls to get both, and at 0.64% per opening that is about 469 openings. That one step is most of the 489 in the table.
What does a page look like after 100 openings?
Say you open 100 cases in the simulator from a case with 7 Mil-Spec, 5 Restricted, 3 Classified and 2 Covert skins.
- About 80 of those pulls are Mil-Spec, so all 7 Mil-Spec slots are almost sure to fill.
- About 16 are Restricted, which usually fills all 5 purple slots or leaves one open.
- About 3 are Classified, so you often have 2 of the 3 pink slots.
- The chance of even one Covert in 100 openings is about 47%.
So after 100 openings a typical page shows about 14 of 17 slots, often with the red row still grey.
How long does the last Covert take?
Now say you have 16 of 17 slots and only one Covert skin is missing. Each opening has a 0.64% chance of a Covert, and half of those are the one you need, so 0.32% per opening. That is about 1 in 313 on average, and 1 time in 10 it takes more than 700 more openings.
This is a good way to see why real case openers so often chase one last item and keep paying. The math does not care how close you are.
Where is my collection saved?
Everything is saved in your browser under this site. There is no account and nothing is sent to our server.
The simulator keeps only your newest 200 pulls in its inventory. The collection book keeps its own record, so every skin it has seen stays collected even after the simulator drops old pulls. Open the book now and then after big sessions so nothing slips past it.
A new browser, a private window or cleared site data starts a fresh book.
When should you use the collection book?
Use it to give your simulator sessions a goal. Pick a case, open it in the simulator and watch the page fill in. Check your level and best pulls on your profile card, and look at the drop rates page or the case odds calculator if you want the math behind a slot that will not fill.
For the real-world side of case contents, read how case drop pool changes affect prices.
