What is the Skinory CS2 Index?
The Skinory CS2 Index tracks daily price changes with base 100 at each category’s first snapshot. It uses the weighted arithmetic mean of price ratios for matched items; weights are their previous-day price times listed quantity. Prices come from Skinport and Market.CSGO, using the reported median where available and otherwise the lowest listing. It is an analytical indicator, not a tradeable investment or a price forecast.
How a day is calculated
For each item present in both snapshots, divide today’s price by the previous snapshot price. Multiply each ratio by the item’s previous listed value, sum the results and divide by total matched weight. Multiply the previous index level by that weighted mean. This is not a median of ratios. The methodology gives the actual eligibility thresholds.
For example, equal previous listed values and price changes of +10% and −20% give a mean ratio of (1.10 + 0.80) / 2 = 0.95, a 5% decline. This two-item example illustrates the arithmetic; actual categories require more matched items. Ratios outside the permitted range are excluded rather than clipped. Stale snapshots are skipped, and newly appearing items do not enter that day’s matched comparison.
What it is for
The index answers the question "is the market up or down" with one dated number. Category sub-indexes, from knives and gloves to stickers, cases and charms, show which part of the market is moving. Weekly reports keep a permanent page per ISO week with the level, the change and the biggest movers, so a claim about the market can be cited with a date.
- The hub at /cs2-index shows the current level, 1, 7 and 30 day changes and every category.
- The market hub places the index next to the market cap, movers, arbitrage and deals.
GET /api/v1/indexandGET /api/v1/index/historyexpose index data as JSON. Skinory’s own derived indicators are available under CC BY 4.0; third-party raw prices and game assets retain their source rights. See the developers page.
Limits
The source basket prefers Skinport per market hash name, using Market.CSGO only when the Skinport price is unavailable. The selected source supplies the quantity and median price, falling back to its lowest listing; quantities are not summed across both sources for one name. It does not measure all completed CS2 trades. Listed quantities can change and affect future weights; source coverage is incomplete. Historical capitalization estimates before index launch are a separate series, not reconstructed index levels. Cite the category, snapshot date, data time and method alongside a value.
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Why does the index differ from the market cap?
Capitalization includes observed quantities and an assumed supply coefficient. The index compares matched price ratios, but quantities affect eligibility and subsequent weights. If all eligible matched prices remain unchanged, their weighted ratio is 1; a listing count alone is not a price change.
Can I cite the index in an article?
Yes. State Skinory, the snapshot date, category and comparison interval, and link to the index or relevant report. CC BY 4.0 applies to Skinory’s own derived indicators; it does not relicense third-party raw data.
Why is a category missing a level?
A category needs a minimum number of matched items between two days. Small categories may skip days until enough fresh listings exist on both sides.