Methodology

In 2017, Chinese regulations required game publishers to disclose loot box probabilities. Valve complied by publishing the official drop rates for CS:GO weapon cases on the Chinese CS:GO website (csgo.com.cn). These rates represent the only official data Valve has ever released about case opening probabilities.

Case-sim.com uses these exact rates as the foundation for all weapon case simulations. The published rates cover the five standard rarity tiers — from Mil-Spec Grade (79.92%) down to Rare Special Items like knives and gloves (0.26%). These rates have remained consistent since their disclosure and are widely accepted by the community as the global standard, not just the Chinese client.

For souvenir packages, Valve published a separate six-tier distribution that we also implement exactly. Sticker, autograph, and patch capsule odds are based on extensive community research, as Valve has not published official rates for these container types.

Each simulated case opening follows the same probabilistic model as the real game. When you open a case, the simulator generates a random number and maps it to a rarity tier using Valve's published cumulative distribution. A second random roll determines the specific item within that tier, with each item in a given tier having an equal probability of being selected.

StatTrak variants are determined by an independent 10% roll on eligible items, matching the observed in-game rate. Float values (weapon wear) are generated within the item's defined float range using a uniform distribution, then mapped to the five wear categories: Factory New, Minimal Wear, Field-Tested, Well-Worn, and Battle-Scarred.

The random number generation uses the browser's built-in crypto.getRandomValues() API, which provides cryptographically secure randomness. This is the same class of RNG used by security-critical applications and produces results that are statistically indistinguishable from true randomness.

Item prices displayed in the simulator are sourced from the Steam Community Market. Prices are refreshed regularly to reflect current market conditions, including fluctuations from new case releases, major tournaments, and trade-up contract demand.

Each item's price is matched by its full market hash name — the unique identifier Steam uses internally — ensuring accurate price mapping even for items with similar display names. When a price is unavailable (for very new or very rare items with no recent sales), the simulator indicates this rather than displaying an estimated or fabricated price.

Price data powers the expected value calculations shown on individual case pages and the case odds breakdowns, helping users understand the real cost of case opening before spending money in-game.

Accuracy in a case simulator comes down to three things: correct probability distributions, complete item pools, and proper special-case handling. Case-sim.com addresses all three.

The probability distributions are taken directly from Valve's published data with no rounding or approximation. The item pools for each case are maintained to match the exact contents of in-game cases, including every skin, knife, and glove finish. When Valve adds new cases or updates existing ones, the simulator is updated to reflect those changes.

Special-case handling covers the details that many simulators get wrong: StatTrak eligibility varies by container type (weapon cases yes, souvenir packages no), float ranges differ per skin and affect wear category distribution, and Rare Special Items draw from a separate pool that includes all eligible knife or glove finishes for that case.

No simulator can perfectly replicate Valve's server-side implementation. While the published odds give us the rarity tier probabilities, the exact algorithm Valve uses for item selection within tiers, float value generation, and pattern seed assignment has never been disclosed. Our implementation uses uniform distributions where the true distribution is unknown.

Capsule odds (stickers, autographs, patches) are community-researched estimates rather than official Valve data. These are the best available approximations but may differ slightly from actual in-game rates.

Prices reflect Steam Community Market data and may not match third-party trading site valuations. Items with very low trade volume may show outdated prices.