Trusted benchmarks for the TCG market.

The stock market has the S&P 500. Forex has USD/JPY. But trading cards?

Today, to understand card prices you have to search individual external marketplaces or check specific shop buy prices. That's “point” data — there's no “line” showing the overall market trend.

The result: no one can objectively say whether the market is rising or falling. That's the fundamental opacity of the TCG market.

GCI calculates indices through a 4-stage pipeline.

1. 1

   Collection

   We collect transaction data from multiple secondary markets, referencing both active listings and sold listings, prioritizing actual completed transactions.

2. 2

   Filtering

   PSA-graded cards, lot sales, counterfeits, and unknown-condition listings are automatically excluded. Remaining data is cleaned with IQR outlier detection to remove anomalies that distort the market.

3. 3

   Index Calculation

   A TrustScore-weighted average (source reliability, listing type, condition) is calculated on the clean data, expressed as an index with base value 1000.

4. 4

   Confidence Scoring

   HIGH / MED / LOW confidence is derived from sample count and outlier ratio, published alongside the index value. Indices with insufficient data are hidden and marked as reference values.