As someone who invests in multiple exchange-traded funds, I realized there is no simple way to view an aggregated breakdown of all underlying holdings.
To the average person, this might seem inconsequential, but for anyone seeking a complete understanding of their portfolio exposures, it is a real problem. Having encountered this issue personally, and finding no great solutions available, I decided to build one myself.
The biggest challenge I encountered was that different ETF issuers use inconsistent formats for identifiers. Some use tickers (of varying formats) while others do not provide tickers at all—instead using identifiers like SIN, CUSIP, FIGI, or SEDOL. This inconsistency makes reliable aggregation and mapping of holdings significantly more complex.
I solved this by standardizing on the Yahoo Finance ticker format as the unified reference and creating larger master dictionaries to map all these identifiers to their corresponding tickers. This approach enabled consistent and reliable aggregation of holdings regardless of their initial format.
With coverage of over 1,400 ETFs, the system delivers broad market exposure and deep granularity. Known discrepancies affect less than 1% of total holdings—generally legacy assets, obscure securities, or minute residual positions that carry negligible dollar value.