If you receive RSUs or ESPP shares in one brokerage (Fidelity, Schwab, E*TRADE, Morgan Stanley) and trade in another (like Robinhood), there's a common tax-season trap: cross-account wash sales.
Under IRS rules, if you sell a stock at a loss and acquire substantially identical shares (including an RSU vest or ESPP purchase) within 30 days before or after that sale—even in a different account—that loss can be disallowed. Single-broker 1099-Bs don't see across accounts.
Instead of uploading sensitive brokerage CSVs to a cloud app or debugging local Python scripts, I built a free, zero-upload browser checker (WashSaleCheck: https://aiproject-4zm.pages.dev) using PapaParse and pure JavaScript.
Runs 100% in browser RAM (0 bytes sent to any server)
Auto-detects Fidelity, Schwab, E*TRADE, Morgan Stanley, and Robinhood CSV headers (plus manual column mapping)
Includes a 1-click "Load Sample Data" demo
(Diagnostic alert only — always verify flagged collisions with a CPA or tax software before filing Form 8949.)
