I used to think that tax reporting was just exporting the exchange transaction history at the end of the year... but it turns out there's a bunch of routing changes, split transactions, slippage compensation on the chain, and the exported data doesn't look like something a person can easily read.

Now my understanding is: don't wait until the end of the year, clarify what each transaction is doing on the day it happens, or you'll be out of sync with yourself later.

My current method is pretty rough: for every large swap/cross-chain/airdrop, I save the transaction hash + a screenshot (showing the traded currency, amount, and purpose at the time), then group wallet addresses by purpose; for routes that are too complex, I also save the aggregator's path page.
Basically, it's leaving evidence for my future self.

Recently, people have been criticizing validators for MEV extraction and unfair ordering, and my real feeling is: when you're sandwich attacked, not only do you lose on the books, but you also end up with a bunch of "unintelligible transactions," making tax reporting even more stressful...
Anyway, I now prefer to spend an extra two minutes organizing everything, rather than cursing at the browser during year-end.