Choose a price benchmark before judging swap execution

Choose the benchmark according to the question. A price observed when you decided to trade measures the cost of carrying out that decision. A competing executable quote measures the opportunity available through another route. A price observed afterward measures something else: execution plus subsequent market movement.

Three answers from the same fill

Consider a hypothetical purchase of 10 tokens for 1,012 units of a stablecoin, excluding gas. At your decision time the reference price was 100 stablecoins per token. A comparable route quoted the same quantity at 1,008. By the time you review the receipt, the reference price has risen to 103.

• Against the decision-time benchmark, the purchase cost 12 more than 1,000.
• Against the alternative quote, it cost four more than 1,008, provided that alternative was actually available on comparable terms.
• Against the later valuation of 1,030, the tokens appear worth 18 more than the purchase cost. That does not establish superior execution.

A displayed spot price is not a large-trade offer

Uniswap's pricing guide separates the pool's mid price from a trade's average execution price. The first is a local reference; the second reflects a particular input and output quantity. Using the local price as though all tokens could trade there creates a benchmark gap even with correctly functioning execution.

That gap can still be useful. Name it as an execution shortfall relative to the reference, rather than assuming the entire difference was avoidable.

Make the comparison reproducible

Record the benchmark source, timestamp, direction, token identity, amount and fee treatment. For an alternative route, preserve its requested size and whether the quote was indicative or executable. Compare matching assets on matching networks. If the original benchmark was not recorded, say that the assessment is retrospective and approximate. A later chart price cannot reconstruct a missing contemporaneous offer.