Reading a DEX trading pair without reversing the price

A token price is incomplete without units. “2” might mean two B per A or two A per B, which describe opposite values. In a swap, identify the token you sell and the token you receive before comparing any displayed rate.

Write the units next to the number

In a hypothetical market, one A is worth four B. The reference rates are 4 B per A and 0.25 A per B. These are reciprocals: multiplying them gives one. A screen that changes the base token can therefore change the number dramatically without changing the reference relationship.

A practical reading rule is to multiply your input amount by a rate whose denominator is the input token. Selling 10 A at 4 B per A suggests 40 B before considering whether that reference rate is executable for the full amount.

The reversed trade is a new quote

Taking the reciprocal of an average fill does not tell you what a separate reverse swap will receive. Pool state, trading fees and order size still matter. Uniswap's pricing documentation distinguishes calculations for input and output amounts based on reserves.

For example, if one completed trade spent 10 A and received 39 B, its average rate was 3.9 B per A. Writing that as approximately 0.25641 A per B is valid bookkeeping for that same trade. It is not a commitment to exchange those 39 B back for 10 A.

Pair names are conventions

Market interfaces use different display conventions for base and quote assets. A route can also list tokens in execution order while a chart labels them according to a fixed market convention. Read the amount labels rather than inferring direction from the pair's title.

For a comparison record, keep four fields together: sell token, sell amount, buy token and buy amount. Derive the displayed rate afterward. This avoids accidentally treating an inverted rate as a better offer or comparing a buy-side number with a sell-side number.