# Why every aggregator shows a different price for the same swap

> Canonical: https://blazephoenix.xyz/learn/why-aggregator-quotes-differ
> License: CC BY 4.0 (attribution + link) · © 2026 BlazePhoenix
> Updated: 2026-07-19

Five aggregators, five quotes: routing coverage, freshness, fee models and simulation honesty all differ — compare EXECUTED price, and prefer quotes you can reproduce with an eth_call.

Ask five aggregators to price the same swap and you get five numbers. Four honest reasons: they see different pool sets (routing coverage), at different moments (quote freshness vs the chain's state), with different fee models (some charge visibly, some by widening the quote, some sell your order flow), and they SIMULATE differently — an optimistic simulator quotes depth a pool advertises, a defensive one quotes only depth it can verify.

That last one is the trap: a quote that trusts advertised reserves can promise output a pool cannot deliver — the phantom-liquidity problem. The prettiest number on a comparison screen is sometimes the least executable one.

## How to compare quotes like an engineer

Compare EXECUTED price, not quoted price: quoted minus impact, minus fees, times fill probability. Ask three questions of any venue: where is the quote computed (a private server or the chain)? what happens to surplus when execution beats the quote (kept or returned)? and what enforces the minimum (a frontend or the contract)?

BlazePhoenix's answers are structural: the quote is computed by the on-chain Quoter — the same code that executes, so quote and execution cannot diverge by design; surplus is returned to the caller fee-exempt; and the floor is contract-derived (Iron Law Φ). Whichever venue you choose, make it show its work: a quote you cannot reproduce is a marketing number.

**Verify it yourself:** take any aggregator quote and replay it as an eth_call against the pools it claims to route through — ours reproduces because previewPlan IS the eth_call

Related: https://blazephoenix.xyz/learn/on-chain-quoting · https://blazephoenix.xyz/learn/what-is-a-dex-aggregator · https://blazephoenix.xyz/learn/phantom-liquidity