# Swap routing and aggregators: selecting a path through liquidity

A swap router executes a path through one or more pools. An aggregator compares available paths or liquidity sources and may split a trade. The most useful comparison includes fees and execution costs; a route with the largest gross token output can still have a lower net result.

Evidence: [Introducing the Auto Router](https://blog.uniswap.org/auto-router); [Uniswap v2 pricing](https://developers.uniswap.org/docs/protocols/v2/concepts/pricing)

Canonical: https://degreesofsatoshi.com/encyclopedia/swap-routing-and-aggregators/
Published: 2026-10-02
Substantively modified: 2026-10-02
Independently verified by an automated reviewer: 2026-10-02T15:08:18.373Z

AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied.

## Key facts

- **Multiple hops:** A route can exchange A for an intermediate token before B. ([Introducing the Auto Router](https://blog.uniswap.org/auto-router))
- **Split execution:** Routing can divide an input across several pools. ([Introducing the Auto Router](https://blog.uniswap.org/auto-router))
- **Permission:** The spender authorized for routing is a specific contract. ([ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20))

## Think of pools as possible paths

A direct A-to-B pool is one path. An A-to-C pool followed by C-to-B is another. Splitting the input can also reduce how far any one pool moves along its curve, at the cost of more contract work.

Uniswap’s September 2021 Auto Router announcement is a dated example: it describes split routing and considering gas when choosing a path. It does not establish which routes, venues or cost estimates any current aggregator uses.

Evidence: [Introducing the Auto Router](https://blog.uniswap.org/auto-router)

## Compare like-for-like output

Imagine route one delivers 1,000 quote-token units with an execution cost valued at 2 of those units. Route two delivers 1,003 but costs 7. The illustrative net amounts are 998 and 996 respectively, before any extra interface charges or uncertainty.

This comparison depends on valuing the gas asset in the same unit and at the same time. A longer path can win for a large swap and lose for a small one. An off-chain route search is an estimate until the encoded transaction executes.

Evidence: [Introducing the Auto Router](https://blog.uniswap.org/auto-router)

## Inspect the transaction behind the quote

The route, permitted spender, recipient, input and final minimum output are concrete parts of the request. An attractive displayed price does not justify an unrelated approval or a different recipient.

An aggregator searches its supported venues and assumptions; it cannot prove that no better executable trade exists anywhere. Quotes may expire as state changes, and a route can fail if any required operation or final bound fails.

Evidence: [Uniswap v2 pricing](https://developers.uniswap.org/docs/protocols/v2/concepts/pricing); [ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20)

## Questions

### Does an aggregator always choose the best trade?

It can compare the venues and routes it supports using its own cost estimates. That is not a guarantee of the best executable result across all markets or future states.

Evidence: [Introducing the Auto Router](https://blog.uniswap.org/auto-router); [Uniswap v2 pricing](https://developers.uniswap.org/docs/protocols/v2/concepts/pricing)

## Claims and scope

### swap-routing-and-aggregators-quick-answer

A swap router executes a path through one or more pools. An aggregator compares available paths or liquidity sources and may split a trade. The most useful comparison includes fees and execution costs; a route with the largest gross token output can still have a lower net result.

Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null}

### swap-routing-and-aggregators-fact-multiple-hops

Multiple hops: A route can exchange A for an intermediate token before B.

Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null}

### swap-routing-and-aggregators-fact-split-execution

Split execution: Routing can divide an input across several pools.

Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null}

### swap-routing-and-aggregators-fact-permission

Permission: The spender authorized for routing is a specific contract.

Scope: {"collection":"defi","dataAsOf":null,"blockHeight":null}

## Sources

- [Introducing the Auto Router](https://blog.uniswap.org/auto-router) — Uniswap Labs. A dated implementation example of routing across pools with gas-aware optimization. Locator: Split Routes; Gas Cost Awareness. Retrieved: 2026-10-02.
- [Uniswap v2 pricing](https://developers.uniswap.org/docs/protocols/v2/concepts/pricing) — Uniswap. Reserve-dependent quotes, trade bounds and external price observations. Locator: Pricing Trades; Exact Input; Exact Output. Retrieved: 2026-10-02.
- [ERC-20: Token Standard](https://eips.ethereum.org/EIPS/eip-20) — Ethereum Improvement Proposals. The token spending allowance is separate from a website connection. Locator: Methods: approve, allowance, transferFrom. Retrieved: 2026-10-02.

## Revision history

- 2026-10-02: First publication after primary-source research and independent automated verification.

## Cite this entry

Degrees of Satoshi editorial project. “Swap routing and aggregators: selecting a path through liquidity.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/swap-routing-and-aggregators/