What the router searches
Direct pools for your pair, and multi-hop paths through intermediate tokens where that produces a better result. It simulates each candidate against live account state and compares the output after fees.
Because Solana transaction fees are low and compute is the binding constraint, more complex routes are economically viable than on an expensive EVM chain.
Splitting and atomicity
A large order can be divided across several venues so that each portion sits in the shallow part of its curve. All of it executes in one transaction, so either the whole route completes or none of it does.
Atomicity matters: there is no state where half the swap happened and you are holding an unintended intermediate token.
Compute limits as the real constraint
Each transaction has a compute budget. A route with many hops and venues can exceed it, which causes the transaction to fail. This is why very complex routes sometimes revert while simpler ones succeed.
Clients mitigate by setting an explicit compute limit and by preferring routes that fit comfortably within it.
Account contention is the other constraint. Two transactions writing to the same pool cannot execute in parallel, so a route through a heavily used pool competes for that account. This is why popular routes degrade during activity spikes while obscure ones keep working.
What you should still check
The quote, the price impact and the slippage tolerance, exactly as on any chain. For a Token-2022 mint, check whether a transfer fee applies, because it affects the amount that actually arrives.
FBT Swap routes Solana swaps through public aggregators and shows the route, price impact and fee before your wallet signs.