# Query Functions

# Overview

Queries provide the ability to simulate an operation and find its result without executing a transaction. Balancer Routers provide a query for all state changing liquidity operations. An example of how this is useful can be seen when setting slippage limits.

# Router queries

The detailed Router API description can be found in the Router API section.

• queryAddLiquidityUnbalanced
• queryAddLiquiditySingleTokenExactOut
• queryAddLiquidityCustom
• queryRemoveLiquidityProportional
• queryRemoveLiquiditySingleTokenExactIn
• queryRemoveLiquiditySingleTokenExactOut
• queryRemoveLiquidityCustom
• queryRemoveLiquidityCustom
• queryRemoveLiquidityRecovery
• querySwapSingleTokenExactIn
• querySwapSingleTokenExactOut
• querySwapExactIn
• querySwapExactOut

# Batch Router queries

The detailed Router API description can be found in the Batch Router API section.

• querySwapExactIn
• querySwapExactOut

# Complex queries

The Router and Batch Router are primarily used as entrypoints for standard queries. However, Balancer's design allows for a more flexible querying mechanism. Any Vault operation that includes a onlyWhenUnlocked modifier can be queried natively.

# Quote

This is facilitated through a quote mechanism. The concept of Transient Accounting enables the querying of complex Vault operations. To execute a query, the Router invokes the quote function on the Vault.

The Vault requires that any invocation of quote be executed as a staticcall (ensured by the query modifier). Within the quote context, the Router has the flexibility to carry out a series of complex actions without the need to settle any debt.

# quoteAndRevert

Since quote changes the Vault state some query combinations are not possible. For example, if you wanted to quote querySwapExactIn for POOL_A but also querySwapExactOut for POOL_A in its initial state, you would have to use quoteAndRevert. In this variant, the call always reverts and returns the result in the revert data (similar to the v2 mechanism).