MultiversX Cross-Contract Storage Reads Skill

MultiversX Cross-Contract Storage Reads

Read another contract's storage mappers directly — zero gas overhead from proxy calls, no async complexity.

When to Use

| Criteria | storage_mapper_from_address | Proxy Call | |---|---|---| | Same shard only | Yes (required) | Works cross-shard | | Read-only | Yes | Read + Write | | Needs computation on target | No | Yes | | Gas cost | ~storage read cost | ~execution + storage | | Requires knowing storage keys | Yes | No (uses ABI) |

Core Pattern

#[multiversx_sc::module]
pub trait ExternalStorageModule {
    // Simple value
    #[storage_mapper_from_address("total_supply")]
    fn external_total_supply(&self, contract_address: ManagedAddress) -> SingleValueMapper<BigUint, ManagedAddress>;

    // Composite key (token-specific)
    #[storage_mapper_from_address("balance")]
    fn external_balance(&self, contract_address: ManagedAddress, token_id: &TokenIdentifier) -> SingleValueMapper<BigUint, ManagedAddress>;

    // Module-prefixed key
    #[storage_mapper_from_address("pause_module:paused")]
    fn external_paused(&self, contract_address: ManagedAddress) -> SingleValueMapper<bool, ManagedAddress>;
}

Key Rules

String must EXACTLY match storage key in target contract
First param must be ManagedAddress
Return type's second generic must be ManagedAddress
Additional params become composite key parts

How to Discover Storage Keys

Source code: #[storage_mapper("key")] in target
ABI: .abi.json lists all keys
Module keys: prefixed like pause_module:paused

Security

Same-shard only: Cross-shard reads return defaults silently — no error
Stale data: Reflects target's state as of current block
Key changes: If target renames keys in upgrade, reads break silently
Read-only: Cannot write to another contract's storage

Anti-Patterns

Not validating empty results (get default 0/false silently)
Not validating target is on same shard

Agent Skills: MultiversX Cross-Contract Storage Reads

Install this agent skill to your local