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name: api-design description: Best practices for designing CosmWasm smart contract APIs. Use when defining message types, designing execute/query interfaces, or optimizing API ergonomics. license: BSD-3-Clause metadata: author: axone.xyz version: "1.0"

CosmWasm API Design Best Practices

This skill helps you design clean, minimal, and well-documented APIs for CosmWasm smart contracts.

When to use this skill

Use this skill when you need to:

• Define message types (InstantiateMsg, ExecuteMsg, QueryMsg, MigrateMsg)
• Design execute or query interfaces
• Document APIs for schema generation
• Apply serde patterns for optional fields
• Ensure API consistency across contracts

Core Principles

1. Minimalism - Include only what's necessary; avoid bloated APIs
2. Clarity - Names should be self-documenting
3. Consistency - Follow established patterns across all contracts
4. Documentation - Every public type and field must have doc comments

Message Type Patterns

InstantiateMsg

Copy/// Contract instantiation message
#[cosmwasm_schema::cw_serde]
#[derive(Default)]
pub struct MyContractInstantiateMsg {
    /// Optional configuration parameter with sensible default
    #[serde(default)]
    pub some_config: Option<String>,
}

Guidelines:

• Derive Default when possible for easier testing
• Use #[serde(default)] for optional fields
• Keep required fields minimal
• Document each field

ExecuteMsg

Copy/// Contract execute messages
#[cosmwasm_schema::cw_serde]
#[derive(cw_orch::ExecuteFns)]
pub enum MyContractExecuteMsg {
    /// Update the contract configuration
    UpdateConfig {
        /// New admin address (optional)
        new_admin: Option<String>,
    },
    /// Process an action with the given parameters
    ProcessAction {
        /// Unique identifier for the action
        action_id: String,
        /// Amount to process
        amount: Uint128,
    },
}

Guidelines:

• Use verb-based names (Update, Process, Create, Remove)
• Group related parameters in structs if >3 fields
• Document each variant AND each field
• Derive ExecuteFns for cw-orch integration

QueryMsg

Copy/// Contract query messages
#[cosmwasm_schema::cw_serde]
#[derive(cw_orch::QueryFns, QueryResponses)]
pub enum MyContractQueryMsg {
    /// Get the current configuration
    #[returns(ConfigResponse)]
    Config {},
    
    /// Get item by ID
    #[returns(ItemResponse)]
    Item {
        /// The item identifier
        id: String,
    },
    
    /// List all items with pagination
    #[returns(ItemsResponse)]
    Items {
        /// Start after this ID for pagination
        start_after: Option<String>,
        /// Maximum number of items to return
        limit: Option<u32>,
    },
}

Guidelines:

• Always include #[returns(ResponseType)] attribute
• Use noun-based names for queries
• Include pagination for list queries (start_after, limit)
• Derive QueryFns and QueryResponses

Response Types

Copy#[cosmwasm_schema::cw_serde]
pub struct ConfigResponse {
    /// Current admin address
    pub admin: Addr,
    /// Whether the contract is paused
    pub paused: bool,
}

#[cosmwasm_schema::cw_serde]
pub struct ItemsResponse {
    /// List of items
    pub items: Vec<ItemInfo>,
}

Guidelines:

• Response types should mirror what clients need
• Use specific types (Addr, Uint128) not strings
• Document all fields

Abstract SDK Integration

Use the app_msg_types! macro to generate wrapper types:

Copyuse crate::contract::MyContract;
use cosmwasm_schema::QueryResponses;

// Generates ExecuteMsg, QueryMsg, InstantiateMsg wrappers
abstract_app::app_msg_types!(MyContract, MyContractExecuteMsg, MyContractQueryMsg);

Documentation Standards

Rust Doc Comments

Copy/// Brief one-line description of the variant.
/// 
/// Optional longer description that explains:
/// - When to use this
/// - Side effects
/// - Related messages
/// 
/// # Errors
/// 
/// Returns `ContractError::Unauthorized` if caller is not admin.

Field Documentation

Every field must have a doc comment:

• Describe what the field represents
• Mention default values if applicable
• Note any constraints (min/max values, format)

Serde Patterns

Optional Fields with Defaults

Copy#[serde(default)]
pub optional_field: Option<String>,

#[serde(default = "default_limit")]
pub limit: u32,

fn default_limit() -> u32 {
    10
}

Flatten for Nested Configs

Copy#[cosmwasm_schema::cw_serde]
pub struct InstantiateMsg {
    #[serde(flatten)]
    pub base_config: BaseConfig,
    pub custom_field: String,
}

Rename for JSON Clarity

Copy#[serde(rename = "owner")]
pub owner_addr: Addr,

Checklist for New APIs

• All message variants have doc comments
• All struct fields have doc comments
• Query messages have #[returns(...)] attribute
• Execute messages describe potential errors
• Pagination is included for list queries
• Optional fields use Option<T> or #[serde(default)]
• Response types are defined for all queries
• Types use Addr/Uint128 not raw strings/numbers