Azure Cosmos Rust Agent Skill

Azure Cosmos DB library for Rust

Client library for Azure Cosmos DB NoSQL API — document CRUD, containers, and globally distributed data.

Use this skill when:

• An app needs to store or query documents in Cosmos DB from Rust
• You need CRUD operations on items with partition keys
• You need key-based auth as an alternative to Entra ID

> IMPORTANT: Only use the official azure_data_cosmos crate published by the azure-sdk crates.io user. Do NOT use the unofficial azure_cosmos or azure_sdk_for_rust community crates. Official crates use underscores in names and none have version 0.21.0.

Installation

cargo add azure_data_cosmos azure_identity serde serde_json tokio

> If your code uses azure_core types directly (for example, azure_core::credentials::TokenCredential), add azure_core to Cargo.toml. If you only use azure_data_cosmos re-exports, direct azure_core dependency is optional.

Environment Variables

COSMOS_ENDPOINT=https://<account>.documents.azure.com/ # Required for all operations

Authentication

Rust Azure SDK code must not use DefaultAzureCredential. The Rust identity crate does not provide that type.

use azure_identity::DeveloperToolsCredential;
use azure_data_cosmos::{
    CosmosClient, AccountReference, AccountEndpoint, RoutingStrategy,
};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Local dev: DeveloperToolsCredential. Production: use ManagedIdentityCredential.
    let credential = DeveloperToolsCredential::new(None)?;
    let endpoint: AccountEndpoint = "https://<account>.documents.azure.com/"
        .parse()?;
    let account = AccountReference::with_credential(endpoint, credential);
    let client = CosmosClient::builder()
        .build(account, RoutingStrategy::ProximityTo("East US".into()))
        .await?;
    Ok(())
}

Prefer the crate README/examples when checking builder signatures and CRUD method shapes instead of reconstructing APIs from memory or generated internals.

Client Hierarchy

| Client | Purpose | Access |

| ----------------- | ------------------------- | ----------------------------------------------- |

| CosmosClient | Account-level operations | CosmosClient::builder().build(account).await? |

| DatabaseClient | Database operations | client.database_client("db") |

| ContainerClient | Container/item operations | database.container_client("c").await |

Core Workflow

use serde::{Serialize, Deserialize};
use azure_data_cosmos::CosmosClient;

#[derive(Serialize, Deserialize)]
struct Item {
    pub id: String,
    pub partition_key: String,
    pub value: String,
}

async fn crud(client: CosmosClient) -> Result<(), Box<dyn std::error::Error>> {
    let container = client
        .database_client("myDatabase")
        .container_client("myContainer")
        .await;

    let item = Item {
        id: "1".into(),
        partition_key: "pk1".into(),
        value: "hello".into(),
    };

    // Create
    container.create_item("pk1", "1", item, None).await?;

    // Read
    let resp = container.read_item("pk1", "1", None).await?;
    let mut item: Item = resp.into_model()?;

    // Update
    item.value = "updated".into();
    container.replace_item("pk1", "1", item, None).await?;

    // Delete
    container.delete_item("pk1", "1", None).await?;
    Ok(())
}

Patch Item

use azure_data_cosmos::{PatchInstructions, PatchOperation};

let patch = PatchInstructions::from(vec![
    PatchOperation::set("/value", serde_json::json!("patched")),
]);
let patched: Item = container
    .patch_item("pk1", "1", patch, None)
    .await?
    .into_model()?;
println!("Patched value: {}", patched.value);

Key Auth (Optional)

Enable account key authentication with the feature flag:

cargo add azure_data_cosmos --features key_auth

RBAC Roles

For Entra ID auth, assign one of these built-in Cosmos DB roles:

| Role | Access |

| ------------------------------------- | ---------- |

| Cosmos DB Built-in Data Reader | Read-only |

| Cosmos DB Built-in Data Contributor | Read/write |

Best Practices

• Use cargo add to manage dependencies, never edit Cargo.toml directly. Add and remove Rust SDK dependencies with cargo commands instead of manual manifest edits.
• Add azure_core only when importing azure_core types directly. If your code imports azure_core::http::Url, azure_core::http::RequestContent, or azure_core::error::ErrorKind, include azure_core; otherwise a direct dependency is optional.
• Use DeveloperToolsCredential for local dev, ManagedIdentityCredential for production — Rust does not provide a single DefaultAzureCredential type
• Never hardcode credentials — use environment variables or managed identity
• Reuse CosmosClient — clients are thread-safe; create once, share across tasks
• Use RoutingStrategy::ProximityTo — route to the nearest region for lowest latency
• Always specify partition key for item operations — Cosmos DB requires it for all CRUD
• Run cargo clippy -- -D warnings when the prompt, eval, or CI expects lint-clean output
• Future-proof #[non_exhaustive] SDK models — when constructing SDK model/options structs, end the initializer with ..Default::default() (add #[allow(clippy::needless_update)]) and use a _ wildcard arm when matching SDK enums, so new service-added fields/variants don't break your build

Reference Links

| Resource | Link |

| ------------- | ---------------------------------------------------------------------------------- |

| API Reference | https://docs.rs/azure_data_cosmos/latest/azure_data_cosmos |

| crates.io | https://crates.io/crates/azure_data_cosmos |

| Source Code | https://github.com/Azure/azure-sdk-for-rust/tree/main/sdk/cosmos/azure_data_cosmos |