---
name: using-cosmosdb-connector
description: Implements Azure CosmosDB container queries, CRUD, and patch operations using generated clients and MCP tools. Use when doing ANYTHING that touches CosmosDB or Cosmos DB in any way, load this skill.
---

# Major Platform Resource: Azure CosmosDB

## Common: Interacting with Resources

**Security**: Never connect directly to databases/APIs. Never use credentials in code. Always use generated clients or MCP tools.

**Two ways to interact with resources:**

1. **MCP tools** (direct, no code needed): Tools follow the pattern `mcp__resources__<resourcetype>_<toolname>`. Use `mcp__resources__list_resources` to discover available resources and their IDs.
2. **Generated TypeScript clients** (for app code): Call `mcp__resource-tools__add-resource-client` with a `resourceId` to generate a typed client. Clients are created in `/clients/` (Next.js) or `/src/clients/` (Vite).

**CRITICAL: Do NOT guess client method names or signatures.** The TypeScript clients in `@major-tech/resource-client` have strongly typed inputs and outputs. ALWAYS read the actual client source code in the generated `/clients/` directory (or the package itself) to verify available methods and their exact signatures before writing any client code.

**Framework note**: Next.js = resource clients must be used in server-side code only (Server Components, Server Actions, API Routes). Vite = call directly from frontend.

**Error handling**: Always check `result.ok` before accessing `result.result`.

**Invocation keys must be static strings** — use descriptive literals like `"fetch-user-orders"`, never dynamic values like `` `${date}-records` ``.

---

## MCP Tools

- `mcp__resources__cosmosdb_list_containers` — List containers with partition key info. Args: `resourceId`
- `mcp__resources__cosmosdb_describe_container` — Get partition key, indexing policy, unique keys. Args: `resourceId`, `container`
- `mcp__resources__cosmosdb_get_container_stats` — Get document count and storage size. Args: `resourceId`, `container`
- `mcp__resources__cosmosdb_query` — Execute a SQL query against a container. Args: `resourceId`, `container`, `query`, `parameters?`, `maxItemCount?`

## TypeScript Client

```typescript
import { cosmosClient } from "./clients";

// query<T>(container, query, invocationKey, options?)
const result = await cosmosClient.query<User>(
	"users",
	"SELECT * FROM c WHERE c.status = @status",
	"fetch-active-users",
	{
		parameters: [{ name: "@status", value: "active" }],
		partitionKey: "tenant-acme",
		maxItemCount: 50,
	},
);
if (result.ok) {
	console.log(result.result.documents);
	// Handle pagination: result.result.continuationToken
}

// Other methods: read, create, upsert, replace, delete, patch
await cosmosClient.patch<User>(
	"users",
	"user-456",
	"tenant-acme",
	[
		{ op: "set", path: "/name", value: "Jane" },
		{ op: "incr", path: "/loginCount", value: 1 },
	],
	"update-user",
);
```

## Tips

- **Partition key is required** for point operations (`read`, `replace`, `delete`, `patch`). Omit for cross-partition queries.
- Use `patch()` for partial updates — more efficient than full `replace()`
- Query parameters use `@param` syntax: `[{ name: "@status", value: "active" }]`
- Use `continuationToken` from query results for pagination through large result sets

**Docs**: [CosmosDB Documentation](https://learn.microsoft.com/en-us/azure/cosmos-db/)