Azure Storage Blob Ts Agent Skill

by microsoft

9k tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

2857

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/microsoft/skills --skill azure-storage-blob-ts

What comes with it

23 480 bytes besides the instruction

references/sas-tokens.md

references/streaming.md

The instruction itself

40 sections, as written by the author

@azure/storage-blob (TypeScript/JavaScript)

SDK for Azure Blob Storage operations — upload, download, list, and manage blobs and containers.

Installation

npm install @azure/storage-blob @azure/identity

Current Version: 12.x

Node.js: >= 18.0.0

Environment Variables

AZURE_STORAGE_ACCOUNT_NAME=<account-name>
AZURE_STORAGE_ACCOUNT_KEY=<account-key>
# OR connection string
AZURE_STORAGE_CONNECTION_STRING=DefaultEndpointsProtocol=https;AccountName=...
AZURE_TOKEN_CREDENTIALS=prod # Required only if DefaultAzureCredential is used in production

Authentication

Microsoft Entra Token Credential (Recommended)

import { BlobServiceClient } from "@azure/storage-blob";
import { DefaultAzureCredential, ManagedIdentityCredential } from "@azure/identity";

// Local dev: DefaultAzureCredential. Production: set AZURE_TOKEN_CREDENTIALS=prod or AZURE_TOKEN_CREDENTIALS=<specific_credential>
const credential = new DefaultAzureCredential({requiredEnvVars: ["AZURE_TOKEN_CREDENTIALS"]});
// Or use a specific credential directly in production:
// See https://learn.microsoft.com/javascript/api/overview/azure/identity-readme?view=azure-node-latest#credential-classes
// const credential = new ManagedIdentityCredential();

const accountName = process.env.AZURE_STORAGE_ACCOUNT_NAME!;
const client = new BlobServiceClient(
  `https://${accountName}.blob.core.windows.net`,
  credential
);

Connection String

import { BlobServiceClient } from "@azure/storage-blob";

const client = BlobServiceClient.fromConnectionString(
  process.env.AZURE_STORAGE_CONNECTION_STRING!
);

StorageSharedKeyCredential (Node.js only)

import { BlobServiceClient, StorageSharedKeyCredential } from "@azure/storage-blob";

const accountName = process.env.AZURE_STORAGE_ACCOUNT_NAME!;
const accountKey = process.env.AZURE_STORAGE_ACCOUNT_KEY!;

const sharedKeyCredential = new StorageSharedKeyCredential(accountName, accountKey);
const client = new BlobServiceClient(
  `https://${accountName}.blob.core.windows.net`,
  sharedKeyCredential
);

SAS Token

import { BlobServiceClient } from "@azure/storage-blob";

const accountName = process.env.AZURE_STORAGE_ACCOUNT_NAME!;
const sasToken = process.env.AZURE_STORAGE_SAS_TOKEN!; // starts with "?"

const client = new BlobServiceClient(
  `https://${accountName}.blob.core.windows.net${sasToken}`
);

Client Hierarchy

BlobServiceClient (account level)
└── ContainerClient (container level)
    └── BlobClient (blob level)
        ├── BlockBlobClient (block blobs - most common)
        ├── AppendBlobClient (append-only blobs)
        └── PageBlobClient (page blobs - VHDs)

Container Operations

Create Container

const containerClient = client.getContainerClient("my-container");
await containerClient.create();

// Or create if not exists
await containerClient.createIfNotExists();

List Containers

for await (const container of client.listContainers()) {
  console.log(container.name);
}

// With prefix filter
for await (const container of client.listContainers({ prefix: "logs-" })) {
  console.log(container.name);
}

Delete Container

await containerClient.delete();
// Or delete if exists
await containerClient.deleteIfExists();

Blob Operations

Upload Blob (Simple)

const containerClient = client.getContainerClient("my-container");
const blockBlobClient = containerClient.getBlockBlobClient("my-file.txt");

// Upload string
await blockBlobClient.upload("Hello, World!", 13);

// Upload Buffer
const buffer = Buffer.from("Hello, World!");
await blockBlobClient.upload(buffer, buffer.length);

Upload from File (Node.js only)

const blockBlobClient = containerClient.getBlockBlobClient("uploaded-file.txt");
await blockBlobClient.uploadFile("/path/to/local/file.txt");

Upload from Stream (Node.js only)

import * as fs from "fs";

const blockBlobClient = containerClient.getBlockBlobClient("streamed-file.txt");
const readStream = fs.createReadStream("/path/to/local/file.txt");

await blockBlobClient.uploadStream(readStream, 4 * 1024 * 1024, 5, {
  // bufferSize: 4MB, maxConcurrency: 5
  onProgress: (progress) => console.log(`Uploaded ${progress.loadedBytes} bytes`),
});

Upload from Browser

const blockBlobClient = containerClient.getBlockBlobClient("browser-upload.txt");

// From File input
const fileInput = document.getElementById("fileInput") as HTMLInputElement;
const file = fileInput.files![0];
await blockBlobClient.uploadData(file);

// From Blob/ArrayBuffer
const arrayBuffer = new ArrayBuffer(1024);
await blockBlobClient.uploadData(arrayBuffer);

Download Blob

const blobClient = containerClient.getBlobClient("my-file.txt");
const downloadResponse = await blobClient.download();

// Read as string (browser & Node.js)
const downloaded = await streamToText(downloadResponse.readableStreamBody!);

async function streamToText(readable: NodeJS.ReadableStream): Promise<string> {
  const chunks: Buffer[] = [];
  for await (const chunk of readable) {
    chunks.push(Buffer.from(chunk));
  }
  return Buffer.concat(chunks).toString("utf-8");
}

Download to File (Node.js only)

const blockBlobClient = containerClient.getBlockBlobClient("my-file.txt");
await blockBlobClient.downloadToFile("/path/to/local/destination.txt");

Download to Buffer (Node.js only)

const blockBlobClient = containerClient.getBlockBlobClient("my-file.txt");
const buffer = await blockBlobClient.downloadToBuffer();
console.log(buffer.toString());

List Blobs

// List all blobs
for await (const blob of containerClient.listBlobsFlat()) {
  console.log(blob.name, blob.properties.contentLength);
}

// List with prefix
for await (const blob of containerClient.listBlobsFlat({ prefix: "logs/" })) {
  console.log(blob.name);
}

// List by hierarchy (virtual directories)
for await (const item of containerClient.listBlobsByHierarchy("/")) {
  if (item.kind === "prefix") {
    console.log(`Directory: ${item.name}`);
  } else {
    console.log(`Blob: ${item.name}`);
  }
}

Delete Blob

const blobClient = containerClient.getBlobClient("my-file.txt");
await blobClient.delete();

// Delete if exists
await blobClient.deleteIfExists();

// Delete with snapshots
await blobClient.delete({ deleteSnapshots: "include" });

Copy Blob

const sourceBlobClient = containerClient.getBlobClient("source.txt");
const destBlobClient = containerClient.getBlobClient("destination.txt");

// Start copy operation
const copyPoller = await destBlobClient.beginCopyFromURL(sourceBlobClient.url);
await copyPoller.pollUntilDone();

Blob Properties & Metadata

Get Properties

const blobClient = containerClient.getBlobClient("my-file.txt");
const properties = await blobClient.getProperties();

console.log("Content-Type:", properties.contentType);
console.log("Content-Length:", properties.contentLength);
console.log("Last Modified:", properties.lastModified);
console.log("ETag:", properties.etag);

Set Metadata

await blobClient.setMetadata({
  author: "John Doe",
  category: "documents",
});

Set HTTP Headers

await blobClient.setHTTPHeaders({
  blobContentType: "text/plain",
  blobCacheControl: "max-age=3600",
  blobContentDisposition: "attachment; filename=download.txt",
});

SAS Token Generation (Node.js only)

Generate Blob SAS

import {
  BlobSASPermissions,
  generateBlobSASQueryParameters,
  StorageSharedKeyCredential,
} from "@azure/storage-blob";

const sharedKeyCredential = new StorageSharedKeyCredential(accountName, accountKey);

const sasToken = generateBlobSASQueryParameters(
  {
    containerName: "my-container",
    blobName: "my-file.txt",
    permissions: BlobSASPermissions.parse("r"), // read only
    startsOn: new Date(),
    expiresOn: new Date(Date.now() + 3600 * 1000), // 1 hour
  },
  sharedKeyCredential
).toString();

const sasUrl = `https://${accountName}.blob.core.windows.net/my-container/my-file.txt?${sasToken}`;

Generate Container SAS

import { ContainerSASPermissions, generateBlobSASQueryParameters } from "@azure/storage-blob";

const sasToken = generateBlobSASQueryParameters(
  {
    containerName: "my-container",
    permissions: ContainerSASPermissions.parse("racwdl"), // read, add, create, write, delete, list
    expiresOn: new Date(Date.now() + 24 * 3600 * 1000), // 24 hours
  },
  sharedKeyCredential
).toString();

Generate Account SAS

import {
  AccountSASPermissions,
  AccountSASResourceTypes,
  AccountSASServices,
  generateAccountSASQueryParameters,
} from "@azure/storage-blob";

const sasToken = generateAccountSASQueryParameters(
  {
    services: AccountSASServices.parse("b").toString(), // blob
    resourceTypes: AccountSASResourceTypes.parse("sco").toString(), // service, container, object
    permissions: AccountSASPermissions.parse("rwdlacupi"), // all permissions
    expiresOn: new Date(Date.now() + 24 * 3600 * 1000),
  },
  sharedKeyCredential
).toString();

Blob Types

Block Blob (Default)

Most common type for text and binary files.

const blockBlobClient = containerClient.getBlockBlobClient("document.pdf");
await blockBlobClient.uploadFile("/path/to/document.pdf");

Append Blob

Optimized for append operations (logs, audit trails).

const appendBlobClient = containerClient.getAppendBlobClient("app.log");

// Create the append blob
await appendBlobClient.create();

// Append data
await appendBlobClient.appendBlock("Log entry 1\n", 12);
await appendBlobClient.appendBlock("Log entry 2\n", 12);

Page Blob

Fixed-size blobs for random read/write (VHDs).

const pageBlobClient = containerClient.getPageBlobClient("disk.vhd");

// Create 512-byte aligned page blob
await pageBlobClient.create(1024 * 1024); // 1MB

// Write pages (must be 512-byte aligned)
const buffer = Buffer.alloc(512);
await pageBlobClient.uploadPages(buffer, 0, 512);

Error Handling

import { RestError } from "@azure/storage-blob";

try {
  await containerClient.create();
} catch (error) {
  if (error instanceof RestError) {
    switch (error.statusCode) {
      case 404:
        console.log("Container not found");
        break;
      case 409:
        console.log("Container already exists");
        break;
      case 403:
        console.log("Access denied");
        break;
      default:
        console.error(`Storage error ${error.statusCode}: ${error.message}`);
    }
  }
  throw error;
}

TypeScript Types Reference

import {
  // Clients
  BlobServiceClient,
  ContainerClient,
  BlobClient,
  BlockBlobClient,
  AppendBlobClient,
  PageBlobClient,

  // Authentication
  StorageSharedKeyCredential,
  AnonymousCredential,

  // SAS
  BlobSASPermissions,
  ContainerSASPermissions,
  AccountSASPermissions,
  AccountSASServices,
  AccountSASResourceTypes,
  generateBlobSASQueryParameters,
  generateAccountSASQueryParameters,

  // Options & Responses
  BlobDownloadResponseParsed,
  BlobUploadCommonResponse,
  ContainerCreateResponse,
  BlobItem,
  ContainerItem,

  // Errors
  RestError,
} from "@azure/storage-blob";

Best Practices

Use DefaultAzureCredential for local development; use ManagedIdentityCredential or WorkloadIdentityCredential for production
Use streaming for large files — uploadStream/downloadToFile for files > 256MB
Set appropriate content types — Use setHTTPHeaders for correct MIME types
Use SAS tokens for client access — Generate short-lived tokens for browser uploads
Handle errors gracefully — Check RestError.statusCode for specific handling
Use *IfNotExists methods — For idempotent container/blob creation
Close clients — Not required but good practice in long-running apps

Platform Differences

| Feature | Node.js | Browser |

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

| StorageSharedKeyCredential | ✅ | ❌ |

| uploadFile() | ✅ | ❌ |

| uploadStream() | ✅ | ❌ |

| downloadToFile() | ✅ | ❌ |

| downloadToBuffer() | ✅ | ❌ |

| uploadData() | ✅ | ✅ |

| SAS generation | ✅ | ❌ |

| DefaultAzureCredential | ✅ | ❌ |

| Anonymous/SAS access | ✅ | ✅ |

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How to use it

Copy the folder

Take microsoft/azure-storage-blob-ts from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

The agent identifies a skill by the name field in its header. Two skills with the same name cannot sit side by side — one of them will be ignored.

Install what it needs

The instructions reference npm. Without those the skill loads but fails at the first command.