Blaxel SDK

Blaxel Skill Reference

What is Blaxel

Blaxel (https://blaxel.ai) is a cloud platform that gives AI agents their own compute environments. Its flagship product is perpetual sandboxes: instant-launching microVMs that resume from standby in under 25ms and scale to zero after a few seconds of inactivity.

You use Blaxel primarily to:

• Spin up a sandbox, install dependencies, run a dev server, and expose a live preview URL
• Build and deploy sandbox templates (custom Docker images) for reusable environments
• Deploy AI agents, MCP servers, and batch jobs as serverless endpoints

SDKs: TypeScript (@blaxel/core) and Python (blaxel) CLI: bl (install from https://docs.blaxel.ai/cli-reference/introduction) Docs: https://docs.blaxel.ai

Authentication

The SDK authenticates using these sources in priority order:

1. Blaxel CLI, when logged in
2. Environment variables in .env file (BL_WORKSPACE, BL_API_KEY)
3. System environment variables
4. Blaxel configuration file (~/.blaxel/config.yaml)

Log in locally (recommended for development):

bl login YOUR-WORKSPACE

Or set environment variables (for remote/CI environments):

export BL_WORKSPACE=your-workspace
export BL_API_KEY=your-api-key

When running on Blaxel itself, authentication is automatic.

Sandbox workflow (primary use case)

This is the most common workflow: create a sandbox, run commands in it, and get a preview URL.

Step 1: Create a sandbox

Use a public image from the Blaxel Hub (https://github.com/blaxel-ai/sandbox/tree/main/hub):

• blaxel/base-image:latest — minimal Linux
• blaxel/node:latest — Node.js
• blaxel/nextjs:latest — Next.js
• blaxel/vite:latest — Vite
• blaxel/expo:latest — Expo (React Native)
• blaxel/py-app:latest — Python

Or use a custom template image you deployed yourself.

Declare the ports you need at creation time. Ports cannot be added after creation. Ports 80, 443, and 8080 are reserved.

import { SandboxInstance } from "@blaxel/core";

const sandbox = await SandboxInstance.createIfNotExists({
  name: "my-sandbox",
  image: "blaxel/base-image:latest",
  memory: 4096,
  ports: [{ target: 3000, protocol: "HTTP" }],
});

from blaxel.core import SandboxInstance

sandbox = await SandboxInstance.create_if_not_exists({
  "name": "my-sandbox",
  "image": "blaxel/base-image:latest",
  "memory": 4096,
  "ports": [{"target": 3000, "protocol": "HTTP"}],
})

Use createIfNotExists / create_if_not_exists to reuse an existing sandbox by name or create a new one.

Always prefer this over a get-then-create fallback. Deleted sandboxes are kept in TERMINATED state for a few minutes (so their logs stay accessible), which means a plain get can return a dead sandbox whose gateway and preview URLs fail with workload-not-found. createIfNotExists checks the status for you and recreates the sandbox when the existing record is FAILED, TERMINATED, TERMINATING, or DELETING. As of @blaxel/core 0.2.88 / blaxel 0.2.55, it also waits out the brief DELETING window right after a delete, so delete-then-recreate works directly. On older SDK versions that window can throw "Unable to create sandbox after 3 attempts" — wait a moment and retry, or upgrade. If you must use get, check sandbox.status before reusing the instance.

Step 2: Write files and run commands

// Write files
await sandbox.fs.write("/app/package.json", JSON.stringify({
  name: "my-app",
  scripts: { dev: "astro dev --host 0.0.0.0 --port 3000" },
  dependencies: { "astro": "latest" }
}));

// Or write multiple files at once
await sandbox.fs.writeTree([
  { path: "src/pages/index.astro", content: "<h1>Hello</h1>" },
  { path: "astro.config.mjs", content: "import { defineConfig } from 'astro/config';\nexport default defineConfig({});" },
], "/app");

// Execute a command and wait for it to finish
const install = await sandbox.process.exec({
  name: "install",
  command: "npm install",
  workingDir: "/app",
  waitForCompletion: true,
  timeout: 60, // seconds (default 600; 0 = no auto-kill with keepAlive)
});

// Start a long-running dev server (don't wait for completion)
const devServer = await sandbox.process.exec({
  name: "dev-server",
  command: "npm run dev",
  workingDir: "/app",
  waitForPorts: [3000],  // returns once port 3000 is open
});

await sandbox.fs.write("/app/package.json", '{"name":"my-app","scripts":{"dev":"astro dev --host 0.0.0.0 --port 3000"},"dependencies":{"astro":"latest"}}')

await sandbox.fs.write_tree([
  {"path": "src/pages/index.astro", "content": "<h1>Hello</h1>"},
  {"path": "astro.config.mjs", "content": "import { defineConfig } from 'astro/config';\nexport default defineConfig({});"},
], "/app")

install = await sandbox.process.exec({
  "name": "install",
  "command": "npm install",
  "working_dir": "/app",
  "wait_for_completion": True,
  "timeout": 60,  # seconds (default 600; 0 = no auto-kill with keep_alive)
})

dev_server = await sandbox.process.exec({
  "name": "dev-server",
  "command": "npm run dev",
  "working_dir": "/app",
  "wait_for_ports": [3000],
})

IMPORTANT: Dev servers must bind to 0.0.0.0 (not localhost) to be reachable through preview URLs. Use --host 0.0.0.0 or the HOST env variable.

Step 3: Create a preview URL

const preview = await sandbox.previews.createIfNotExists({
  metadata: { name: "app-preview" },
  spec: { port: 3000, public: true },
});
const url = preview.spec?.url;
// url => https://xxxx.us-pdx-1.preview.bl.run

preview = await sandbox.previews.create_if_not_exists({
  "metadata": {"name": "app-preview"},
  "spec": {"port": 3000, "public": True},
})
url = preview.spec.url

For private previews, set public: false and create a token:

const preview = await sandbox.previews.createIfNotExists({
  metadata: { name: "private-preview" },
  spec: { port: 3000, public: false },
});
const token = await preview.tokens.create(new Date(Date.now() + 10 * 60 * 1000));
// Access: preview.spec?.url + "?bl_preview_token=" + token.value

Step 4: Manage the sandbox

// Reconnect to an existing sandbox. Careful: get can return a recently
// deleted sandbox still in TERMINATED state — check status before reuse,
// or use createIfNotExists which handles this for you.
const sandbox = await SandboxInstance.get("my-sandbox");

// List files
const { subdirectories, files } = await sandbox.fs.ls("/app");

// Read a file
const content = await sandbox.fs.read("/app/src/pages/index.astro");

// Get process info / logs
const proc = await sandbox.process.get("dev-server");
const logs = proc.logs; // available if waitForCompletion was true

// Kill a process
await sandbox.process.kill("dev-server");

// Delete the sandbox (all data is erased)
await sandbox.delete();

sandbox = await SandboxInstance.get("my-sandbox")

result = await sandbox.fs.ls("/app")
content = await sandbox.fs.read("/app/src/pages/index.astro")

proc = await sandbox.process.get("dev-server")
# proc.logs available if wait_for_completion was True
await sandbox.process.kill("dev-server")
await sandbox.delete()

Sandbox templates (custom images)

When you need a reusable environment (e.g. an Astro project with all deps pre-installed), create a template:

bl new sandbox my-astro-template
cd my-astro-template

This creates: blaxel.toml, Dockerfile, entrypoint.sh, Makefile.

Customize the Dockerfile. Always include the sandbox-api binary:

FROM node:22-alpine
WORKDIR /app
COPY --from=ghcr.io/blaxel-ai/sandbox:latest /sandbox-api /usr/local/bin/sandbox-api
RUN npm install -g astro
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

The entrypoint.sh must start the sandbox-api:

#!/bin/sh
/usr/local/bin/sandbox-api &
while ! nc -z 127.0.0.1 8080; do sleep 0.1; done
echo "Sandbox API ready"