# Modal SDK

Modal is a serverless cloud compute platform that allows developers to run code in the cloud without managing infrastructure. The Modal SDKs provide convenient, on-demand access to serverless cloud compute from Python, JavaScript/TypeScript, and Go applications. Core functionality includes creating and managing Sandboxes (isolated container environments), calling deployed Functions, working with persistent storage (Volumes), managing Secrets, and building custom container Images.

The SDKs are designed for a variety of use cases including running AI/ML workloads, executing arbitrary code in isolated environments, building coding agents, and orchestrating distributed computing tasks. The Python SDK (v1.4.2+) is the most feature-complete and allows defining Modal Functions, while the JavaScript (v0.7.4) and Go (v0.7.4) SDKs focus on interacting with deployed resources and creating Sandboxes. All SDKs provide similar APIs for resource management with language-idiomatic patterns.

## Installation

Install the Modal SDK for your language of choice.

```bash
# Python (requires Python 3.10-3.14)
pip install modal
# or
uv pip install modal

# JavaScript/TypeScript (requires Node 22+)
npm install modal

# Go (requires Go 1.23+)
go get -u github.com/modal-labs/modal-client/go
```

## Authentication Setup

Set up Modal authentication via CLI or environment variables.

```bash
# Option 1: Interactive setup (requires Python SDK)
python3 -m modal setup

# Option 2: Environment variables
export MODAL_TOKEN_ID=ak-your-token-id
export MODAL_TOKEN_SECRET=as-your-token-secret

# Optional: Custom config file path
export MODAL_CONFIG_PATH=~/.modal.toml
```

## Creating a Modal Client

Initialize the Modal client to interact with Modal resources.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

// Access Modal resources through the client
const app = await modal.apps.fromName("my-app", { createIfMissing: true });
```

```go
// Go
package main

import (
    "context"
    "log"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, err := modal.NewClient()
    if err != nil {
        log.Fatalf("Failed to create client: %v", err)
    }

    app, err := mc.Apps.FromName(ctx, "my-app", &modal.AppFromNameParams{CreateIfMissing: true})
    if err != nil {
        log.Fatalf("Failed to get or create App: %v", err)
    }
}
```

## Creating a Sandbox

Create an isolated container environment to run arbitrary code. Sandboxes support custom images, GPU access, volumes, secrets, and network configuration.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("sandbox-example", { createIfMissing: true });
const image = modal.images.fromRegistry("alpine:3.21");

const sb = await modal.sandboxes.create(app, image, { command: ["cat"] });
console.log("Sandbox:", sb.sandboxId);

// Write to stdin and read from stdout
await sb.stdin.writeText("Hello from Modal!");
await sb.stdin.close();
console.log("Output:", await sb.stdout.readText());

// Clean up
await sb.terminate();
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    "log"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, err := modal.NewClient()
    if err != nil {
        log.Fatalf("Failed to create client: %v", err)
    }

    app, err := mc.Apps.FromName(ctx, "sandbox-example", &modal.AppFromNameParams{CreateIfMissing: true})
    if err != nil {
        log.Fatalf("Failed to get or create App: %v", err)
    }

    image := mc.Images.FromRegistry("alpine:3.21", nil)

    sb, err := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Command: []string{"cat"},
    })
    if err != nil {
        log.Fatalf("Failed to create Sandbox: %v", err)
    }
    defer sb.Terminate(context.Background(), nil)

    // Write to stdin and read from stdout
    sb.Stdin.Write([]byte("Hello from Modal!"))
    sb.Stdin.Close()

    output, _ := io.ReadAll(sb.Stdout)
    fmt.Printf("Output: %s\n", string(output))
}
```

## Executing Commands in a Sandbox

Execute commands in a running Sandbox and capture stdout/stderr.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("exec-example", { createIfMissing: true });
const image = modal.images.fromRegistry("python:3.13-slim");

const sb = await modal.sandboxes.create(app, image);
console.log("Started Sandbox:", sb.sandboxId);

try {
  const p = await sb.exec(
    ["python", "-c", "print('Hello from Python!')"],
    { stdout: "pipe", stderr: "pipe" }
  );

  const [stdout, stderr] = await Promise.all([
    p.stdout.readText(),
    p.stderr.readText(),
  ]);

  console.log("stdout:", stdout);
  console.log("Return code:", await p.wait());
} finally {
  await sb.terminate();
}
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    "log"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "exec-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("python:3.13-slim", nil)

    sb, _ := mc.Sandboxes.Create(ctx, app, image, nil)
    defer sb.Terminate(context.Background(), nil)

    p, _ := sb.Exec(ctx, []string{"python", "-c", "print('Hello from Python!')"}, nil)

    stdout, _ := io.ReadAll(p.Stdout)
    fmt.Printf("stdout: %s", string(stdout))

    returnCode, _ := p.Wait(ctx)
    fmt.Println("Return code:", returnCode)
}
```

## Calling Deployed Functions

Look up and call Functions that have been deployed to Modal using the Python SDK.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

// Look up a deployed function by app name and function name
const echo = await modal.functions.fromName("my-app", "echo_string");

// Call with positional arguments
let result = await echo.remote(["Hello world!"]);
console.log(result);

// Call with keyword arguments
result = await echo.remote([], { s: "Hello world!" });
console.log(result);
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "log"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    // Look up a deployed function
    echo, err := mc.Functions.FromName(ctx, "my-app", "echo_string", nil)
    if err != nil {
        log.Fatalf("Failed to get Function: %v", err)
    }

    // Call with positional arguments
    ret, _ := echo.Remote(ctx, []any{"Hello world!"}, nil)
    fmt.Println("Response:", ret)

    // Call with keyword arguments
    ret, _ = echo.Remote(ctx, nil, map[string]any{"s": "Hello world!"})
    fmt.Println("Response:", ret)
}
```

## Spawning Functions Asynchronously

Spawn a Function call and retrieve results later.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const echo = await modal.functions.fromName("my-app", "echo_string");

// Spawn the Function asynchronously
const functionCall = await echo.spawn([], { s: "Hello world!" });

// Do other work...

// Get the result when ready
const result = await functionCall.get();
console.log(result);
```

```go
// Go
package main

import (
    "context"
    "fmt"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    echo, _ := mc.Functions.FromName(ctx, "my-app", "echo_string", nil)

    // Spawn the Function asynchronously
    fc, _ := echo.Spawn(ctx, nil, map[string]any{"s": "Hello world!"})

    // Get the result when ready
    ret, _ := fc.Get(ctx, nil)
    fmt.Println("Response:", ret)
}
```

## Calling Modal Classes (Cls)

Instantiate and call methods on Modal Classes deployed via the Python SDK.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

// Look up a deployed class
const cls = await modal.cls.fromName("my-app", "MyClass");
const instance = await cls.instance();
const method = instance.method("process");

// Call the class method
let result = await method.remote(["input data"]);
console.log(result);

// Call with keyword arguments
result = await method.remote([], { data: "input data" });
console.log(result);
```

```go
// Go
package main

import (
    "context"
    "fmt"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    // Look up a deployed class
    cls, _ := mc.Cls.FromName(ctx, "my-app", "MyClass", nil)
    instance, _ := cls.Instance(ctx, nil)
    method, _ := instance.Method("process")

    // Call the class method
    result, _ := method.Remote(ctx, []any{"input data"}, nil)
    fmt.Println("Response:", result)
}
```

## Working with Volumes

Mount persistent Volumes to Sandboxes for data sharing and persistence.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("volume-example", { createIfMissing: true });
const image = modal.images.fromRegistry("alpine:3.21");

// Create or get an existing volume
const volume = await modal.volumes.fromName("my-volume", { createIfMissing: true });

// Writer sandbox - mounts volume with read/write access
const writer = await modal.sandboxes.create(app, image, {
  command: ["sh", "-c", "echo 'Hello from writer!' > /mnt/volume/message.txt"],
  volumes: { "/mnt/volume": volume },
});
await writer.wait();
console.log("Writer finished");

// Reader sandbox - mounts volume as read-only
const reader = await modal.sandboxes.create(app, image, {
  volumes: { "/mnt/volume": volume.readOnly() },
});

const proc = await reader.exec(["cat", "/mnt/volume/message.txt"]);
console.log("Reader output:", await proc.stdout.readText());

await writer.terminate();
await reader.terminate();
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "volume-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("alpine:3.21", nil)

    // Create or get an existing volume
    volume, _ := mc.Volumes.FromName(ctx, "my-volume", &modal.VolumeFromNameParams{CreateIfMissing: true})

    // Writer sandbox
    writer, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Command: []string{"sh", "-c", "echo 'Hello from writer!' > /mnt/volume/message.txt"},
        Volumes: map[string]*modal.Volume{"/mnt/volume": volume},
    })
    writer.Wait(ctx)
    defer writer.Terminate(context.Background(), nil)

    // Reader sandbox with read-only volume
    reader, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Volumes: map[string]*modal.Volume{"/mnt/volume": volume.ReadOnly()},
    })
    defer reader.Terminate(context.Background(), nil)

    proc, _ := reader.Exec(ctx, []string{"cat", "/mnt/volume/message.txt"}, nil)
    output, _ := io.ReadAll(proc.Stdout)
    fmt.Printf("Reader output: %s", string(output))
}
```

## Working with Secrets

Inject secrets as environment variables into Sandboxes.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("secrets-example", { createIfMissing: true });
const image = modal.images.fromRegistry("alpine:3.21");

// Get a named secret from Modal
const namedSecret = await modal.secrets.fromName("my-api-key", {
  requiredKeys: ["API_KEY"],
});

// Create an ephemeral secret from key-value pairs
const ephemeralSecret = await modal.secrets.fromObject({
  DATABASE_URL: "postgres://localhost/mydb",
});

const sb = await modal.sandboxes.create(app, image, {
  command: ["sh", "-lc", "printenv | grep -E '^API_KEY|DATABASE_URL='"],
  secrets: [namedSecret, ephemeralSecret],
});

console.log("Environment variables:");
console.log(await sb.stdout.readText());

await sb.terminate();
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "secrets-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("alpine:3.21", nil)

    // Get a named secret
    namedSecret, _ := mc.Secrets.FromName(ctx, "my-api-key", &modal.SecretFromNameParams{
        RequiredKeys: []string{"API_KEY"},
    })

    // Create an ephemeral secret
    ephemeralSecret, _ := mc.Secrets.FromMap(ctx, map[string]string{
        "DATABASE_URL": "postgres://localhost/mydb",
    }, nil)

    sb, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Command: []string{"sh", "-lc", "printenv | grep -E '^API_KEY|DATABASE_URL='"},
        Secrets: []*modal.Secret{namedSecret, ephemeralSecret},
    })
    defer sb.Terminate(context.Background(), nil)

    output, _ := io.ReadAll(sb.Stdout)
    fmt.Printf("Environment variables:\n%s", string(output))
}
```

## Building Custom Images

Build custom container images with Dockerfile commands and secrets.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("image-example", { createIfMissing: true });

// Build a custom image with Dockerfile commands
const image = modal.images
  .fromRegistry("alpine:3.21")
  .dockerfileCommands(["RUN apk add --no-cache curl=$CURL_VERSION"], {
    secrets: [
      await modal.secrets.fromObject({ CURL_VERSION: "8.12.1-r1" }),
    ],
  })
  .dockerfileCommands(["ENV SERVER=ipconfig.me"]);

const sb = await modal.sandboxes.create(app, image, {
  command: ["sh", "-c", "curl -Ls $SERVER"],
});

console.log("Output:", await sb.stdout.readText());
await sb.terminate();
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "image-example", &modal.AppFromNameParams{CreateIfMissing: true})

    // Create a secret for build-time use
    secret, _ := mc.Secrets.FromMap(ctx, map[string]string{
        "CURL_VERSION": "8.12.1-r1",
    }, nil)

    // Build a custom image
    image := mc.Images.FromRegistry("alpine:3.21", nil).
        DockerfileCommands([]string{"RUN apk add --no-cache curl=$CURL_VERSION"}, &modal.ImageDockerfileCommandsParams{
            Secrets: []*modal.Secret{secret},
        }).
        DockerfileCommands([]string{"ENV SERVER=ipconfig.me"}, nil)

    sb, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Command: []string{"sh", "-c", "curl -Ls $SERVER"},
    })
    defer sb.Terminate(context.Background(), nil)

    output, _ := io.ReadAll(sb.Stdout)
    fmt.Println("Output:", string(output))
}
```

## Creating Sandboxes with GPU

Create Sandboxes with GPU acceleration for ML/AI workloads.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("gpu-example", { createIfMissing: true });
const image = modal.images.fromRegistry("nvidia/cuda:12.4.0-devel-ubuntu22.04");

// Create a Sandbox with an A10G GPU
const sb = await modal.sandboxes.create(app, image, { gpu: "A10G" });
console.log("Started Sandbox with A10G GPU:", sb.sandboxId);

try {
  const gpuCheck = await sb.exec(["nvidia-smi"]);
  console.log(await gpuCheck.stdout.readText());
} finally {
  await sb.terminate();
}
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "gpu-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("nvidia/cuda:12.4.0-devel-ubuntu22.04", nil)

    // Create a Sandbox with GPU
    sb, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        GPU: "A10G",  // Options: "T4", "A10G", "A100", "A100-80GB", "H100", etc.
    })
    defer sb.Terminate(context.Background(), nil)

    p, _ := sb.Exec(ctx, []string{"nvidia-smi"}, nil)
    output, _ := io.ReadAll(p.Stdout)
    fmt.Printf("%s\n", string(output))
}
```

## Exposing Ports with Tunnels

Expose TCP ports from a Sandbox via secure tunnels.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("tunnel-example", { createIfMissing: true });
const image = modal.images.fromRegistry("python:3.12-alpine");

// Create a Sandbox with an HTTP server and expose port 8000
const sb = await modal.sandboxes.create(app, image, {
  command: ["python3", "-m", "http.server", "8000"],
  encryptedPorts: [8000],
  timeoutMs: 60000,
  idleTimeoutMs: 30000,
});

// Wait for server to start
await new Promise((resolve) => setTimeout(resolve, 3000));

// Get tunnel information
const tunnels = await sb.tunnels();
const tunnel = tunnels[8000];

console.log("Tunnel URL:", tunnel.url);

// Make a request to the tunneled server
const response = await fetch(tunnel.url);
console.log("Response:", await response.text());

await sb.terminate();
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    "net/http"
    "time"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "tunnel-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("python:3.12-alpine", nil)

    sb, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Command:        []string{"python3", "-m", "http.server", "8000"},
        EncryptedPorts: []int{8000},
        Timeout:        1 * time.Minute,
        IdleTimeout:    30 * time.Second,
    })
    defer sb.Terminate(context.Background(), nil)

    time.Sleep(3 * time.Second)

    tunnels, _ := sb.Tunnels(ctx, 30*time.Second)
    tunnel := tunnels[8000]

    fmt.Println("Tunnel URL:", tunnel.URL())

    resp, _ := http.Get(tunnel.URL())
    defer resp.Body.Close()
    body, _ := io.ReadAll(resp.Body)
    fmt.Printf("Response:\n%s\n", string(body))
}
```

## Filesystem Operations

Read and write files directly in a Sandbox filesystem.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("fs-example", { createIfMissing: true });
const image = modal.images.fromRegistry("alpine:3.21");

const sb = await modal.sandboxes.create(app, image);

try {
  const encoder = new TextEncoder();
  const decoder = new TextDecoder();

  // Write a file
  const writeHandle = await sb.open("/tmp/example.txt", "w");
  await writeHandle.write(encoder.encode("Hello, Modal filesystem!\n"));
  await writeHandle.write(encoder.encode("Line 2\n"));
  await writeHandle.close();

  // Read the file
  const readHandle = await sb.open("/tmp/example.txt", "r");
  const content = await readHandle.read();
  console.log("File content:", decoder.decode(content));
  await readHandle.close();

  // Append to the file
  const appendHandle = await sb.open("/tmp/example.txt", "a");
  await appendHandle.write(encoder.encode("Appended line\n"));
  await appendHandle.close();
} finally {
  await sb.terminate();
}
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "fs-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("alpine:3.21", nil)

    sb, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{})
    defer sb.Terminate(context.Background(), nil)

    // Write a file
    writeFile, _ := sb.Open(ctx, "/tmp/example.txt", "w")
    writeFile.Write([]byte("Hello, Modal filesystem!\n"))
    writeFile.Close()

    // Read the file
    reader, _ := sb.Open(ctx, "/tmp/example.txt", "r")
    content, _ := io.ReadAll(reader)
    fmt.Printf("File content:\n%s\n", string(content))
    reader.Close()
}
```

## Snapshotting Sandbox Filesystem

Create an image snapshot from a Sandbox's filesystem state.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("snapshot-example", { createIfMissing: true });
const baseImage = modal.images.fromRegistry("alpine:3.21");

// Create first sandbox and set up state
const sb = await modal.sandboxes.create(app, baseImage);
await sb.exec(["mkdir", "-p", "/app/data"]);
await sb.exec(["sh", "-c", "echo 'Snapshot data' > /app/data/info.txt"]);

// Create a snapshot of the filesystem
const snapshotImage = await sb.snapshotFilesystem();
console.log("Snapshot Image ID:", snapshotImage.imageId);
await sb.terminate();

// Create a new sandbox from the snapshot
const sb2 = await modal.sandboxes.create(app, snapshotImage);
const proc = await sb2.exec(["cat", "/app/data/info.txt"]);
console.log("Data from snapshot:", await proc.stdout.readText());
await sb2.terminate();
```

```go
// Go
package main

import (
    "context"
    "fmt"
    "io"
    "time"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "snapshot-example", &modal.AppFromNameParams{CreateIfMissing: true})
    baseImage := mc.Images.FromRegistry("alpine:3.21", nil)

    // Create and set up first sandbox
    sb, _ := mc.Sandboxes.Create(ctx, app, baseImage, &modal.SandboxCreateParams{})
    sb.Exec(ctx, []string{"mkdir", "-p", "/app/data"}, nil)
    sb.Exec(ctx, []string{"sh", "-c", "echo 'Snapshot data' > /app/data/info.txt"}, nil)

    // Create filesystem snapshot
    snapshotImage, _ := sb.SnapshotFilesystem(ctx, 55*time.Second)
    fmt.Printf("Snapshot Image ID: %s\n", snapshotImage.ImageID)
    sb.Terminate(ctx, nil)

    // Create new sandbox from snapshot
    sb2, _ := mc.Sandboxes.Create(ctx, app, snapshotImage, nil)
    defer sb2.Terminate(context.Background(), nil)

    proc, _ := sb2.Exec(ctx, []string{"cat", "/app/data/info.txt"}, nil)
    content, _ := io.ReadAll(proc.Stdout)
    fmt.Printf("Data from snapshot: %s", string(content))
}
```

## Polling Sandbox Status

Check if a Sandbox is still running and get its exit code.

```typescript
// JavaScript/TypeScript
import { ModalClient } from "modal";

const modal = new ModalClient();

const app = await modal.apps.fromName("poll-example", { createIfMissing: true });
const image = modal.images.fromRegistry("alpine:3.21");

// Create a sandbox that waits for input then exits with code 42
const sb = await modal.sandboxes.create(app, image, {
  command: ["sh", "-c", "read line; exit 42"],
});

// Poll returns undefined while running
console.log("Poll while running:", await sb.poll());

// Send input to trigger completion
await sb.stdin.writeText("done");
await sb.stdin.close();

// Wait for completion and get exit code
const exitCode = await sb.wait();
console.log("Exit code:", exitCode);

// Poll returns exit code after completion
console.log("Poll after completion:", await sb.poll());
```

```go
// Go
package main

import (
    "context"
    "fmt"
    modal "github.com/modal-labs/modal-client/go"
)

func main() {
    ctx := context.Background()
    mc, _ := modal.NewClient()

    app, _ := mc.Apps.FromName(ctx, "poll-example", &modal.AppFromNameParams{CreateIfMissing: true})
    image := mc.Images.FromRegistry("alpine:3.21", nil)

    sb, _ := mc.Sandboxes.Create(ctx, app, image, &modal.SandboxCreateParams{
        Command: []string{"sh", "-c", "read line; exit 42"},
    })
    defer sb.Terminate(context.Background(), nil)

    // Poll returns nil while running
    initialPoll, _ := sb.Poll(ctx)
    fmt.Printf("Poll while running: %v\n", initialPoll)

    // Send input to trigger completion
    sb.Stdin.Write([]byte("done\n"))
    sb.Stdin.Close()

    exitCode, _ := sb.Wait(ctx)
    fmt.Printf("Exit code: %d\n", exitCode)

    // Poll returns exit code after completion
    finalPoll, _ := sb.Poll(ctx)
    fmt.Printf("Poll after completion: %d\n", *finalPoll)
}
```

## Python SDK - Defining Functions

Define serverless functions using the Python SDK (functions can then be called from any SDK).

```python
# Python
import modal

app = modal.App("my-app")

@app.function()
def echo_string(s: str) -> str:
    """Echo the input string back."""
    return f"Echo: {s}"

@app.function(gpu="A10G")
def run_inference(prompt: str) -> str:
    """Run ML inference with GPU acceleration."""
    # Your ML code here
    return f"Result for: {prompt}"

# Deploy with: modal deploy my_app.py
```

## Python SDK - Defining Classes

Define stateful classes with the Python SDK for persistent instances.

```python
# Python
import modal

app = modal.App("my-app")

@app.cls(gpu="T4")
class MyModel:
    @modal.enter()
    def load_model(self):
        # Load model once when container starts
        self.model = load_my_model()

    @modal.method()
    def predict(self, input_data: str) -> str:
        return self.model.predict(input_data)

# Deploy with: modal deploy my_app.py
# Then call from JS/Go using modal.cls.fromName()
```

## Python SDK - Creating Sandboxes

Create and interact with Sandboxes directly in Python.

```python
# Python
import modal

app = modal.App.lookup("sandbox-example", create_if_missing=True)

# Create a sandbox
sandbox = modal.Sandbox.create(
    "python", "-c", "print('Hello from sandbox!')",
    image=modal.Image.debian_slim().pip_install("numpy"),
    timeout=300,
    app=app,
)

# Read output
print(sandbox.stdout.read())

# Execute additional commands
proc = sandbox.exec("python", "-c", "import numpy; print(numpy.__version__)")
print(proc.stdout.read())

# Clean up
sandbox.terminate()
```

## Python SDK - Readiness Probes

Configure readiness probes to wait for Sandboxes to be ready.

```python
# Python
import modal

app = modal.App.lookup("probe-example", create_if_missing=True)

# Wait until a TCP port is accepting connections
tcp_probe = modal.Probe.with_tcp(8080)

# Or wait until a command succeeds
exec_probe = modal.Probe.with_exec("sh", "-c", "test -f /tmp/ready")

sandbox = modal.Sandbox.create(
    "python", "-m", "http.server", "8080",
    readiness_probe=tcp_probe,
    app=app,
)

# Block until the probe succeeds
sandbox.wait_until_ready()
print("Server is ready!")

sandbox.terminate()
```

## Summary

The Modal SDKs enable developers to leverage serverless cloud computing across Python, JavaScript/TypeScript, and Go applications. The primary use cases include: running AI/ML inference with GPU acceleration, executing untrusted code in isolated Sandboxes, building AI coding agents, orchestrating distributed compute jobs, and creating custom container-based workflows. The SDKs provide a unified interface for managing cloud resources including Functions, Classes, Sandboxes, Volumes, Secrets, and Images.

Integration patterns typically involve deploying Functions and Classes using the Python SDK, then calling them from any language using the JS/Go SDKs. Sandboxes are commonly used for agent-based systems where arbitrary code execution is required. All SDKs support volume mounting for persistent storage, secret injection for credentials, custom image building, and network tunneling for exposing services. The APIs follow language-idiomatic conventions while maintaining consistent functionality across all three SDKs, making it easy to integrate Modal into polyglot architectures.