---
title: "Web SDK vs. DWS Viewer API: Which key do I use?"
canonical_url: "https://www.nutrient.io/guides/web/knowledge-base/web-sdk-vs-dws-viewer/"
md_url: "https://www.nutrient.io/guides/web/knowledge-base/web-sdk-vs-dws-viewer.md"
last_updated: "2026-06-10T21:35:04.317Z"
description: "Resolve 'Could not decode license key' errors by understanding the difference between Web SDK license keys and DWS Viewer API session tokens."
---

A `Could not decode license key` error when using a DWS API key in `NutrientViewer.load()` indicates a product mismatch. DWS Viewer API and Web SDK use different authentication methods.

## Identify your product

| You have...        | Key format                                   | Found in                                  |
| ------------------ | -------------------------------------------- | ----------------------------------------- |
| **DWS Viewer API** | Short API key: `dws_live_abc123...`          | Portal → Document Web Services → API Keys |
| **Web SDK**        | Long license key: `nX5NbnzG...` (500+ chars) | Portal → Manage Licenses                  |

## DWS Viewer API authentication

DWS Viewer API uses **session tokens**, not license keys. The API key authenticates your backend to request session tokens:

```javascript

// ❌ Wrong — API key is not a license key.
NutrientViewer.load({
  container: "#viewer",

  licenseKey: "dws_live_abc123..."  // Error: Could not decode.
});

// ✅ Correct — Use a session token from your backend.
NutrientViewer.load({
  container: "#viewer",

  session: "<session_token_from_backend>"
});

```

Get a session token by calling the DWS API from your server:

```bash

curl -X POST "https://api.nutrient.io/viewer/sessions" \
  -H "Authorization: Bearer dws_live_abc123..." \
  -H "Content-Type: application/json" \
  -d '{"allowed_documents":[{"document_id":"<document_id>","permissions":["read"]}]}'

```

For app-provided documents, omit `allowed_documents` instead:

```bash

curl -X POST "https://api.nutrient.io/viewer/sessions" \
  -H "Authorization: Bearer dws_live_abc123..." \
  -H "Content-Type: application/json" \
  -d '{}'

```

The response contains the session token to pass to the frontend. Do not pass your DWS API key to `NutrientViewer.load()`.

## Web SDK authentication

Web SDK uses a **license key** tied to your domain:

```javascript

NutrientViewer.load({
  container: "#viewer",

  document: "document.pdf",
  licenseKey: "nX5NbnzGFzYhuWTje1LqC8hWYX1jP_WAqka..."
});

```

Get your license key from the [Nutrient Portal](https://my.nutrient.io/) under **Manage Licenses** after registering your domain.

## Quick reference

|                      | DWS Viewer API                                  | Web SDK               |
| -------------------- | ----------------------------------------------- | --------------------- |
| **Authentication**   | Session token (from API)                        | License key (in code) |
| **API key used for** | Backend → DWS API calls                         | Not applicable        |
| **Document source**  | DWS-managed documents or app-provided documents | Your infrastructure   |
| **Rendering**        | DWS Viewer API + Web SDK                        | Client-side Web SDK   |
| **Pricing**          | Usage-based                                     | Per-domain license    |

## Which product do I need?

**Choose DWS Viewer API if**

- You want DWS to manage documents for you

- You want DWS Viewer API session authorization for app-provided documents

- Usage-based pricing works for your scale

- You don’t want to run Document Engine yourself

**Choose Web SDK if**

- Documents stay on your infrastructure

- Client-side rendering is preferred

- Fixed per-domain licensing fits your model

## Additional resources

- [DWS Viewer API documentation](https://www.nutrient.io/api/viewer-api/) — Session tokens and API reference

- [Open PDFs using DWS Viewer API](https://www.nutrient.io/guides/web/open-a-document/from-dws-viewer-api.md) — Frontend integration guide

- [Web SDK licensing](https://www.nutrient.io/guides/web/pspdfkit-for-web/licensing.md) — Domain registration and license keys

- [Ways to use Web SDK](https://www.nutrient.io/guides/web/about/operational-modes.md) — Web SDK deployment options
---

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