Summarizer

The Summarizer API allows web developers to offer local, AI-powered text distillation directly within the browser using Gemini Nano in Chrome or Phi in Edge. This API supports various formats, including key points, headlines, and TL;DRs, while operating entirely on-device to ensure user privacy.

Getting Started

The Summarizer API is available starting in Chrome and Edge 138. It requires a one-time model download of Gemini Nano or Phi (respectively).

Hardware & Software Requirements

• OS: Windows 10/11, macOS 13+, Linux, or ChromeOS (Chromebook Plus).
• Storage: 22GB free space for the profile volume.
• RAM/CPU: 16GB+ RAM and 4+ CPU cores.
• VRAM: 4GB+ (if using GPU).

Model Download and Availability

Check if the model is ready, needs downloading, or is unavailable.

Mandatory Options Passing: You must pass the identical configuration options object to both Summarizer.availability(options) and Summarizer.create(options). Do NOT use the deprecated window.ai.summarizer API surface.

Mandatory Progress Monitoring: You MUST implement a monitor for model download progress by providing a monitor(m) callback to Summarizer.create() and adding a listener for the downloadprogress event.

User Gesture Requirement: When availability is 'downloadable' or 'downloading', triggering the actual download via Summarizer.create() requires a user gesture (such as a user click). You must place the creation call inside an event listener rather than calling it unconditionally on page load to prevent NotAllowedError.

const options = {
  type: 'key-points',
  format: 'plain-text',
  length: 'medium'
};

const availability = await Summarizer.availability(options);

if (availability === 'available') {
  const summarizer = await Summarizer.create(options);
  // Ready to use immediately
} else if (availability === 'downloadable') {
  // A user gesture is strictly required to start the download
  document.getElementById('start-download-btn').addEventListener('click', async () => {
    const summarizer = await Summarizer.create({
      ...options,
      monitor(m) {
        m.addEventListener('downloadprogress', (e) => {
          console.log(`Downloaded ${Math.round((e.loaded / e.total) * 100)}%`);
        });
      },
    });
  });
}

API Functions & Configuration

When creating a summarizer via Summarizer.create(options), you can customize the output:

Example Configuration

const options = {
  sharedContext: 'This is a scientific article',
  type: 'key-points',
  format: 'markdown',
  length: 'medium',
};

if (navigator.userActivation.isActive) {
  const summarizer = await Summarizer.create(options);
}

Language Support

You can specify expected languages to ensure the browser can handle the specific summary request.

const summarizer = await Summarizer.create({
  type: 'key-points',
  expectedInputLanguages: ['en', 'ja'],
  outputLanguage: 'es',
});

Summarization Methods

1. Batch Summarization

Processes the entire text at once and returns the result.

const longText = document.querySelector('article').innerText;
const summary = await summarizer.summarize(longText, {
  context: 'This article is intended for a tech-savvy audience.',
});
console.log(summary);

2. Stream Summarization

Returns results in real-time as the model generates them, providing a more responsive UI.

const stream = summarizer.summarizeStreaming(longText);
for await (const chunk of stream) {
  console.log(chunk);
}

Security and Permissions

• Data Privacy: No data is sent to Google; processing happens on the local device.

• Cross-Origin: Access can be granted to iframes using the Permission Policy.

  <iframe src="https://example.com/" allow="summarizer"></iframe>
  

• Web Workers: Currently not supported.

Fallback Strategy

Before initializing or querying availability, check if the browser supports the Summarizer API:

if ('Summarizer' in self) {
  // The Summarizer API is supported.
} else {
  // Execute fallback strategy
}

If the Summarizer API is unsupported or availability checks return 'unavailable', you must gracefully fall back.

Recommended options:

1. Remote API Fallback: Direct the distillation request to a server endpoint or remote API (such as the Vertex AI Gemini API) so that users still get summaries.
2. Graceful Degradation: Visually disable the summarization controls in the UI, or hide the button while displaying a friendly message (e.g., "Local summarization is currently unsupported in this browser"). Do not allow interaction to trigger generic unhandled runtime exceptions.
3. Polyfill Fallback: You can use community-maintained polyfills like built-in-ai-task-apis-polyfills or prompt-api-polyfill to emulate the API surface using remote services with models in the cloud or on-device inference with local models.

Privacy and Cost Implications: These polyfills possibly proxy requests to remote servers (such as Gemini API over the cloud). This completely nullifies the on-device privacy guarantees of the native Built-in AI APIs and will incur server-side API usage costs.