 Alexandra Klepper [GitHub](https://github.com/alexandrascript) [Bluesky](https://bsky.app/profile/alexandrascript.com)  Thomas Steiner [GitHub](https://github.com/tomayac) [LinkedIn](https://www.linkedin.com/in/thomassteinerlinkedin) [Mastodon](https://toot.cafe/@tomayac) [Bluesky](https://bsky.app/profile/tomayac.com) [Homepage](https://blog.tomayac.com/)
Published: October 22, 2025
| Explainer | Web | Extensions | Chrome Status | Intent |
|---|---|---|---|---|
| [GitHub](https://github.com/explainers-by-googlers/writing-assistance-apis/) |  Developer trial |  Developer trial | [View](https://chromestatus.com/feature/4712595362414592) | [Intent to Experiment](https://groups.google.com/a/chromium.org/g/blink-dev/c/HCSzUSI8kI8/m/A3I4o5YlBAAJ) |
The Writer API helps you create new content that conforms to a specified writing
task. The Writer API and the [Rewriter API](https://developer.chrome.com/docs/ai/rewriter) are part of the
[Writing Assistance APIs proposal](https://github.com/explainers-by-googlers/writing-assistance-apis/).
These partner APIs can help you improve content created by users.
> [!IMPORTANT]
> **Important** : The built-in foundation model is a generative AI model. Before you build with APIs that use it, you should review the [People + AI Guidebook](https://pair.withgoogle.com/guidebook/) for best practices, methods, and examples for designing with AI.
## Use cases
Write new content, based on your initial idea and optional context. This could
be used to:
- Support users write any kind of content, like reviews, blog posts, or emails.
- Help users write better support requests.
- Draft an introduction for a series of work samples, to better capture certain skills.
Is your use case missing? Join the [early preview program](https://developer.chrome.com/docs/ai/join-epp)
to share your feedback.
## Get started
[Join the Writer API origin trial](https://developer.chrome.com/docs/ai/writer-api#origin-trial) running in Chrome 137 to 148.
### Review the hardware requirements
The following requirements exist for developers and the users who operate features using these
APIs in Chrome. Other browsers may have different operating requirements.
The **Language Detector** and **Translator APIs** work in Chrome on
desktop. These APIs do not work on mobile devices.
The **Prompt API** , **Summarizer API** , **Writer API** ,
**Rewriter API** , and **Proofreader API** work in Chrome when the
following conditions are met:
- **Operating system** : Windows 10 or 11; macOS 13+ (Ventura and onwards); Linux; or ChromeOS (from Platform 16389.0.0 and onwards) on [Chromebook Plus](https://www.google.com/chromebook/chromebookplus/) devices. Chrome for Android, iOS, and ChromeOS on non-Chromebook Plus devices are not yet supported by the APIs which use foundation models.
- **Storage** : At least 22 GB of free space on the volume that contains your Chrome profile.
> [!NOTE]
> Built-in models should be significantly smaller. The exact size may vary slightly with updates.
- **GPU or CPU** : Built-in models can run with GPU or CPU.
- **GPU**: Strictly more than 4 GB of VRAM.
- **CPU**: 16 GB of RAM or more and 4 CPU cores or more.
- **Note**: The Prompt API with audio input requires a GPU.
- **Network** : Unlimited data or an unmetered connection.
> [!IMPORTANT]
> **Key term** : A [metered connection](https://support.microsoft.com/windows/metered-connections-in-windows-7b33928f-a144-b265-97b6-f2e95a87c408) is a data-limited internet connection. Wi-Fi and ethernet connections tend to be unmetered by default, while cellular connections are often metered.
> [!NOTE]
> **Note**: The network requirement is only for the initial download of the model. Subsequent use of the model does not require a network connection. No data is sent to Google or any third party when using the model.
Gemini Nano's exact size may vary as the browser updates the model. To determine the current size, visit `chrome://on-device-internals`.
> [!NOTE]
> **Note**: If the available storage space falls to less than 10 GB after the download, the model is removed from your device. The model redownloads once the requirements are met.
### Sign up for the origin trial
The Writer API is available in a joint origin trial with the Rewriter API. To
start using these APIs:
1. Go to the [Writer API origin trial](https://developer.chrome.com/origintrials#/view_trial/-8779204523605360639).
2. Click **Register** and fill out the form. In the Web origin field, provide your [origin](https://web.dev/articles/same-site-same-origin#origin) or extension ID, `chrome-extension://YOUR_EXTENSION_ID`.
3. To submit, click **Register**.
4. Copy the token provided, and add it to every participating web page on your origin or include it in [your Extension manifest](https://developer.chrome.com/docs/web-platform/origin-trials#extensions).
5. Start using the Writer and Rewriter APIs.
Learn more about how to [get started with origin trials](https://developer.chrome.com/docs/web-platform/origin-trials).
### Add support to localhost
To access the Writer API on localhost, use
[Chrome flags](https://developer.chrome.com/docs/web-platform/chrome-flags):
1. Set the `chrome://flags/#writer-api` flag to **Enabled** or **Enabled Multilingual**.
2. Click **Relaunch** or restart Chrome.
## Use the Writer API
First, run feature detection to see if the browser supports these APIs.
if ('Writer' in self) {
// The Writer API is supported.
}
> [!TIP]
> **Tip:** Use the [@types/dom-chromium-ai](https://www.npmjs.com/package/@types/dom-chromium-ai) npm package to get TypeScript typings for the Prompt API and other built-in AI APIs for easier access in your codebase.
The Writer API, and all other built-in AI APIs, are integrated in the browser.
The model is downloaded separately the first time any website uses a built-in
AI API. In practice, if a user has already interacted with a built-in API, they
have downloaded the model to their browser.
To determine if the model is ready to use, call the asynchronous
[`Writer.availability()`](https://developer.chrome.com/docs/ai/get-started#model-download) function. If
the response to `availability()` is `downloadable`, listen for download progress
and inform the user, as the download may take time.
const availability = await Writer.availability();
To trigger model download and start the writer, check for
[user activation](https://developer.chrome.com/docs/ai/get-started#user-activation)
and call the `Writer.create()` function.
const writer = await Writer.create({
monitor(m) {
m.addEventListener("downloadprogress", e => {
console.log(`Downloaded ${e.loaded * 100}%`);
});
}
});
### API functions
The `create()` function lets you configure a new writer object. It takes an
optional `options` object with the following parameters:
- `tone`: [Writing tone](https://owl.purdue.edu/owl/multilingual/multilingual_students/key_concepts_for_writing_in_north_american_colleges/style_genre_and_writing.html) can refer to the style, character, or attitude of the content. The value can be set to `formal`, `neutral` (default), or `casual`.
- `format`: The output formatting, with the allowed values `markdown` (default) and `plain-text`.
- `length`: The length of the output, with the allowed values `short` (default), `medium`, and `long`.
- `sharedContext`: When writing [multiple outputs](https://developer.chrome.com/docs/ai/writer-api#multiple-tasks), a shared context can help the model create content better aligned with your expectations.
> [!NOTE]
> **Note:** Once set, the parameters can't be changed. Create a new writer object if you need to modify the parameters.
The following example demonstrates how to initiate a `writer` object:
const options = {
sharedContext: 'This is an email to acquaintances about an upcoming event.',
tone: 'casual',
format: 'plain-text',
length: 'medium',
};
const available = await Writer.availability();
let writer;
if (available === 'unavailable') {
// The Writer API isn't usable.
return;
}
if (available === 'available') {
// The Writer API can be used immediately .
writer = await Writer.create(options);
} else {
// The Writer can be used after the model is downloaded.
const writer = await Writer.create({
...options,
monitor(m) {
m.addEventListener("downloadprogress", e => {
console.log(`Downloaded ${e.loaded * 100}%`);
});
}
});
}
### Assign expected languages
The Writer API supports multiple languages. Set the expected input and context
languages as well as the expected output language when creating your session.
This allows the browser to reject the request if the
browser cannot support a specific language combination.
const writer = await Writer.create({
tone: "formal",
expectedInputLanguages: ["en", "ja", "es"],
expectedContextLanguages: ["en", "ja", "es"],
outputLanguage: "es",
sharedContext: "These are requests to write messages to teachers in a Spanish
language program, by students who may speak Spanish, Japanese, or English.
Staff expect questions to be written in Spanish."
});
### Start writing
There are two ways to output writing from the model: request-based output and
streaming.
#### Request-based output
For request-based output (or "non-streaming"), the model waits for the entire
input to be generated, process that input as a whole, and then produces
the output.
To get a request-based output, call the asynchronous `write()` function. You
must include a prompt for the content you want written. You can add an optional
`context` to provide the model background information, which may help the model
better meet your expectations for the output.
// Request-based
const writer = await Writer.create();
const result = await writer.write(
"An inquiry to my bank about how to enable wire transfers on my account.",
{
context: "I'm a longstanding customer",
},
);
#### Stream writing output
Streaming offers continuous results, in real-time. The output updates
incrementally, as input is added and adjusted.
To get a streaming writer, call the `writeStreaming()` function and iterate
over the available segments of text in the stream. You can add an optional
`context` to provide the model background information, which may help the model
better meet your expectations for the output.
// Streaming
const writer = await Writer.create(
expectedInputLanguages: ["en"],
expectedContextLanguages: ["en"],
outputLanguage: "en",
);
const stream = writer.writeStreaming(
"An inquiry to my bank about how to enable wire transfers on my account.", {
context: "I'm a longstanding customer",
},
);
for await (const chunk of stream) {
composeTextbox.append(chunk);
}
#### Share context for multiple tasks
You may want to use a `writer` to generate multiple pieces of content. In this
case, it's useful to add `sharedContext`. For example, you may want to help
reviewers give better feedback in comments.
// Shared context and per writing task context
const writer = await Writer.create({
expectedInputLanguages: ["en"],
expectedContextLanguages: ["en"],
outputLanguage: "en",
sharedContext:
"This is for publishing on [popular website name], a business" +
"and employment-focused social media platform."
});
const stream = writer.writeStreaming(
"Write a blog post about how I love all this work on gen AI at Google!" +
"Mention that there's so much to learn and so many new things I can do!",
{ context: " The request comes from someone working at a startup providing an e-commerce CMS solution."}
);
for await (const chunk of stream) {
composeTextbox.append(chunk);
}
#### Reuse a writer
You can use the same writer to create multiple pieces of content.
// Reuse a writer
const writer = await Writer.create({ tone: "formal" });
const reviews = await Promise.all(
Array.from(
document.querySelectorAll("#reviews > .review"),
(reviewEl) => writer.write(reviewEl.textContent)
),
);
#### Stop the writer
To end the writing process, abort the controller and destroy the writer.
// Aborting a writer
const controller = new AbortController();
stopButton.onclick = () => controller.abort();
const writer = await Writer.create({ signal: controller.signal });
await writer.write(reviewEl.textContent, { signal: controller.signal });
// Destroying a writer
writer.destroy();
## Demo
## Permission Policy, iframes, and Web Workers
By default, the Writer API is only available to top-level windows and to their
same-origin iframes. Access to the API can be delegated to cross-origin iframes
using the Permission Policy `allow=""` attribute:
The Writer API isn't available in Web Workers. This is due to the
complexity of establishing a responsible document for each worker in order to
check the Permissions Policy status.
## Engage and share feedback
The Writer and [Rewriter API](https://developer.chrome.com/docs/ai/rewriter-api) are under active discussion
and subject to change in the future. If you try this API and have feedback,
we'd love to hear it.
- [Read the explainer](https://github.com/explainers-by-googlers/writing-assistance-apis/), raise questions and participate in discussion.
- [Review Chrome Status](https://chromestatus.com/feature/4712595362414592) for updates on the API's implementation in Chrome.
- If you have feedback on Chrome's implementation, file a [Chromium bug](https://new.crbug.com/).
- [Join the early preview program](https://developer.chrome.com/docs/ai/join-epp) for an early look at new APIs and access to our mailing list.
Discover all of the [built-in AI APIs](https://developer.chrome.com/docs/ai/built-in-apis) which use
foundation and expert models in the browser.