Chrome Proofreader API Download Stuck at 0%

[Bryan Dhaniel]

Hey everyone,

I'm trying to use the Chrome Proofreader API, but the model download is always stuck at 0%. Other APIs like Summarizer and Translator are working fine in my project.

I've already checked chrome://on-device-internals/, and the status for ProofreaderApi shows Version: 0.

My questions are:

1. Is this likely related to an Origin Trial Token?

2. For development on localhost, is enabling the chrome://flags/#proofreader-api-for-gemini-nano flag enough, or is a token still required?

3. If I have a token for a Vercel domain, will it also work for localhost?

Thanks!

 react-dom-client.development.js:25630 Download the React DevTools for a better development experience: https://react.dev/link/react-devtools (index):1 No output language was specified in a Summarizer API request. An output language should be specified to ensure optimal output quality and properly attest to output safety. Please specify a supported output language code: [en, es, ja] page.tsx:56 Summarizer availability: available page.tsx:60 Translator API supported page.tsx:64 Translator availability (en->id): available page.tsx:71 Proofreader API supported page.tsx:74 Proofreader availability: downloadable page.tsx:77 ⚠️ Proofreader model needs to be downloaded. It will download on first use. StudyMindApp.useEffect.checkSupport @ page.tsx:77 turbopack-hot-reloader-common.ts:43 [Fast Refresh] rebuilding report-hmr-latency.ts:26 [Fast Refresh] done in 404ms page.tsx:218 Starting proofreading with options: Object page.tsx:219 Calling proofread API with progress tracking...
Overall proofreading timeout after 5 minutes
error @ intercept-console-error.ts:44
(anonymous) @ page.tsx:224Understand this error
page.tsx:282 AI proofreading error: Error: Proofreading timeout (5 minutes) - Model download may still be in progress. Check chrome://on-device-internals/ for download status.
    at page.tsx:225:18

[Thomas Steiner]

Hi Bryan,

The Proofreader API and the Summarizer API both depend on Gemini Nano, so if the Summarizer API is working for you, it means that the base model is downloaded correctly. The Proofreader API on top depends on LoRA, so likely the download is stalled there. Could I ask you to paste the result of these two calls into your next reply? Also, what is the output of `chrome://version` (put this in the URL bar and press return)?

await Proofreader.availability({

  expectedInputLanguages: ['en'],

  correctionExplanationLanguage: 'en',

  includeCorrectionTypes: true,

  includeCorrectionExplanations: true,

});

await Proofreader.create({

  expectedInputLanguages: ['en'],

  correctionExplanationLanguage: 'en',

  includeCorrectionTypes: true,

  includeCorrectionExplanations: true,

});

Thank you!

Cheers,

Tom

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[Bryan Dhaniel]

Hi Tom,

Here is the information you requested.

1.  **Output of `Proofreader.availability()`:**
    `'downloading'`

2.  **Output of `Proofreader.create()`:**
    The command did not produce any output or error in the console. It appears to be hanging or pending indefinitely.

await Proofreader.availability({
  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,
});

'downloading'

await Proofreader.create({
  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,
});

3.  **Output of `chrome://version`:**
    
hrome
140.0.7339.208 (Official Build) (64-bit) (cohort: Stable) 

Revision
c759967f1b8ca5857065acaa4f7b5cdb3a12df7b-refs/branch-heads/7339@{#2365}
OS
Windows 11 Version 24H2 (Build 26100.6725)
JavaScript
V8 14.0.365.10
User Agent
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Safari/537.36
Command Line
"C:\Program Files\Google\Chrome\Application\chrome.exe" --restart --flag-switches-begin --enable-features=AIPromptAPI:langs/%2A,AIPromptAPIMultimodalInput,AIProofreadingAPI,AISummarizationAPI:langs/%2A,AIWriterAPI:langs/%2A,OnDeviceModelPerformanceParams,ParallelDownloading --flag-switches-end
Executable Path
C:\Program Files\Google\Chrome\Application\chrome.exe
Profile Path
C:\Users\hp\AppData\Local\Google\Chrome\User Data\Profile 1
Command-line Variations
eyJkaXNhYmxlLWZlYXR1cmVzIjoiQU5HTEVQZXJDb250ZXh0QmxvYkNhY2hl...

Active Variations
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5076f4a6-f9a43703
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9cf6c713-ca7d8d80
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3c8f75a1-a6f840a5
a4406b35-1657e2d6
408da146-1657e2d6
1ac2b7d3-6c999558

Thank you!

[Thomas Steiner]

On Tue, Sep 30, 2025 at 1:05 PM Bryan Dhaniel <bryandh...@gmail.com> wrote:

Hi Tom,

Here is the information you requested.

1.  **Output of `Proofreader.availability()`:**
    `'downloading'`

This looks good.

 

2.  **Output of `Proofreader.create()`:**
    The command did not produce any output or error in the console. It appears to be hanging or pending indefinitely.

This is to be expected, as it will only resolve once the download has finished. 

Can you run one more test? The bold part is new and should show download progress. 

const proofreader = await Proofreader.create({

  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,

  monitor(m) {
    m.addEventListener("downloadprogress", e => {
      console.log(`Downloaded ${e.loaded * 100}%`);
    });
  }
});

 

Just to be sure, could I also ask you to check the same command in Chrome Canary? 

[Thomas Steiner]

Actually, posted a moment too soon, before advancing to my next email in my Inbox: apparently the `downloadprogress` events are currently broken, so you won't see progress other than 0 and then finally 1, but nothing in between. 

[Bryan Dhaniel]

Hi Tom,

Thank you for the guidance. I have completed the tests on both browsers as requested. The results are quite interesting.

1.  **Results from my current Chrome (Version 140.0.7339.208):**

    * On the first attempt, the command did not produce any output and seemed to hang, similar to the previous issue.
    * However, on the second attempt, it worked successfully! The console immediately showed the following output, and the command completed without hanging:
        Downloaded 0%
        Downloaded 100%

       const proofreader = await Proofreader.create({

  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,
  monitor(m) {
    m.addEventListener("downloadprogress", e => {
      console.log(`Downloaded ${e.loaded * 100}%`);
    });
  }
});

const proofreader = await Proofreader.create({
  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,
  monitor(m) {
    m.addEventListener("downloadprogress", e => {
      console.log(`Downloaded ${e.loaded * 100}%`);
    });
  }
});

VM246:8 Downloaded 0%
VM246:8 Downloaded 100%


2.  **Results from Chrome Canary (Version  142.0.7444.0 ):**

     * On the first attempt, the command did not produce any output and seemed to hang, similar to the normal chrome.
    * However, on the second attempt, it worked successfully! The console immediately showed the following output, and the command completed without hanging wth undefined:
        Downloaded 0%
        Downloaded 100%

        undefined

const proofreader = await Proofreader.create({

  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,
  monitor(m) {
    m.addEventListener("downloadprogress", e => {
      console.log(`Downloaded ${e.loaded * 100}%`);
    });
  }
});

VM247:9 Downloaded 0%
VM247:9 Downloaded 100%
undefined

I hope this detailed behavior provides the clues you need. Let me know if there's anything else I can test.

Thanks!

[Thomas Steiner]

Thanks for confirming that it worked. The 0 → 1 behavior is working as specified, even if the model is already downloaded. The bug I mentioned before was about the missing in-between progress updates that you would use to, for example, advance a `<progress>` bar. Glad we got the situation resolved for you!

Cheers,

Tom

[Bryan Dhaniel]

Hi Tom,

Thanks for the clarification on the download progress.

I have a follow-up question: even after the console shows the download is 100% complete, the proofreading function still doesn't work on my end. It seems to fail silently without any new errors.

Is this something you've seen before, or is there another test I can run to check if the model is initialized correctly after downloading?

Thanks!

[Thomas Steiner]

There is this short moment where the model is downloaded but needs to be extracted and the fine-tuning applied. This should not be observable much in practice, though. Can you run the code below and let me know?

const proofreader = await Proofreader.create({
  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,
  monitor(m) {
    m.addEventListener("downloadprogress", e => {
      console.log(`Downloaded ${e.loaded * 100}%`);
    });
  }
});

await proofreader.proofread('I am ful of typso');

It should look something like this:

[Bryan Dhaniel]

Hi Tom,

Thanks for the new test command. I have some great news!
**In Chrome Canary, the test was successful.** The output in the console looks exactly like the example you provided.

Does this mean the model has been successfully downloaded, initialized, and is now fully working in Canary?



For your information, in my normal Chrome, the same command still **[the output stuck on downloaded 100%]**.

Thank you so much for all your help!

[Thomas Steiner]

Yay, progress! At least in Canary we're good. For Stable, can you try quitting the browser completely and start fresh? If this doesn't help, try starting Chrome with a throw-away user data directory. This means you will need to download the model again in this test profile, but this way we can be sure it's not due to a corrupt profile or so.

[Yusuf Rawat]

1. https://vercel.com/blog/framework-defined-infrastructure

If you building for scale   or security 

Secure way to not reveal token , url , stripe uses it for payments  

1. Token can be concatenated yes if too long 

Token set expire 

Local , prod , date timing adjustment addressed 

I thought cookies banned in EU? Anyway if not this franework still applies , preloading , hotliading ,  attacks mentioned , https doesnt mean secure , rest  mentioned sync asyc or force option to avoid redownload or re problem mentioned 

In my opinion 

Pushing code passing via *client browsers* framework fits use case 

Dev , prod , local , idea applies and the code seperated browser 

Its all mentioned on first page 

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[Bryan Dhaniel]

I've done the tests. There is a clear difference in the API response between Chrome Stable (Test) and Chrome Canary.

1. On Chrome Stable (test):
The console log shows that the API is only returning `correctedInput` and is missing the `corrections` array entirely.
* Log snippet: `Raw proofread result: {correctedInput: 'I am full of typos.'}`

2. On Chrome Canary:
Everything works perfectly. The console log confirms the API is returning the complete object with both `correctedInput` and the `corrections` array.
* Log snippet: `Raw proofread result: {correctedInput: 'I am full of typos.', corrections: Array(2)}`

3. On Chrome Stable(original):
It is stuck on download, when I run this
await Proofreader.availability({

  expectedInputLanguages: ['en'],
  correctionExplanationLanguage: 'en',
  includeCorrectionTypes: true,
  includeCorrectionExplanations: true,

});

in test chrome = available
in original chrome = downloading

[Bryan Dhaniel]

Thank you for the clarification