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How to Enable Chrome Built-in AI APIs for Grammar + Tone Fixing

Seeing the error "Built-in AI API is unavailable"? Follow this quick setup guide.

May 17, 2026 • 6 min read

Quick setup checklist

  • Open the Chrome flags page.
  • Enable both required feature flags.
  • Relaunch Chrome and retry the tool.
chrome://flags

If your Grammar + Tone Fixer shows Built-in AI API is unavailable, Chrome likely needs experimental flags enabled for this API path.

Step 1: Open flags page

Paste the URL below into Chrome address bar:

chrome://flags

Step 2: Enable required flags

Enable each flag below, one by one:

#prompt-api-for-gemini-nano
#optimization-guide-on-device-model

Step 3: Relaunch Chrome

Click the Relaunch button in Chrome after enabling both flags, then reopen the tool page.

Why this happens

Depending on Chrome version and rollout channel, Built-in AI capabilities may still require feature flags to be turned on manually.

Tips for better grammar + tone results

  • Use one focused paragraph per run for cleaner output.
  • Pick a target tone first (professional, friendly, concise, confident).
  • Review names, product terms, and numbers before sending.

Ready to use it? Open the Grammar + Tone Fixer.