Browser support
Web AI support lands engine by engine, and it is desktop-only for now: mobile browsers, including Chrome and Edge on iOS and Android, don’t expose these APIs yet. Where it isn’t there yet, every package is a feature-detected no-op so your code doesn’t crash; render whatever fallback UI you want.
| Package | Chrome | Edge | Safari | Firefox |
|---|---|---|---|---|
@web-ai-sdk/prompt | 148+ · stable | 138+ · Canary/Dev · flag | no-op fallback | no-op fallback |
@web-ai-sdk/summarizer | 138+ · stable | 138+ · stable | no-op fallback | no-op fallback |
@web-ai-sdk/translator | 138+ · stable | 148+ · stable | no-op fallback | no-op fallback |
@web-ai-sdk/detector | 138+ · stable | 148+ · stable | no-op fallback | no-op fallback |
@web-ai-sdk/writer | 137+ · OT · flag | 138+ · Canary/Dev · flag | no-op fallback | no-op fallback |
@web-ai-sdk/rewriter | 137+ · OT · flag | 138+ · Canary/Dev · flag | no-op fallback | no-op fallback |
@web-ai-sdk/proofreader | 141+ · OT · flag | 142+ · Canary/Dev · flag | no-op fallback | no-op fallback |
@web-ai-sdk/webmcp | 146+ · flag · OT 149+ | 147+ · flag | no-op fallback | no-op fallback |
Versions reflect when the underlying platform API became available. Wrapper exports stay stable across all browsers. stable = on by default, no flag; Canary/Dev = preview channel that still needs the matching edge://flags toggle enabled; flag = ships in the normal channel but stays behind a chrome://flags / edge://flags toggle; OT = origin trial. Per-API sources are linked under Edge specifics and in References below.
The Writing Assistance APIs (Writer, Rewriter) and the Proofreader API are still experimental: developer/origin trials in Chrome and developer previews in Edge Canary/Dev. Like the other Gemini Nano / Phi-4-mini APIs, they are desktop-only (no Android, iOS, or non-Chromebook-Plus ChromeOS) and are not available in Web Workers — top-level windows and same-origin iframes only (cross-origin iframes require a Permissions-Policy allow delegation).
Edge specifics
Section titled “Edge specifics”Summarizer (enabled by default since Edge 138, per the Edge Writing Assistance APIs docs), Translator (Edge 148+, per the Edge Translator API docs), and Language Detector (Edge 148+, per the Edge Language Detector API docs) all ship in Edge stable with no flag. The Prompt API is still a developer preview in Edge Canary/Dev 138+, the Writer and Rewriter APIs in Edge Canary/Dev 138+, and the Proofreader API in Edge Canary/Dev 142+, each behind its own ”… API for Phi mini” flag. WebMCP landed in Edge 147 behind a flag.
Prompt, Summarizer, Writer, Rewriter, and Proofreader all route through Phi-4-mini with a stricter safety pipeline than Chrome’s Gemini Nano; Translator and Language Detector run dedicated on-device models.
- macOS quirk: on macOS, the on-device model frequently refuses output for Prompt and Summarizer — summarizer returns “low quality output blocked”, prompt may emit C0 control-character placeholders. The library handles both (strips C0/C1, normalizes streaming shape, wraps refusals in typed errors), but the model itself is the bottleneck on that platform. Windows doesn’t reproduce this.
- Flags on
edge://flags/: “Prompt API for Phi mini”, “Writer API for Phi mini”, “Rewriter API for Phi mini”, “Proofreader API for Phi mini”. Summarizer (Edge 138+), Translator (Edge 148+), and Language Detector (Edge 148+) ship on by default with no flag. - Hardware check:
edge://on-device-internalsmust show a “High” device performance class.
WebMCP on Edge isn’t yet covered by an official Microsoft developer-docs page; the version above reflects empirical Canary/Dev testing.
References: Microsoft Learn: Prompt · Writing Assistance · Proofreader · Translator · Language Detector.
Enabling on Chrome
Section titled “Enabling on Chrome”| Surface | Flag |
|---|---|
| WebMCP | chrome://flags/#enable-webmcp-testing (Chrome 146+); origin trial opens in Chrome 149 |
| Prompt API | Stable in Chrome 148+ (no flag); Chrome 138–147 needs chrome://flags/#prompt-api-for-gemini-nano |
| Summarizer, Translator, Detector | Stable in Chrome 138+ |
| Writer & Rewriter | chrome://flags/#writer-api-for-gemini-nano (joint trial; Chrome 137–148). Rewriter has no separate flag — it shares the Writer toggle |
| Proofreader | chrome://flags/#proofreader-api-for-gemini-nano (Chrome 141–145) |
The Writing Assistance and Proofreader flags also require chrome://flags/#optimization-guide-on-device-model enabled. After enabling a flag, restart Chrome and wait for the on-device model to download (chrome://on-device-internals).