LGTM2. Seems like a metrics bug to me, I'd be happy to use actual tool invocation as the metric that matters here (that's where the burn-in risk would come from). Is there a public UseCounter for that already?
Rick On Wed, Oct 28, 2026 at 11:59 AM Mike Taylor <[email protected]> wrote: > LGTM1, given the "actual invocation" info below. Thanks. > On 10/28/26 2:55 p.m., 'Yashaswini Kumar' via blink-dev wrote: > > Hi blink-dev and API Owners, > > We would like to request an Origin Trial usage limit exception for the > WebMCP experiment to allow page load usage to exceed the 0.5% warning > threshold up to a maximum of 2.0%. > > ### Context > > WebMCP's Origin Trial registration usage has recently crossed the warning > threshold, currently sitting at approximately 0.51% of all Chrome page > loads. Under typical Origin Trial guidance, reaching 0.5% warrants either > asking partners to throttle usage or requesting an exception from API > owners before approaching the 1.0% trial limit. > > ### Justification & Burn-in Risk Assessment > > We believe extending the threshold to 2.0% carries negligible web burn-in > risk for the following reasons: > > 1. Token Registrations vs. Actual Invocation: > > The ~0.51% metric reflects pages where WebMCP tools are registered via > token. However, actual runtime invocation and execution of WebMCP tools by > AI agents is orders of magnitude lower than the page registration rate. > Site users do not actively execute tool calls on every visit. > > 2. Plateaued Growth: > > Partner registrations have largely stabilized and plateaued over the > past several months, indicating steady experimentation rather than runaway > exponential growth across the broader web. > > 3. Continued Operational Monitoring: > > The WebMCP team actively monitors partner usage and retains tight > operational controls, ensuring we can intervene well before usage > approaches 2.0%. > > ### Request > > We request 3 LGTMs from the Blink API Owners to grant an exception > allowing WebMCP Origin Trial usage up to 2.0% of Chrome page loads. > > Thanks, > > Yash on behalf of the Chrome WebMCP team > > > On Tuesday, September 29, 2026 at 2:47:43 PM UTC-4 [email protected] > wrote: > >> Hey Alex, yeah, we’re hoping to move to I2S within the extension window. >> >> So far we’ve learned a lot: >> >> The imperative API is a lot more popular than the declarative one, so >> we're investing more into it in response to user needs. >> >> 1. >> >> We received excellent feedback from Mozilla >> <https://github.com/webmachinelearning/webmcp/issues/236> about API >> changes we can make to benefit non-AI use cases, as a generic cross-realm >> function-calling primitive. >> 2. >> >> We've heard from partners with tools whose entrypoint is on one page, >> while the result is on another (after a navigation). So we're prototyping >> a >> continuation API >> >> <https://github.com/webmachinelearning/webmcp/blob/cont-explainer/continuations-explainer.md> >> that we'd like to get into the hands of developers. >> 3. >> >> We and popular frameworks anticipate gaps between async tool >> registration and when an agent collects a "snapshot" of a page's tools >> (driven by its page loading heuristics). So we're prototyping a tool >> stability API >> <https://github.com/webmachinelearning/webmcp/issues/328> to let >> developers inform agent heuristics when an appropriate observation time >> might be. We're discussing this with major model vendors and want to >> understand how this impacts performance in the real world. >> 4. >> >> Some developers expressed a desire to pass user activation from an >> in-page agent (on a top-level document), into the page hosting a a >> tool. We're tracking this in >> https://github.com/webmachinelearning/webmcp/issues/62, but before >> pursuing a proposal like capability delegation >> <https://github.com/WICG/capability-delegation>, we'd like more >> experimentation to help us understand how much this comes up in practice. >> 5. >> >> We're exploring what it might look like to enforce size/character >> limits on tools >> <https://github.com/webmachinelearning/webmcp/issues/219>, and we'd >> benefit from more time to experiment after discussing what a reasonable >> limit might look like with other browsers and major model vendors. >> >> >> Those are a few things we've learned so far, and in particular, how we'd >> benefit from an extended experiment to understand how our proposed changes >> play with real-world sites and agents. >> On Monday, September 28, 2026 at 7:57:08 PM UTC-4 Alex Russell wrote: >> >>> LGTM1 conditional on some summary of developer feedback from the first >>> OT. What did we learn? Are we making API shape changes in response? And why >>> aren't we moving to I2S yet (or is that anticipated in this extension >>> window)? >>> >>> Best, >>> >>> Alex >>> >>> On Monday, September 28, 2026 at 4:13:33 PM UTC-7 Chromestatus wrote: >>> >>>> *Contact emails* >>>> [email protected], [email protected], [email protected], >>>> [email protected], [email protected], [email protected], >>>> [email protected] >>>> >>>> *Explainer* >>>> https://github.com/webmachinelearning/webmcp >>>> >>>> *Specification* >>>> https://webmachinelearning.github.io/webmcp >>>> >>>> *Design docs* >>>> >>>> >>>> https://docs.google.com/document/d/1ZaQvuj4YnUnoqOfEhbfgFynpDRKk2zZZHavTNJ151gM/edit?tab=t.0#heading=h.ggi78l861caa >>>> >>>> https://docs.google.com/document/d/1ycdzuXA-VE8lRDFSArh0Um3PChHV0Hq6Om1MSMG8qPE/edit?tab=t.0#heading=h.edohi3f5z12h >>>> >>>> *Summary* >>>> WebMCP is a proposal for a web API that enables web pages to provide >>>> agent-specific paths in their UI. With WebMCP, agent-service interaction >>>> takes place via app-controlled UI, providing a shared context available to >>>> app, agent, and user. >>>> >>>> *Blink component* >>>> Blink>Agentic Platform>WebMCP >>>> <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3EAgentic%20Platform%3EWebMCP%22> >>>> >>>> *Web Feature ID* >>>> document-modelcontext >>>> <https://webstatus.dev/features/document-modelcontext> >>>> >>>> *Search tags* >>>> WebMCP <http:///features#tags:WebMCP> >>>> >>>> *TAG review* >>>> Spec is being incubated. We will request TAG review before shipping. >>>> >>>> *TAG review status* >>>> Pending >>>> >>>> *Origin Trial Name* >>>> WebMCP >>>> >>>> *Goals for experimentation* >>>> For the experiment we are focused on understanding the API ergonomics >>>> for agentic workflows across various verticals such as web commerce and >>>> productivity. We expect the site owners to implement WebMCP tools in their >>>> sites to automate high-value workflows for them and will seek feedback on >>>> the functionality of WebMCP. We also plan to gather metrics for tool usage >>>> and latency, and assess opportunities for improvements. >>>> >>>> *Chromium Trial Name* >>>> WebMCP >>>> >>>> *Origin Trial documentation link* >>>> >>>> https://docs.google.com/document/d/1ZaQvuj4YnUnoqOfEhbfgFynpDRKk2zZZHavTNJ151gM/edit?tab=t.0#heading=h.ggi78l861caa >>>> >>>> *WebFeature UseCounter name* >>>> kModelContextRegisterTool >>>> >>>> *Risks* >>>> >>>> >>>> *Interoperability and Compatibility* >>>> Given this is a new space and new API - there's no compatibility risk. >>>> Usual risk related to other browser vendors not adopting the API apply. >>>> This API is meant to augment capabilities provided by browser add-ons and >>>> so non-adoption in other engines would have limited user-impact and thus we >>>> consider the risk to be low. >>>> >>>> *Gecko*: No signal >>>> >>>> *WebKit*: No signal >>>> >>>> *Web developers*: No signals Web Framework developers: Have shown a >>>> great deal of interest during the developer trial, as evidenced here: >>>> https://www.star-history.com/?repos=webmachinelearning%2Fwebmcp&type=date&legend=bottom-right >>>> Chrome web store features about 9 different extensions with WebMCP on their >>>> title and 4* or more ratings. >>>> https://chromewebstore.google.com/search/WebMCP?minimalRating=4 >>>> >>>> *Other signals*: >>>> >>>> *Ergonomics* >>>> There is a risk that site authors that wish to incorporate WebMCP tools >>>> into their sites will need to duplicate functionality that currently exists >>>> to drive the user interface. We're hoping that most imperative WebMCP tools >>>> are just thin wrappers around existing code that drives actions on the >>>> site, but we are working with framework developers like React to ensure >>>> that WebMCP tools can be added without rearchitecting the site logic. We >>>> are also offering a declarative version that requires only adding >>>> attributes to existing form elements, which is much lighter weight to >>>> deploy and does not require any refactoring of existing site functionality. >>>> >>>> *Activation* >>>> There are no activation requirements to register WebMCP tools. To >>>> execute WebMCP tools does require an agent, either provided by the browser >>>> or site author, to formulate and orchestrate tool calls. There are several >>>> Chrome extensions already available that allow cloud-LLM-based agents to >>>> discover and call WebMCP tools. It is also possible to use the Prompt API >>>> to call WebMCP tools using on-device models. >>>> >>>> *Security* >>>> Sites may consume and expose sensitive information when their WebMCP >>>> tools are called by agents. Agents should implement safeguards to ensure >>>> that sensitive information is passed to sites and between origins only >>>> under the consent of the user that is supervising them. LLM-based agents >>>> are susceptible to attacks such as indirect prompt injection, which can >>>> cause an exploited agent to exfiltrate sensitive information in its context >>>> to an attacker. Agents should implement safeguards against prompt injection >>>> and related attacks. >>>> >>>> *WebView application risks* >>>> >>>> Does this intent deprecate or change behavior of existing APIs, such >>>> that it has potentially high risk for Android WebView-based applications? >>>> *No information provided* >>>> >>>> >>>> *Reason this experiment is being extended* >>>> OT feedback has suggested improvements to the API, which we are >>>> implementing. The OT extension would enable us to get data on those >>>> improvements as well as to continue getting data on the rest of the >>>> feature. >>>> >>>> *Ongoing technical constraints* >>>> No technical constraints for the experiments. >>>> >>>> *Debuggability* >>>> Explicit debugging support through a new WebMCP Chrome DevTools >>>> Protocol domain. The domain supports listing registered tools, invoking >>>> tools, and logging all calls by agents. Registration issues for declarative >>>> tools (e.g., missing names or descriptions) are reported through the Audits >>>> domain. >>>> >>>> *Will this feature be supported on all six Blink platforms (Windows, >>>> Mac, Linux, ChromeOS, Android, and Android WebView)?* >>>> Yes >>>> >>>> *Is this feature fully tested by web-platform-tests >>>> <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?* >>>> No >>>> The IDL and basic usage is tested via WPTs. Since the API provides the >>>> user agent with the ability to call certain tools, we might need to extend >>>> the WPT harness to support this. >>>> >>>> *DevTrial instructions* >>>> >>>> https://docs.google.com/document/d/1rtU1fRPS0bMqd9abMG_hc6K9OAI6soUy3Kh00toAgyk/edit?tab=t.0 >>>> >>>> *Flag name on about://flags* >>>> Experimental Web Platform features >>>> >>>> *Finch feature name* >>>> WebMCP >>>> >>>> *Requires code in //chrome?* >>>> True >>>> >>>> *Tracking bug* >>>> https://crbug.com/445637567 >>>> >>>> *Launch bug* >>>> https://launch.corp.google.com/launch/4460611 >>>> >>>> *Estimated milestones* >>>> Origin trial desktop first 149 >>>> Origin trial desktop last 156 >>>> Origin trial extension 1 end milestone 162 >>>> DevTrial on desktop 146 >>>> Origin trial Android first 149 >>>> Origin trial Android last 156 >>>> DevTrial on Android 146 >>>> Origin trial WebView first 149 >>>> Origin trial WebView last 156 >>>> >>>> *Link to entry on the Chrome Platform Status* >>>> https://chromestatus.com/feature/5117755740913664?gate=5151396285513728 >>>> >>>> *Links to previous Intent discussions* >>>> Intent to Prototype: >>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CANMmsAtRdyRw1WtO5va0K%3D_adYH-FRh01xvw5%2BosSd_DAq%3D%3DUQ%40mail.gmail.com >>>> Ready for Trial: >>>> https://groups.google.com/a/chromium.org/g/blink-dev/c/bhhOmTGzD5Y/m/PGdM8lF6AQAJ >>>> Intent to Experiment: >>>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6a076b26.050a0220.3377b4.05fa.GAE%40google.com >>>> >>>> >>>> This intent message was generated by Chrome Platform Status >>>> <https://chromestatus.com>. >>>> >>> -- > You received this message because you are subscribed to the Google Groups > "blink-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/f5a0e368-dc5c-40ae-b1f6-ffb3808262c7n%40chromium.org > <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/f5a0e368-dc5c-40ae-b1f6-ffb3808262c7n%40chromium.org?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "blink-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/d22099ab-5743-43ca-9a4e-6906cd926ec1%40chromium.org > <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/d22099ab-5743-43ca-9a4e-6906cd926ec1%40chromium.org?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. 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