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domfarolino merged 2 commits into from
Mar 5, 2026
Merged

Remove provideContext() and clearContext() #132

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fd8c5b8
Remove provideContext() and clearContext()
domfarolino Mar 5, 2026
d89d044
Update proposal.md
domfarolino Mar 5, 2026
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66 changes: 20 additions & 46 deletions docs/proposal.md
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Original file line number Diff line number Diff line change
Expand Up @@ -52,34 +52,9 @@ Handling tool calls in the main thread with the option of delegating to workers
## API

### modelContext
The `window.navigator.modelContext` interface is introduced for the site to declare functionality that can be used by an AI Agent. Access to these tools is arbitrated by the browser. The `modelContext` object has a `provideContext` method that's used to update the context (currently just tools) available to these agents. The method takes an object with a `tools` property which is a list of tool descriptors. The tool descriptors look as shown in this example below, which aligns with the Prompt API's [tool use](https://github.com/webmachinelearning/prompt-api#tool-use) specification, and other libraries like the MCP SDK:
The `window.navigator.modelContext` interface is introduced for the site to declare functionality that can be used by an AI Agent. Access to these tools is arbitrated by the browser.

```js
// Declare tool schema and implementation functions.
window.navigator.modelContext.provideContext({
tools: [
{
name: "add-todo",
description: "Add a new todo item to the list",
inputSchema: {
type: "object",
properties: {
text: { type: "string", description: "The text of the todo item" }
},
required: ["text"]
},
execute: ({ text }, agent) => {
// Add todo item and update UI.
return /* structured content response */
}
}
]
});
```

The `provideContext` method can be called multiple times. Subsequent calls clear any pre-existing tools and other context before registering the new ones. This is useful for single-page web apps that frequently change UI state and could benefit from presenting different tools depending on which state the UI is currently in. For a list of tools passed to `provideContext`, each tool name in the list is expected to be unique.

Alternatively, the `registerTool`/`unregisterTool` APIs can be used to add/remove tools from the registered set without resetting the state entirely.
The `modelContext`'s `registerTool()` and `unregisterTool()` methods are used to add and remove tools from the agent's context.

```js
window.navigator.modelContext.registerTool({
Expand All @@ -101,6 +76,7 @@ window.navigator.modelContext.registerTool({

window.navigator.modelContext.unregisterTool("add-todo");
```

### agent
The `agent` interface is introduced to represent an AI Agent using the functionality declared by the site through the `modelContext`. The lifetime of this interface is scoped to the execution of a tool. It is passed as a parameter when executing a tool's function. This interface provides the dependencies required by the site from the Agent.

Expand Down Expand Up @@ -246,30 +222,28 @@ function addStamp(stampName, stampDescription, stampYear, stampImageUrl) {
}
```

To let AI agents use this functionality, the author defines the available tools. The `agent` property on the `Window` is checked to ensure the browser supports WebMCP. If supported, the `provideContext()` method is called, passing in an array of tools with a single item, a definition for the new "Add Stamp" tool. The tool accepts as parameters the same set of fields that are present in the HTML form, since this tool and the form should be functionally equivalent.
To let AI agents use this functionality, the author defines the available tools. The `modelContext` property on the `Window` is checked to ensure the browser supports WebMCP. If supported, the `registerTool()` method is called with an object describing the new "Add Stamp" tool. The tool accepts as parameters the same set of fields that are present in the HTML form, since this tool and the form should be functionally equivalent.

```js
if ("modelContext" in window.navigator) {
window.navigator.modelContext.provideContext({
tools: [
{
name: "add-stamp",
description: "Add a new stamp to the collection",
inputSchema: {
type: "object",
properties: {
name: { type: "string", description: "The name of the stamp" },
description: { type: "string", description: "A brief description of the stamp" },
year: { type: "number", description: "The year the stamp was issued" },
imageUrl: { type: "string", description: "An optional image URL for the stamp" }
},
required: ["name", "description", "year"]
window.navigator.modelContext.registerTool({
{
name: "add-stamp",
description: "Add a new stamp to the collection",
inputSchema: {
type: "object",
properties: {
name: { type: "string", description: "The name of the stamp" },
description: { type: "string", description: "A brief description of the stamp" },
year: { type: "number", description: "The year the stamp was issued" },
imageUrl: { type: "string", description: "An optional image URL for the stamp" }
},
execute({ name, description, year, imageUrl }, agent) {
// TODO
}
required: ["name", "description", "year"]
},
execute({ name, description, year, imageUrl }, agent) {
// TODO
}
]
}
});
}
```
Expand Down
41 changes: 0 additions & 41 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,24 +136,12 @@ The {{ModelContext}} interface provides methods for web applications to register
<xmp class="idl">
[Exposed=Window, SecureContext]
interface ModelContext {
undefined provideContext(optional ModelContextOptions options = {});
undefined clearContext();
undefined registerTool(ModelContextTool tool);
undefined unregisterTool(DOMString name);
};
</xmp>

<dl class="domintro">
<dt><code><var ignore>navigator</var>.{{Navigator/modelContext}}.{{ModelContext/provideContext(options)}}</code></dt>
<dd>
<p>Registers the provided context (tools) with the browser. This method clears any pre-existing tools and other context before registering the new ones.
</dd>

<dt><code><var ignore>navigator</var>.{{Navigator/modelContext}}.{{ModelContext/clearContext()}}</code></dt>
<dd>
<p>Unregisters all context (tools) with the browser.
</dd>

<dt><code><var ignore>navigator</var>.{{Navigator/modelContext}}.{{ModelContext/registerTool(tool)}}</code></dt>
<dd>
<p>Registers a single tool without clearing the existing set of tools. The method throws an error, if a tool with the same name already exists, or if the {{ModelContextTool/inputSchema}} is invalid.
Expand All @@ -165,20 +153,6 @@ interface ModelContext {
</dd>
</dl>

<div algorithm>
The <dfn method for=ModelContext>provideContext(<var ignore>options</var>)</dfn> method steps are:

1. TODO: fill this out.

</div>

<div algorithm>
The <dfn method for=ModelContext>clearContext()</dfn> method steps are:

1. TODO: fill this out.

</div>


<div algorithm>
The <dfn method for=ModelContext>registerTool(<var ignore>tool</var>)</dfn> method steps are:
Expand All @@ -194,21 +168,6 @@ The <dfn method for=ModelContext>unregisterTool(<var ignore>name</var>)</dfn> me

</div>

<h4 id="model-context-options">ModelContextOptions Dictionary</h4>

<xmp class="idl">
dictionary ModelContextOptions {
sequence<ModelContextTool> tools = [];
};
</xmp>

<dl class="domintro">
<dt><code><var ignore>options</var>["{{ModelContextOptions/tools}}"]</code></dt>
<dd>
<p>A list of {{ModelContextOptions/tools}} to register with the browser. Each tool name in the list is expected to be unique.
</dd>
</dl>

<h4 id="model-context-tool">ModelContextTool Dictionary</h4>

The {{ModelContextTool}} dictionary describes a tool that can be invoked by [=agents=].
Expand Down