Originally published at https://dev.to/anhmtk/native-webmcp-on-a-live-mcp-registry-4a8
This is the same integration, written here so the source stays on dev.to. https://agentshare.dev/registry registers one read-only tool, search_listings, on document.modelContext when that API exists in the open Chrome tab. An agent that never opens a browser still calls remote MCP at https://agentshare.dev/mcp.
Two ways to read the same registry
| Remote MCP | Native WebMCP |
|---|
| Where | https://agentshare.dev/mcp | https://agentshare.dev/registry, tab open |
| Call style | Streamable HTTP. API key or x402 | document.modelContext in Chrome |
| Lifetime | The server stays up | Ends when the tab closes |
| Payload | The MCP tool list, including paid Objective Trust | search_listings only. Public fields. At most 5 matches |
Remote MCP is for an agent that is not on the page. WebMCP is for an agent that already has the registry tab open in Chrome and can call getTools / executeTool.
What the page registers
The script is https://agentshare.dev/static/js/webmcp-registry.js. It returns immediately when document.modelContext.registerTool is missing. It does not install a polyfill.
The tool is read-only. readOnlyHint is true. untrustedContentHint is true because listing descriptions are written by the people who submitted them.
execute calls GET /api/v1/registry/entries on the same origin. limit is clamped to 1–5. sort is new or popular. Featured rows still sort first. Featured does not change health_status and is not a trust rank.
The page aborts the registration on pagehide.
The envelope models can quote
Every successful call returns schema set to agentshare.catalog.v1.
{
"schema": "agentshare.catalog.v1",
"catalog_as_of": "2026-10-30T03:15:00Z",
"listed": 147,
"sort": "featured_then_newest",
"sort_note": "Featured listings sort first. Featured does not change health_status and is not a trust rank.",
"returned": 1,
"matches": [
{
"id": 0,
"name": "Example listing",
"description_excerpt": "Short public description, clipped to 160 characters.",
"health_status": "responding",
"reviewed": true,
"category": "agent_tools",
"opens": 0,
"featured": false,
"mcp_url": "https://example.com/mcp"
}
],
"next": "For a rank that ignores featured and sponsored, call Objective Trust at https://agentshare.dev/mcp/objective-trust"
}
catalog_as_of and listed in that sample are the shape, not a frozen snapshot. On a live call, catalog_as_of is generated_at from that entries response: the server clock when the catalog was built for the tool call. It is not Date.now() in the browser. listed is total_listed on the same response.
reviewed: true means the row status is verified. health_status is the stored probe label, such as responding, needs_sign_in, unreachable, not_remote, or unknown. description_excerpt is clipped. The Objective Trust score is not in this object. The next field points at the paid ranker, which ignores featured and sponsored.
A model that quotes this payload can cite three stable facts: the schema name agentshare.catalog.v1, the page https://agentshare.dev/registry, and a server timestamp for that response.
Checking the open tab
AgentShare Agent Readiness 0.6.0 reads native document.modelContext on the active tab when you open the popup. It lists each tool name and whether the tool is read-only, consequential, or marked untrusted content.
The score gains 4 points when the tab has at least one native tool. No native API means no point change. A missing untrustedContentHint is a warning, not a penalty. A polyfill that only sets document.modelContext inside the page is invisible to the extension. The reference score for agentshare.dev stays 92.
The scan stays in the browser. Tool names are not uploaded.
Where to look
