> ## Documentation Index > Fetch the complete documentation index at: https://docs.widgentic.dev/llms.txt > Use this file to discover all available pages before exploring further. # Host matrix > How each MCP host connects to widgentic, what it shows inline, and which action kinds work there. Same server, different hosts. The rows below are generic facts confirmed by probing the hosts; anything not confirmed says so. Registration snippets are in [Connect a host](/get-started/connect-a-host). | Host | How to connect | Inline widgets | Prompt actions (composer prefill) | http actions (needs `serverTools`) | Notes | | -------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------- | ------------------------------------------------------------ | ------------------------------------- | ------------------------------------------------------------------------------- | | claude.ai | Custom connector (Settings, Connectors, Add custom connector). Connectors accept a URL only, so a per-principal key travels as a query parameter: `https://mcp.widgentic.dev/mcp?key=` | Yes: mounts the MCP Apps template inline | Yes: `ui/message` prefills the composer and the person sends | Yes: proxies the frame's `tools/call` | Mounts a fresh iframe per render; advertises `message` but honours `ui/message` | | Claude Desktop | Custom connector as above, or stdio through `claude_desktop_config.json` with absolute paths | Yes: Apps-capable versions mount the page in chat | Not probed | Not probed | Versions without Apps support receive the text result | | VS Code Copilot Chat | `.vscode/mcp.json` with `"type": "http"`, the server URL and an `x-api-key` header | Yes: verified for all four built-in kinds plus a custom template widget | Yes: prefills the composer | Yes: proxies `tools/call` | Live host re-theming flows into the `--wg-*` tokens | | Claude Code | `claude mcp add widgentic -- npx tsx /path/to/examples/mcp-server/main.ts` (stdio) | No: tool results are text; no UI mounting by design | Not applicable, no frame | Not applicable, no frame | Ask for `format: "page"` and open the document in a browser | | MCP Apps basic-host | The official reference host pointed at a Streamable HTTP server built with `createWidgenticServer()` | Yes: the reference implementation | `ui/message` accepted | Yes: proxies `tools/call` | The cheapest place to probe the frame before a production host | | MCP Inspector | `npx @modelcontextprotocol/inspector npx tsx examples/mcp-server/main.ts` | Not part of our verification | Not applicable | Not applicable | Tool listing and raw tool results without any chat host | ## Facts that hold across Apps hosts * All three Apps hosts we probed — basic-host, claude.ai and VS Code Copilot Chat — honour `ui/message`, but only claude.ai advertises it. The frame therefore never gates prompt actions on the advertised flag; a host that answers with a JSON-RPC error gets an inline alert inside the frame while the widget stays intact. * `hostCapabilities.serverTools` in the initialize result is the reliable gate for http actions. Without it the frame renders http descriptors disabled with an explanatory `title`, and prompt actions stay enabled. All three probed hosts advertise it and proxy the frame's `tools/call` to the server. * App-side `tools/list` is unsupported everywhere (`-32601`), so the frame never enumerates tools; it calls `execute_action` by name. * Hosts cache `ui://` resources per conversation. After a server change, retest the template in a fresh chat. * Partial tool input (`tool-input-partial`) is size-gated by the host, so do not count on the streaming preview appearing for every payload; the tool result is always authoritative. * The sandbox CSP blocks external images. The server inlines them as `data:` URIs on iframe surfaces; see [Inline rendering](/how-it-works/inline-rendering). * claude.ai mounts a fresh iframe per render, so each render is a new widget instance; a `load` binding fires once per instance. ## Connecting to the hosted server The hosted server answers at `https://mcp.widgentic.dev/mcp`. Hosts that send headers (VS Code Copilot Chat) pass the key as `x-api-key`; hosts that accept only a URL (claude.ai and Claude Desktop connectors) take it as `?key=`. A request without a resolvable key still works over the built-in catalog, as described in [Per-principal catalogs](/how-it-works/per-principal-catalogs). Registration is never an MCP tool. Whatever host you connect, saving a widget happens in the authenticated app; the key only reads. See the [Trust model](/how-it-works/trust-model). ## Hosts without Apps support Any client that does not advertise the Apps capability receives the default result — the HTML fragment text block plus the widgentic payload block — with the template unmounted. Hosts that understand the `application/vnd.widgentic+json` block can mount it natively with `@widgentic/core`; see [Render in your host](/develop/render-in-your-host). Everyone else reads the HTML, or asks for `format: "page"`.