MCP App object

An McpApp bundles a user interface with the tools it calls. It knows how to render itself as the self-contained HTML page an MCP host shows (the app's ui:// resource), how to describe its tools to a client, and how to run them. Create one with mcp_app() or as_mcp_app() rather than calling McpApp$new() directly; the arguments are the same.

Most code only needs $call_tool() (run a tool and get its R value back, as in tests) and $html_resource() (the page a host renders).

See also

Other apps: as_mcp_app(), bindMcp(), mcp_app(), mcp_tool_module()

Public fields

name

App name; the UI resource is ui://<name>, with any characters a URI can't carry percent-encoded.

version

App version string.

title

Human-readable title, or NULL.

description

What the app is for, or NULL.

Methods

Public methods

• McpApp$new()

• McpApp$html_resource()

• McpApp$resource_uri()

• McpApp$resource_meta()

• McpApp$resources()

• McpApp$read_resource()

• McpApp$has_resource()

• McpApp$tools()

• McpApp$tool_definitions()

• McpApp$call_tool()

• McpApp$run_tool()

• McpApp$has_tool()

• McpApp$interaction_defaults()

• McpApp$runtime()

• McpApp$close()

• McpApp$output_types()

• McpApp$print()

• McpApp$clone()

---

McpApp$new()

Create an app. See mcp_app() for the arguments.

Usage

McpApp$new(
  ui,
  tools = list(),
  name = "shinymcp-app",
  version = "0.1.0",
  title = NULL,
  description = NULL,
  theme = NULL,
  csp = NULL,
  permissions = NULL,
  prefers_border = NULL,
  domain = NULL,
  tool_visibility = NULL,
  tool_outputs = NULL,
  trigger = NULL,
  debounce_ms = NULL,
  resources = NULL,
  host_styles = TRUE,
  model_context = TRUE,
  images = TRUE,
  www = NULL,
  runtime = NULL
)

Arguments

ui, tools, name, version, title, description, theme, csp, permissions, prefers_border, domain, tool_visibility, tool_outputs, trigger, debounce_ms, resources, host_styles, model_context, images, www

See mcp_app().

runtime

Internal: the live Shiny runtime for apps created by as_mcp_app() from a Shiny app.

---

McpApp$html_resource()

The HTML page an MCP host renders for this app. Dependencies (Bootstrap, bslib components, htmlwidgets) are inlined so the page works under a host's default Content Security Policy.

Usage

McpApp$html_resource(config = NULL)

Arguments

config

Named list merged into the bridge configuration. Hosts use it to pass their own settings; apps rarely need it.

---

McpApp$resource_uri()

The app's ui:// resource URI.

Usage

McpApp$resource_uri()

---

McpApp$resource_meta()

The _meta published with the app's ui:// resource (CSP, permissions, border preference), or NULL.

Usage

McpApp$resource_meta()

---

McpApp$resources()

Resource records for resources/list: the app's UI and any extra resources.

Usage

McpApp$resources()

---

McpApp$read_resource()

Read one of the app's resources.

Usage

McpApp$read_resource(uri)

Arguments

uri

Resource URI.

Returns

A resources/read contents entry (uri, mimeType, text, optional _meta).

---

McpApp$has_resource()

Does the app serve this resource URI?

Usage

McpApp$has_resource(uri)

Arguments

uri

Resource URI.

---

McpApp$tools()

The app's tools, normalized.

Usage

McpApp$tools(audience = NULL)

Arguments

audience

NULL for all tools, or "model" / "app" for the tools that audience may call.

---

McpApp$tool_definitions()

Tool definitions for an MCP tools/list response.

Usage

McpApp$tool_definitions(include_ui_meta = TRUE, include_app_only = TRUE)

Arguments

include_ui_meta

Include the nested _meta.ui block. FALSE for clients that did not declare MCP Apps support.

include_app_only

Include tools only the app's UI can call.

---

McpApp$call_tool()

Run a tool and return its R value, as the tool function returned it. Useful in tests.

Usage

McpApp$call_tool(name, arguments = list(), context = list())

Arguments

name

Tool name.

arguments

Named list of arguments, as a client would send them. A vector of one value is one value; write an array of one as list(x).

context

Request context; see mcp_request().

---

McpApp$run_tool()

Run a tool and return an MCP tools/call result.

Usage

McpApp$run_tool(name, arguments = list(), context = list(), raw = FALSE)

Arguments

name

Tool name.

arguments

Named list of arguments, as a client would send them. A vector of one value is one value; write an array of one as list(x).

context

Request context. caller = "app" marks calls from the app's own UI, and images = FALSE asks for a result without image blocks for the model.

raw

If TRUE, return a list with the result and the raw value the tool function returned (NULL if it failed).

---

McpApp$has_tool()

Does the app have a tool with this name?

Usage

McpApp$has_tool(name)

Arguments

name

Tool name.

---

McpApp$interaction_defaults()

The app's declared interaction defaults (trigger, debounce_ms), each possibly NULL.

Usage

McpApp$interaction_defaults()

---

McpApp$runtime()

The live Shiny runtime behind an app made from a Shiny app, or NULL.

Usage

McpApp$runtime()

---

McpApp$close()

Close the app's open views and stop the Shiny app behind it, if any, running its onStop hook. serve() and mcp_endpoint() call this when they stop.

Usage

McpApp$close()

---

McpApp$output_types()

Output ids and types found in the UI.

Usage

McpApp$output_types()

---

McpApp$print()

Print a summary.

Usage

McpApp$print(...)

Arguments

...

Ignored.

---

McpApp$clone()

The objects of this class are cloneable with this method.

Usage

McpApp$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.