preview_app() serves the app over MCP on a local port and opens a page
that hosts it the way a chat client does: the app runs in a sandboxed
iframe under the same Content Security Policy a client would apply, and
every message goes through the app's real MCP endpoint. Alongside the app
the page shows what the model would see (the text and structured content
of each tool result), the context the app publishes for the model, and a
log of the protocol messages.
When the page opens it calls the app's first tool (or tool) with
arguments, as a model would, and shows the app with the result. Use
the arguments box on the page to call it again with other values.
Usage
preview_app(
app,
arguments = NULL,
tool = NULL,
port = NULL,
launch = interactive()
)Arguments
- app
An McpApp, a list of apps, a Shiny app, or a path to one.
- arguments
Named list of arguments for the first call, as a client would send them. A vector of one value is one value; write an array of one as
list(x).- tool
Name of the tool to call first. Defaults to the first tool the model can call.
- port
Port to listen on.
NULLpicks a free one.- launch
Whether to open the page in a browser.
Value
Invisibly, a list with the preview's url and a stop()
function.
See also
Other serving:
mcp_endpoint(),
serve(),
shinymcp-options
Examples
if (FALSE) { # \dontrun{
preview <- preview_app(app, arguments = list(species = "Gentoo"))
preview$stop()
} # }