MCP Resources — URIs, MIME Types & Reading

What Are MCP Resources?

Resources are data that an MCP server exposes for reading. Each resource is identified by a URI and has a MIME type. Unlike tools (which execute actions), resources represent data that can be fetched — files, structured data, or (in MCP Apps) interactive HTML UIs.

Discovery (`resources/list`)

The host calls resources/list to discover available resources. Each resource declares:

Field	Description
`uri`	Unique identifier (e.g., `"ui://weather/view.html"`)
`name`	Human-readable name
`description`	What the resource contains
`mimeType`	Content type (e.g., `"text/html"`, `"application/json"`)

{
  "uri": "ui://weather/view.html",
  "name": "Weather View",
  "description": "Interactive weather display",
  "mimeType": "text/html;profile=mcp-app"
}

URIs

Resources are identified by URIs. Servers can use any URI scheme. MCP Apps uses the ui:// scheme to identify UI resources that should be rendered in iframes.

MIME Types

Each resource declares its content type via mimeType. MCP Apps uses the MIME type text/html;profile=mcp-app (exported as RESOURCE_MIME_TYPE) to identify HTML resources that hosts should render as interactive Views.

Reading (`resources/read`)

The host calls resources/read with a resource URI to fetch its contents. The server returns an array of content items.

// Request
{ "method": "resources/read", "params": { "uri": "ui://weather/view.html" } }

// Response
{
  "contents": [{
    "uri": "ui://weather/view.html",
    "mimeType": "text/html;profile=mcp-app",
    "text": "<!DOCTYPE html>..."
  }]
}

In MCP Apps

MCP Apps extends resources with _meta.ui metadata on content items. This lets servers declare security policies (CSP), iframe permissions, rendering preferences, and stable sandbox origins for their UIs.

{
  "uri": "ui://weather/view.html",
  "mimeType": "text/html;profile=mcp-app",
  "text": "<!DOCTYPE html>...",
  "_meta": {
    "ui": {
      "csp": { "connectDomains": ["https://api.example.com"] },
      "permissions": { "geolocation": {} }
    }
  }
}

registerAppResource

Resource _meta

CSP, permissions, domain, and rendering metadata.

Overview

App

MCP

React

Server

Styling

Types

MCP Resources — URIs, MIME Types & Reading

What Are MCP Resources?

Discovery (`resources/list`)

URIs

MIME Types

Reading (`resources/read`)

In MCP Apps

registerAppResource

Resource _meta

​What Are MCP Resources?

​Discovery (resources/list)

​URIs

​MIME Types

​Reading (resources/read)

​In MCP Apps

registerAppResource

Resource _meta

What Are MCP Resources?

Discovery (`resources/list`)

URIs

MIME Types

Reading (`resources/read`)

In MCP Apps