Resources in Tools

In the previous exercise, you learned how to expose structured data (like journal entries and tags) as resources using the Model Context Protocol (MCP). You registered resources, made them discoverable, and enabled clients to list and read them by URI.
But the data our tools return involves those resources. What if you want a tool to return a resource, or a reference to one, as part of its response? This is where MCP's support for embedding and linking resources in tool responses comes in.
By embedding or linking resources in your tool responses, you enable clients and LLMs to:
  • Access rich, structured context directly from tool outputs
  • Subscribe to updates or fetch more details on demand
  • Build workflows that combine actions (tools) and context (resources)
This unlocks powerful new user experiences, like letting a user create a journal entry and immediately get a reference to it, or listing all tags as clickable resource links.

Embedded Resources

Sometimes, you want your tool to return the full resource data. MCP supports this with the type: 'resource' content type in tool responses. This embeds the resource (including its URI, mimeType, and data) directly in the response.
{
	"type": "resource",
	"resource": {
		"uri": "gym://equipment/beam-001",
		"mimeType": "application/json",
		"text": "{\"name\":\"Balance Beam\",\"category\":\"Apparatus\",\"length\":5.0,\"unit\":\"meters\"}"
	}
}
This is useful when the resource is small or when you want the client/LLM to have all the details immediately.

Linked Resources

Other times, you want to reference a resource without including all its data. MCP supports this with the type: 'resource_link' content type. This provides a URI and metadata, letting the client/LLM fetch the resource if needed.
{
	"type": "resource_link",
	"uri": "gym://equipment/vault-002",
	"name": "Vault Table",
	"description": "Gymnastics Equipment: Vault Table",
	"mimeType": "application/json"
}
This is ideal for lists, large resources, or when you want to let the client decide what to fetch.

What You'll Do in This Exercise

You'll update your EpicMe journaling app's tools to:
  1. Embed resources in tool responses (e.g., have get_entry return the entry as an embedded resource).
  2. Link to resources in tool responses (e.g., have list_entries and list_tags return resource links for each entry/tag).
By the end, your tools and resources will work hand-in-hand, enabling richer, more actionable results for clients and LLMs.
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