MCP Resources

Resources provide data that language models can access. Each resource has a URI, name, MIME type, and a data provider function.

Resource Structure

Every resource in ModelContextProtocol.jl is represented by the MCPResource struct:

  • uri: Unique URI identifier for the resource
  • name: Human-readable resource name
  • description: Explanation of the resource's purpose
  • mime_type: Content type (e.g., "application/json", "text/plain")
  • data_provider: Function that returns the resource's data
  • annotations: Optional metadata about the resource

Creating Resources

Here's how to create a basic resource:

using URIs

weather_resource = MCPResource(
    uri = "weather://current",
    name = "Current Weather",
    description = "Current weather conditions",
    mime_type = "application/json",
    data_provider = () -> Dict(
        "temperature" => 22.5,
        "conditions" => "Partly Cloudy",
        "updated" => Dates.format(now(), "yyyy-mm-dd HH:MM:SS")
    )
)

Note: The uri field accepts both strings and URI objects. Strings are automatically converted to URIs.

Data Providers

The data_provider function can return different types of data:

  1. For simple data (automatically serialized to JSON):

    • Return Julia objects (Dict, Array, etc.) that can be JSON-serialized
    • These are wrapped in TextResourceContents with JSON serialization

  2. For explicit control over content:

    • Return TextResourceContents for text data
    • Return BlobResourceContents for binary data

The data_provider receives the requested URI as a parameter when using wildcards.

Registering Resources

Resources can be registered with a server in two ways:

  1. During server creation:
server = mcp_server(
    name = "my-server",
    resources = my_resource  # Single resource or vector of resources
)
  1. After server creation:
register!(server, my_resource)

Directory-Based Organization

Resources can be organized in directory structures and auto-registered:

my_server/
└── resources/
    ├── weather.jl
    └── stock_data.jl

Each file should export one or more MCPResource instances:

# weather.jl
using ModelContextProtocol
using Dates

weather_resource = MCPResource(
    uri = "weather://current",
    name = "Current Weather",
    description = "Current weather conditions",
    mime_type = "application/json",
    data_provider = () -> Dict(
        "temperature" => 22.5,
        "conditions" => "Partly Cloudy",
        "updated" => Dates.format(now(), "yyyy-mm-dd HH:MM:SS")
    )
)

Then auto-register from the directory:

server = mcp_server(
    name = "my-server",
    auto_register_dir = "my_server"
)

Advanced Examples

Resource with Dynamic URI Patterns

# Support URIs like file://path/to/file.txt
file_resource = MCPResource(
    uri = "file://*",
    name = "File System Access",
    description = "Access local files",
    mime_type = "text/plain",
    data_provider = function(uri::String)
        # Extract path from URI
        path = replace(uri, "file://" => "")
        
        if isfile(path)
            content = read(path, String)
            return TextResourceContents(
                uri = uri,
                text = content,
                mime_type = "text/plain"
            )
        else
            error("File not found: $path")
        end
    end
)

Resource with Binary Data

image_resource = MCPResource(
    uri = "images://logo",
    name = "Logo Image",
    description = "Company logo",
    mime_type = "image/png",
    data_provider = function(uri::String)
        image_data = read("logo.png")  # Returns Vector{UInt8}
        return BlobResourceContents(
            uri = uri,
            blob = image_data,
            mime_type = "image/png"
        )
    end
)