implementing-mcp-resources

Implementing MCP Resources

Workflow

Task Progress:
- [ ] Step 1: Create resource file in src/mcp/resources/
- [ ] Step 2: Define name, URI/template, config, and readCallback
- [ ] Step 3: Export as default ResourcePlugin or ResourceTemplatePlugin
- [ ] Step 4: Register in src/mcp/resources/mod.ts
- [ ] Step 5: (If KV-backed) Add URI-to-key mapping in kvKeys.ts
- [ ] Step 6: Run `deno task ci` to verify

Resource Types

Type	Use Case	URI	Plugin Type
Static resource	Fixed content at a known URI	"hello://world"	ResourcePlugin
KV-backed resource	Persistent, mutable state	"counter://value"	ResourcePlugin
Resource template	Dynamic URI with variables	"greetings://{name}"	ResourceTemplatePlugin

Static Resource Template

Create a new file in src/mcp/resources/.

import type { ResourceMetadata } from "@modelcontextprotocol/sdk/server/mcp.js";
import type { ReadResourceResult } from "@modelcontextprotocol/sdk/types.js";

import type { ResourcePlugin } from "$/shared/types.ts";

const name = "myResource";

const uri = "my-scheme://my-path";

const config: ResourceMetadata = {
  description: "What this resource provides",
  mimeType: "text/plain",  // or "application/json"
};

async function readCallback(): Promise<ReadResourceResult> {
  return {
    contents: [{
      uri,
      text: "Resource content here",
    }],
  };
}

const module: ResourcePlugin = {
  type: "resource",
  name,
  uri,
  config,
  readCallback,
};

export default module;

Resource Template (Dynamic URI)

For resources with variable URI segments like greetings://{name}:

import {
  type CompleteResourceTemplateCallback,
  type ResourceMetadata,
  ResourceTemplate,
} from "@modelcontextprotocol/sdk/server/mcp.js";
import type { ReadResourceResult } from "@modelcontextprotocol/sdk/types.js";

import type { ResourceTemplatePlugin } from "$/shared/types.ts";

const name = "myTemplate";

const completeName: CompleteResourceTemplateCallback = (value) => {
  const prefix = value.trim().toLowerCase();
  return suggestions.filter((s) => s.toLowerCase().startsWith(prefix)).slice(0, 5);
};

const template = new ResourceTemplate(
  "my-scheme://{variable}",
  {
    list: undefined,               // optional: callback to list all instances
    complete: { variable: completeName },  // optional: autocomplete per variable
  },
);

const config: ResourceMetadata = {
  mimeType: "text/plain",
};

async function readCallback(
  uri: URL,
  variables: Record<string, unknown>,
): Promise<ReadResourceResult> {
  const variable = variables.variable as string;
  return {
    contents: [{
      uri: uri.toString(),
      text: `Content for ${variable}`,
    }],
  };
}

const module: ResourceTemplatePlugin = {
  type: "template",
  name,
  template,
  config,
  readCallback,
};

export default module;