@Resource

@Resource(options)
class MyResource extends ResourceContext {
  async execute(uri) { /* ... */ }
}

Reference

@Resource(options)

Apply @Resource to a class that extends ResourceContext, and list the class in an app's resources array.

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({
  name: "sla",
  uri: "policy://sla",
  description: "How fast the help desk replies, by ticket priority",
  mimeType: "application/json",
})
class SlaPolicy extends ResourceContext {
  async execute() {
    return { high: "4 hours", normal: "1 business day", low: "3 business days" };
  }
}

See more examples below.

Options

Required:

Optional:

execute(uri, params)

FrontMCP calls execute() every time a client reads the resource.

• uri: the URI that was read. For a @Resource, that's always its uri option.
• params: template parameters. Always {} for a @Resource.
• Returns the content. FrontMCP turns it into the contents array of the resources/read result:

Inside execute(), this is the ResourceContext: this.uri and this.params hold the same values as the arguments, this.get() returns providers, this.fetch() makes outbound HTTP requests, this.context and this.auth describe the request and the caller, and this.notifyUpdated() tells subscribed clients that the content changed. this.notify(), this.progress() and this.elicit() belong to tools, not resources.

resource(options)(handler)

The function form takes the same options. The handler receives (uri, params) and returns a ReadResourceResult, the { contents: [...] } shape.

Caveats

• The class must extend ResourceContext. Using @Resource on any other class is a compile error.
• uri must have a scheme followed by ://. Otherwise the server doesn't start, and reports "URI must have a valid scheme".
• Reads match the URI exactly. policy://sla/ and policy://SLA are different URIs, and reading them fails with "Resource not found".
• A resource takes no arguments. For data that depends on an id, use @ResourceTemplate. If a resource and a template both match a URI, the resource wins.
• If execute() throws ResourceNotFoundError(uri), the client gets the same error as for a URI that matches nothing: -32602, Resource not found: …. A PublicMcpError also gives -32602, with your error's message as the whole message.
• Any other error is an internal one: JSON-RPC error -32603, with Resource "…" read failed: and your error's message in development. With NODE_ENV=production, FrontMCP hides the message and sends Internal FrontMCP error. Please contact support with error ID: … instead. See troubleshooting.
• this.fail(error) fails the read the same way as throw error for a PublicMcpError. For any other error it's still -32603, but the message is your error's message without the read failed: prefix, and data.code is SERVER_ERROR instead of RESOURCE_READ_ERROR. Production hides it the same way.

Usage

Exposing data at a fixed URI

Give the resource a URI with your own scheme and a description that says what's in it. Return a plain object and FrontMCP sends it as JSON.

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({
  name: "sla",
  title: "Reply-time policy",
  uri: "policy://sla",
  description: "How fast the help desk replies, by ticket priority. Read it before promising a customer a reply time.",
})
export class SlaPolicy extends ResourceContext {
  async execute() {
    return { high: "4 hours", normal: "1 business day", low: "3 business days" };
  }
}

Open the Capabilities tab to see the resource as resources/list describes it. Clients read it with resources/read and the URI.

Choosing what the client receives

What execute() returns decides the content blocks and their MIME types.

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({ name: "reply-guide", uri: "guide://replies.md", description: "How to word replies to customers" })
export class ReplyGuide extends ResourceContext {
  async execute() {
    return "# Replying to customers\n\n- Greet them by name.\n- Say what you did, then what happens next.\n- Link the ticket id, like T-1.";
  }
}

Reading from a provider

Get shared services with this.get(), and register the provider in the same app's providers array.

import { Resource, ResourceContext } from "@frontmcp/sdk";
import { Rota } from "./rota";

@Resource({ name: "on-duty", uri: "desk://on-duty", description: "Which agents are on duty right now" })
export class OnDuty extends ResourceContext {
  async execute() {
    return { agents: this.get(Rota).onDuty() };
  }
}

Describing a resource for clients

Everything except availableWhen goes out in resources/list. Clients use title and icons for display, and annotations to decide who the content is for and how prominent it should be. The test below reads the list the way a client would.

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({
  name: "sla",
  title: "Reply-time policy",
  uri: "policy://sla",
  description: "How fast the help desk replies, by ticket priority",
  mimeType: "application/json",
  annotations: { audience: ["assistant"], priority: 0.8, lastModified: "2026-09-01T09:00:00Z" },
  _meta: { "com.example/owner": "support-ops" },
})
export class SlaPolicy extends ResourceContext {
  async execute() {
    return { high: "4 hours", normal: "1 business day", low: "3 business days" };
  }
}

Writing a resource as a function

For a resource that doesn't need context, the function form is shorter. Its handler returns the full { contents } shape, which is sent as it is, so set each block's mimeType there.

import { resource } from "@frontmcp/sdk";

export const openingHours = resource({
  name: "opening-hours",
  uri: "policy://hours",
  mimeType: "application/json",
  description: "When the help desk answers tickets",
})((uri) => ({
  contents: [{ uri, mimeType: "application/json", text: JSON.stringify({ weekdays: "08:00-18:00", weekends: "closed" }) }],
}));

Troubleshooting

The server doesn't start: "URI must have a valid scheme"

The uri option needs a scheme followed by ://. policy:sla and /policy/sla are rejected; policy://sla works.

Reads fail with -32602 "Resource not found"

No resource or template matches the URI exactly, or execute() threw ResourceNotFoundError. Check for a trailing slash, different letter case, or a typo, and compare with resources/list. Under MCP 2026-07-28 this error has code -32602; earlier protocol versions use -32002. A resource whose availableWhen.surface leaves out "mcp" gets the same answer: MCP clients can't read it.

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({ name: "sla", uri: "policy://sla" })
export class SlaPolicy extends ResourceContext {
  async execute() {
    return { high: "4 hours" };
  }
}

Reads fail with -32603 "Resource … read failed"

execute() threw an error that isn't a PublicMcpError, so FrontMCP treats it as a failure of the server. In development, the message after read failed: is your error's message:

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({ name: "sla", uri: "policy://sla" })
export class SlaPolicy extends ResourceContext {
  async execute(): Promise<unknown> {
    // 🚩 A server failure, and production hides the message
    throw new Error("The SLA policy hasn't been published yet");
  }
}

With NODE_ENV=production, the client only gets Internal FrontMCP error. Please contact support with error ID: …. If the client should read the message, throw a PublicMcpError. The read then fails with -32602 and your message, in production too:

import { PublicMcpError, Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({ name: "sla", uri: "policy://sla" })
export class SlaPolicy extends ResourceContext {
  async execute(): Promise<unknown> {
    // ✅ The client sees exactly this message
    throw new PublicMcpError("The SLA policy hasn't been published yet");
  }
}

A message ending in read failed: Resource output not found means execute() returned nothing. Return the content, or end with this.respond(), which works in resources since 1.9.3.

Reads fail with -32003 "Resource "…" is not available in the current environment"

The resource's availableWhen doesn't match where the server runs. It's left out of resources/list, and a client that reads it by URI gets this error, with what the resource requires and what the server is:

import { Resource, ResourceContext } from "@frontmcp/sdk";

@Resource({ name: "deploy-notes", uri: "policy://deno-deploy", mimeType: "text/plain", availableWhen: { runtime: ["deno"] } })
export class DeployNotes extends ResourceContext {
  async execute() {
    return "Deploy with deployctl.";
  }
}

The message lists the server's OS, runtime and deployment, in production too. If the resource should be readable here, fix its availableWhen.

My resource isn't in resources/list

Check, in order:

1. The class is in its app's resources array, and the app is in @FrontMcp({ apps }).
2. It's a @Resource. Templates are listed separately, in resources/templates/list.
3. Its availableWhen matches the environment the server runs in.