@decocms/runtime

Provides the framework for building MCP applications behind Studio with typed tools, bindings, authentication, OAuth, resources, prompts, and triggers.

| Attribute | Value | | --- | --- | | Workspace | @decocms/runtime (packages/runtime) | | Kind | Public MCP application framework | | Runtime | Node.js 24+; Web Fetch API | | Distribution | Public npm package |

Overview

@decocms/runtime is the application-facing runtime for MCP servers connected to Studio. It turns declarative tools, prompts, resources, agents, and bindings into a Fetch-compatible handler. The runtime also supplies the request-scoped Studio context that application code uses for identity, connection metadata, credentials, and calls to bound MCPs.

The package exposes source TypeScript through explicit package subpaths. Consumers should import only the subpath that owns the capability they need.

Responsibilities

• Create MCP tools with Zod input and output schemas.
• Mount tools, prompts, resources, and event handlers on a Fetch-compatible MCP server.
• Resolve Studio request context and bound connections for each request.
• Enforce authenticated access to protected tools, prompts, and resources.
• Serve OAuth metadata and OAuth routes when an OAuth configuration is present.
• Expose scoped access to Studio-managed credentials through the vault client.
• Create trigger-management tools and deliver trigger callbacks to Studio.
• Provide helpers for connection proxies, MCP client stubs, assets, and Decopilot applications.

Usage

Install the package in an MCP application:

bun add @decocms/runtime

Define a tool and export the runtime handler:

import {
  withRuntime,
} from "@decocms/runtime";
import {
  createTool,
  ensureAuthenticated,
} from "@decocms/runtime/tools";
import { z } from "zod";

const greet = createTool({
  id: "GREET",
  description: "Greet the signed-in user",
  inputSchema: z.object({
    name: z.string(),
  }),
  outputSchema: z.object({
    message: z.string(),
  }),
  execute: async ({ context, runtimeContext }) => {
    const user = ensureAuthenticated(runtimeContext);

    return {
      message: `Hello, ${context.name}. Signed in as ${user.email}.`,
    };
  },
});

export default withRuntime({
  tools: [greet],
});

withRuntime() returns an object with a fetch() handler. It serves the MCP endpoint at /mcp, delegates any unmatched request to the optional application fetch handler, and applies the configured CORS and OAuth behavior.

Prompts and resources use the same request context:

import { createPrompt, createResource } from "@decocms/runtime";
import { z } from "zod";

const reviewPrompt = createPrompt({
  name: "review",
  description: "Review a change",
  argsSchema: {
    path: z.string().optional(),
  },
  execute: ({ args }) => ({
    messages: [
      {
        role: "user",
        content: {
          type: "text",
          text: `Review ${args.path ?? "the current change"}.`,
        },
      },
    ],
  }),
});

const statusResource = createResource({
  uri: "studio://status",
  name: "Status",
  mimeType: "application/json",
  read: () => ({
    uri: "studio://status",
    mimeType: "application/json",
    text: JSON.stringify({ ready: true }),
  }),
});

createPrompt() and createResource() protect their handlers by default. Use the explicit createPublicPrompt() or createPublicResource() variants only when the content is safe to expose without a Studio identity.

Architecture

withRuntime() is the composition root. For each incoming request it:

1. Normalizes canonical Studio environment fields and supported legacy aliases.
2. Creates a request-scoped context containing identity and binding state.
3. Initializes configured bindings.
4. Dispatches MCP requests to the server created from tools, prompts, resources, agents, and event handlers.
5. Applies OAuth and CORS behavior around the result.
6. Falls back to the application's own fetch() handler for non-runtime routes.

The request context is stored with asynchronous request scoping. Tool code receives that context as the second execute() argument; it should not read ambient HTTP objects or reconstruct Studio identity from process-wide state.

Bindings describe MCP capabilities that a connection implements. withBindings() resolves those bindings for a request, while BindingOf, AgentOf, and proxyConnectionForId() provide typed access patterns for consumers that need to call them.

Development

Run package checks from the repository root:

bun run --cwd=packages/runtime check
bun run --cwd=packages/runtime test

Run a focused test file while iterating:

bun test packages/runtime/src/tools.test.ts

Format and lint repository changes before committing:

bun run fmt
bun run lint

Boundaries

• This package is an MCP application framework, not the Studio control plane. It must not import server implementation details from apps/api or UI details from apps/web.
• Treat the request-scoped runtime context as the authority for identity, Studio metadata, and bound services. Do not cache it across requests.
• A tool is not protected merely because it runs behind an MCP endpoint. Call ensureAuthenticated() in tools that require a user.
• Prompts and resources are authenticated by default. Public variants must expose only non-sensitive data.
• Credential access is opt-in and scope-limited. Never request more credential material than the application needs, and never persist returned secrets.
• The published package requires Node.js 24 or newer. Individual helpers use Web Fetch APIs; environment-specific helpers such as file-backed trigger storage and the asset server also require their documented host capabilities.
• Legacy MESH_* environment fields and meshUrl remain compatibility aliases. New code must use STUDIO_* names and studioUrl.

Export surface

| Import | Purpose | | --- | --- | | @decocms/runtime | Runtime composition, prompts, resources, bindings, request context, MCP stubs, and the Studio vault client | | @decocms/runtime/proxy | MCP proxy client primitives | | @decocms/runtime/client | Client for the runtime tool-call HTTP endpoint | | @decocms/runtime/bindings | Binding declarations, registry helpers, and binding initialization | | @decocms/runtime/asset-server | Static and single-page-application asset serving | | @decocms/runtime/tools | Tool creation plus prompt, resource, agent, and authentication primitives | | @decocms/runtime/decopilot | Decopilot application helpers | | @decocms/runtime/triggers | Trigger definitions, configuration tools, and callback delivery | | @decocms/runtime/trigger-storage | In-memory, Studio KV, and JSON-file trigger storage adapters |

These are the only supported package entry points. Do not import files below @decocms/runtime/src.

Authentication and credential access

ensureAuthenticated(runtimeContext) returns the Studio user or throws when the request is unauthenticated. It is the normal guard for a protected tool.

Applications that need Studio-managed credentials declare an explicit binding-scoped permission and create a client from the bootstrap passed to configuration.onInstall or configuration.onChange:

import {
  CREDENTIAL_ACCESS_TOKEN_READ_SCOPE,
  createStudioVaultClient,
  type ConfigurationScope,
} from "@decocms/runtime";
import type { StudioVaultBootstrap } from "@decocms/runtime/tools";

const scopes = [
  `github::${CREDENTIAL_ACCESS_TOKEN_READ_SCOPE}`,
] satisfies ConfigurationScope[];

function vaultClient(bootstrap: StudioVaultBootstrap) {
  return createStudioVaultClient({
    baseUrl: bootstrap.baseUrl,
    org: bootstrap.org,
    token: bootstrap.token,
  });
}

Use CREDENTIAL_ACCESS_TOKEN_READ_SCOPE for a provider access token and CREDENTIAL_CONFIGURATION_READ_SCOPE for non-token credential configuration. Refresh tokens and OAuth client secrets stay inside the Studio vault and are not part of the application-facing contract.

Triggers and persistence

createTriggers() creates TRIGGER_LIST and TRIGGER_CONFIGURE tools from typed trigger definitions. Its notify() method is intentionally fire-and-forget: delivery failures are logged and are not thrown back into a webhook handler.

Trigger configuration is process-local unless the application supplies a TriggerStorage. Use StudioKV when Studio KV is available, JsonFileStorage only for an appropriate local Node/Bun deployment, or provide an adapter backed by the application's durable store.

Configuration, bindings, and events

configuration.state accepts a Zod schema for persisted MCP configuration. BindingOf() fields in that schema resolve configured connection references into typed clients on STUDIO_REQUEST_CONTEXT.state. Declare required permissions in configuration.scopes; Studio evaluates those scopes when it configures the connection.

configuration.onChange runs for configuration updates and receives the parsed state, granted scopes, and optional vault bootstrap. configuration.onInstall runs on the first saved configuration and also receives the agent-provisioning helper. Handlers must be idempotent because network or deployment failures can interrupt work around these callbacks.

events.handlers declares CloudEvent subscriptions by binding key or SELF. The runtime exposes the corresponding ON_EVENTS tool and supports both batch results and per-event results. Event handlers own their idempotency because the Studio event bus provides at-least-once delivery.

When oauth is configured, the runtime serves protected-resource metadata, authorization-server metadata, authorization, callback, token, and dynamic client registration routes. The application supplies provider-specific authorization and token-exchange behavior.

The optional cors property controls runtime CORS handling; set it to false to disable the built-in layer. The optional application fetch() handler receives requests that do not match the runtime, OAuth, or tool-call routes.

Related documentation

• Bindings guide
• Repository guidelines
• Testing strategy