Agent-Native Devframe

Experimental

The agent-native surface (agent field on defineRpcFunction, DevToolsAgentHost, and the devframe/adapters/mcp adapter) is experimental and may change without a major version bump until it stabilizes.

Devframe can expose the same surface the browser DevTools UI consumes — RPC functions, resources, and shared state — to coding agents (Claude Desktop / Cursor / Zed / Claude Code, or any MCP-speaking client). Agent exposure is opt-in per function; functions stay private by default.

How it works

Three building blocks:

1. An agent field on defineRpcFunction. Add agent: { description, ... } to opt a function in. Functions without the field stay private.
2. ctx.agent — a host exposed on DevToolsNodeContext. Plugins register tools that aren't backed by an RPC, and expose readable resources (e.g. a Markdown build summary).
3. The MCP adapter (devframe/adapters/mcp) — translates the agent host into a Model Context Protocol server, currently over stdio.

Exposing an RPC function

import { defineRpcFunction } from 'devframe'

export const getSessionSummary = defineRpcFunction({
  name: 'rolldown-get-session-summary',
  type: 'query',
  args: [v.object({ sessionId: v.string() })],
  returns: v.object({ durationMs: v.number(), chunkCount: v.number() }),
  agent: {
    description: 'Summarize a Rolldown build session. Safe to call freely.',
    title: 'Build summary',
    // safety inferred from `type: 'query'` → 'read'
  },
  setup: ctx => ({
    handler: async ({ sessionId }) => {
      // ...
    },
  }),
})

Agent tools take a single object input. The MCP adapter synthesises arg0, arg1, … from positional args (args: [A, B]); a single object schema (args: [v.object({ ... })]) reads better at the agent boundary because property names are self-describing.

Registering a plugin tool

For tools without a matching RPC — say, an on-demand narrative summary — register them directly:

export default defineDevtool({
  id: 'my-plugin',
  setup(ctx) {
    ctx.agent.registerTool({
      id: 'my-plugin:summarize',
      description: 'Plain-text summary of the current build state.',
      safety: 'read',
      handler: async () => ({
        markdown: buildSummary(),
      }),
    })
  },
})

Registering a resource

Resources surface readable snapshots of state, identified by URI:

ctx.agent.registerResource({
  id: 'current-session',
  name: 'Current Rolldown session',
  description: 'Markdown snapshot of the active build session.',
  mimeType: 'text/markdown',
  read: () => ({ text: renderMarkdown(currentSession) }),
})

Every ctx.rpc.sharedState key is also automatically exposed to MCP as devframe://state/<key>. Pass exposeSharedState: false (or a filter function) to createMcpServer to opt out.

Starting the MCP server

The simplest path is the CLI:

# Run your devtool with an MCP stdio server attached.
devframe mcp

Programmatic equivalent:

import { defineDevtool } from 'devframe'
import { createMcpServer } from 'devframe/adapters/mcp'

const devtool = defineDevtool({ /* … */ })

await createMcpServer(devtool, { transport: 'stdio' })

@modelcontextprotocol/sdk is a peer dependency — add it to your package when you want to ship an MCP-enabled devtool.

Connecting Claude Desktop

Add an entry to claude_desktop_config.json:

{
  "mcpServers": {
    "my-devtool": {
      "command": "pnpm",
      "args": ["--filter", "my-devtool", "exec", "devframe", "mcp"]
    }
  }
}

Restart Claude Desktop. The tools you flagged with agent: { ... } (plus any registerTool calls) show up in the MCP tool drawer. Resources are reachable as devframe://resource/<id> and devframe://state/<key> URIs.

Safety model

• Opt-in exposure. Functions opt in via the agent field; everything else stays private.
• safety — one of 'read', 'action', 'destructive'. Inferred from the RPC type (static/query → read, action/event → action), with explicit override available.
• The MCP adapter maps safety to tool annotations (readOnlyHint, destructiveHint). MCP clients use these to decide whether to prompt for confirmation before calling.

CLI

Command	Description
devframe mcp	Start an MCP server on stdio.