opencode-slim-mcp

OpenCode plugin that converts MCP servers marked slim: true into skills + a single native proxy tool. Agent discovers tools via on-demand skill loading (zero idle token cost), calls them through a pooled MCP connection.

Problem

• Full MCP registration = token bloat (hundreds of schemas in context)
• No middle ground between full registration and blind proxying

How to Install

1. Add the plugin to your opencode.json

{
  "plugin": ["opencode-slim-mcp"]
}

2. Mark MCP servers with slim: true

In your project or global opencode.json, add "slim": true to any MCP server you want managed by this plugin:

{
  "mcp": {
    "todoist": {
      "command": "npx",
      "args": ["-y", "@anthropics/todoist-mcp"],
      "slim": true
    },
    "playwright": {
      "command": "npx",
      "args": ["-y", "@anthropics/playwright-mcp"],
      "slim": true
    },
    "regular-mcp": {
      "command": "some-mcp-server",
      "args": ["--stdio"]
    }
  }
}

Servers without slim: true are left untouched — opencode handles them normally.

3. (Optional) Disable a slim server

Set "enabled": false to disable a server without removing it from config:

{
  "mcp": {
    "todoist": {
      "command": "npx",
      "args": ["-y", "@anthropics/todoist-mcp"],
      "slim": true,
      "enabled": false
    }
  }
}

Disabled servers appear as [disabled] in mcp-status but won't start, generate skills, or accept tool calls.

What Happens on Startup

1. Plugin reads opencode.json (project dir + ~/.config/opencode/)
2. Extracts entries with slim: true (skips disabled ones)
3. Introspects each server for available tools
4. Generates SKILL.md files + schema cache per server
5. Registers a single mcp tool that proxies calls to any slim server
6. Probes remote reachability first; auth failures stay enabled for opencode mcp auth
7. Sets enabled: false on remaining slim entries in host config (prevents double-handling)

Regeneration only triggers when the enabled server list changes.

Plugin Configuration

Create slim-mcp-config.json in your project root or ~/.config/opencode/:

{
  "lazy-loading": true,
  "lazy-idle-shutdown-interval": "5m"
}

| Option | Default | Description | |--------|---------|-------------| | lazy-loading | true | Connect to servers on first tool call (vs. eagerly on startup) | | lazy-idle-shutdown-interval | "5m" | Disconnect idle servers after this duration (e.g. "5m", "300000") |

Tools Provided

mcp

Calls a tool on any enabled slim MCP server.

mcp(server: "todoist", tool: "add-tasks", params: '{"tasks": [...]}')

mcp-status

Shows status of all slim MCP servers: connected, pending, disabled, or error.

Output Structure

~/.local/state/opencode/slim-mcp/
├── skills/mcp-<server>/SKILL.md     # Tool names, descriptions, param docs
├── schemas/<server>/*.json           # Per-tool input schemas
├── manifest.json                     # Generation metadata
└── status.json                       # Server status (consumed by TUI plugin)

TUI Sidebar Plugin

Shows slim MCP server status in the opencode TUI sidebar (connection state, errors, auth status).

Add to your global TUI config at ~/.config/opencode/tui.json:

{
  "$schema": "https://opencode.ai/tui.json",
  "plugin": ["opencode-slim-mcp"]
}

Renders below the built-in MCP sidebar (order 210). Polls status.json on startup + after mcp/mcp-status tool calls.

Prerequisites

• Node.js (ESM)
• MCP servers must be reachable via their configured command/args