@slackwire/mcp

A Model Context Protocol (MCP) server over @slackwire/core. It exposes the same Slack operations the CLI uses (post, morph, react, upload, resolve names) as MCP tools, so an MCP-capable assistant can drive Slack through tool calls instead of a shell. The package is a library: it provides createMcpServer(slackClient, resolver), and you supply the transport (typically stdio).

Version 0.1.0. Requires Node.js 20 or newer.

Install

pnpm add @slackwire/mcp

Running it

Construct a SlackClient and Resolver from @slackwire/core, create the server, and connect a transport. The server runs until the transport closes. Diagnostic logs go to stderr, prefixed [slackwire-mcp].

import { createMcpServer } from '@slackwire/mcp';
import { SlackClient, Resolver } from '@slackwire/core';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';

const client = new SlackClient(process.env.SLACK_TOKEN!);
const resolver = new Resolver(/* web client */, /* cache */, process.env.SLACK_TEAM_ID ?? 'T000');

const server = createMcpServer(client, resolver);
await server.connect(new StdioServerTransport());

Wire it into an MCP host that launches your stdio entry point:

{
  "mcpServers": {
    "slackwire": {
      "command": "node",
      "args": ["path/to/your-mcp-entry.js"],
      "env": { "SLACK_TOKEN": "xoxb-...", "SLACK_TEAM_ID": "T0XXXXXXXXX" }
    }
  }
}

Public API surface

createMcpServer(slackClient, resolver): McpServerHandle

Creates and configures the server. It does not listen until connect() is called.

interface McpServerHandle {
  connect(transport: Transport): Promise<void>;
  close(): Promise<void>;
}

Tools exposed

| Tool | Required inputs | Optional inputs | Returns | |---|---|---|---| | post_card | channel, blocks (JSON string) | text | { ts, channel, permalink } | | update_card | channel, ts, blocks (JSON string) | text | { ts, channel } | | post | channel, text | (none) | { ts, channel } | | react | channel, ts, name | (none) | "ok" | | upload | channel, filename, content | (none) | "ok" | | resolve | name, type ("channel" or "user") | (none) | { name, type, id } |

Every channel input accepts a channel name or a Slack ID; names are resolved to an ID via the injected Resolver before each call. blocks is passed as a JSON-encoded string so the tool schema stays type: string and avoids nesting issues with arbitrary block shapes. post_card returns a permalink of the form https://slack.com/archives/<channel>/p<ts>. react expects the emoji name without colons. resolve returns id: null when the name cannot be resolved.

Limits and gotchas

• blocks must be a JSON-encoded array for post_card and update_card. A non-JSON or non-array value is rejected with an isError tool response (Invalid blocks: ...), not a thrown exception.
• The MCP server does no template rendering and no per-kind escaping, but it does re-validate: post_card and update_card run validateStructural and validateLimits on the parsed blocks before sending, and a structure or Slack-limit violation comes back as a Validation error: ... tool response. Render and escape with @slackwire/core's render() first, then pass the resulting blocks; the tools forward them unchanged once validation passes.
• Name resolution and its caching are entirely the responsibility of the Resolver you inject.
• The accent / attribution footer is off by default and is a render-time concern in @slackwire/core, not something these tools add.
• Errors thrown inside a tool handler surface to the calling agent as MCP error responses.

See the root README for the overall project.