Slack MCP Server

Instructions

Implementation Reference

• src/tools/files.ts:4-25 (handler)

  The main handler function for the 'upload_file' tool. It validates the input arguments using uploadFileSchema and uploads the file content to specified Slack channels using the files.uploadV2 API, returning the file object.

  export async function uploadFile(client: SlackClientWrapper, args: unknown) {
    const params = uploadFileSchema.parse(args);
  
    return await client.safeCall(async () => {
      const result = await client.getClient().files.uploadV2({
        channels: params.channels.join(','),
        content: params.content,
        filename: params.filename,
        title: params.title,
        initial_comment: params.initial_comment,
      });
  
      const maybeFile = (result && typeof result === 'object' && 'file' in result)
        ? (result as { file?: unknown }).file
        : undefined;
  
      return {
        ok: true,
        file: maybeFile,
      };
    });
  }

• src/utils/validators.ts:86-92 (schema)

  Zod schema for input validation of the upload_file tool, defining required channels array, content, filename, and optional title and initial_comment.

  export const uploadFileSchema = z.object({
    channels: z.array(channelIdSchema).min(1),
    content: z.string().min(1),
    filename: z.string().min(1),
    title: z.string().optional(),
    initial_comment: z.string().optional(),
  });

• src/index.ts:318-350 (registration)

  MCP tool registration in the list_tools response, defining the name, description, and inputSchema for 'upload_file'.

  {
    name: 'upload_file',
    description: 'Upload a file to Slack',
    inputSchema: {
      type: 'object',
      properties: {
        channels: {
          type: 'array',
          items: {
            type: 'string',
          },
          description: 'Array of channel IDs to share the file to',
        },
        content: {
          type: 'string',
          description: 'File content',
        },
        filename: {
          type: 'string',
          description: 'Filename',
        },
        title: {
          type: 'string',
          description: 'File title',
        },
        initial_comment: {
          type: 'string',
          description: 'Initial comment',
        },
      },
      required: ['channels', 'content', 'filename'],
    },
  },

• src/index.ts:434-434 (registration)

  Registration of the upload_file handler in the internal tool dispatch map, mapping the tool name to the fileTools.uploadFile function.

  upload_file: (args) => fileTools.uploadFile(slackClient, args),