Tmux MCP Server

Instructions

Implementation Reference

• src/index.ts:500-525 (handler)

  The handler function that implements the core logic of tmux_split_window by constructing and executing the appropriate tmux split-window command using helpers formatTarget and runTmux.

  async ({ session, window, horizontal, start_directory, percentage }) => {
    try {
      const target = formatTarget(session, window);
      let cmd = `split-window -t "${target}"`;
      if (horizontal) {
        cmd += " -h";
      }
      if (start_directory) {
        cmd += ` -c "${start_directory}"`;
      }
      if (percentage) {
        cmd += ` -p ${percentage}`;
      }
      await runTmux(cmd);
  
      return {
        content: [{ type: "text", text: `Window split ${horizontal ? "horizontally" : "vertically"} successfully.` }],
        structuredContent: { success: true, session, window, horizontal },
      };
    } catch (error) {
      return {
        content: [{ type: "text", text: error instanceof Error ? error.message : String(error) }],
        isError: true,
      };
    }
  }

• src/index.ts:484-492 (schema)

  Zod input schema defining parameters for the tmux_split_window tool: session (required), window (optional), horizontal (default false), start_directory (optional), percentage (1-99 optional).

  inputSchema: z
    .object({
      session: z.string().min(1).describe("Name of the session"),
      window: z.union([z.string(), z.number()]).optional().describe("Window index or name"),
      horizontal: z.boolean().default(false).describe("Split horizontally (default: vertical)"),
      start_directory: z.string().optional().describe("Starting directory for the new pane"),
      percentage: z.number().min(1).max(99).optional().describe("Size of new pane as percentage"),
    })
    .strict(),

• src/index.ts:472-526 (registration)

  Registration of the tmux_split_window tool with McpServer, including metadata, schema, and handler reference.

  server.registerTool(
    "tmux_split_window",
    {
      title: "Split tmux Window",
      description: `Split a window into panes.
  
  Args:
    - session (string, required): Name of the session
    - window (string or number, optional): Window index or name
    - horizontal (boolean, optional): Split horizontally (default: false = vertical split)
    - start_directory (string, optional): Starting directory for the new pane
    - percentage (number, optional): Size of new pane as percentage (1-99)`,
      inputSchema: z
        .object({
          session: z.string().min(1).describe("Name of the session"),
          window: z.union([z.string(), z.number()]).optional().describe("Window index or name"),
          horizontal: z.boolean().default(false).describe("Split horizontally (default: vertical)"),
          start_directory: z.string().optional().describe("Starting directory for the new pane"),
          percentage: z.number().min(1).max(99).optional().describe("Size of new pane as percentage"),
        })
        .strict(),
      annotations: {
        readOnlyHint: false,
        destructiveHint: false,
        idempotentHint: false,
        openWorldHint: false,
      },
    },
    async ({ session, window, horizontal, start_directory, percentage }) => {
      try {
        const target = formatTarget(session, window);
        let cmd = `split-window -t "${target}"`;
        if (horizontal) {
          cmd += " -h";
        }
        if (start_directory) {
          cmd += ` -c "${start_directory}"`;
        }
        if (percentage) {
          cmd += ` -p ${percentage}`;
        }
        await runTmux(cmd);
  
        return {
          content: [{ type: "text", text: `Window split ${horizontal ? "horizontally" : "vertically"} successfully.` }],
          structuredContent: { success: true, session, window, horizontal },
        };
      } catch (error) {
        return {
          content: [{ type: "text", text: error instanceof Error ? error.message : String(error) }],
          isError: true,
        };
      }
    }
  );

• src/index.ts:70-82 (helper)

  Helper function used by the handler to construct the tmux target string (e.g., session:window.pane).

  function formatTarget(session?: string, window?: number | string, pane?: number): string {
    let target = "";
    if (session) {
      target = session;
      if (window !== undefined) {
        target += `:${window}`;
        if (pane !== undefined) {
          target += `.${pane}`;
        }
      }
    }
    return target;
  }

• src/index.ts:45-68 (helper)

  Core utility function used by all tmux tools, including tmux_split_window, to execute tmux commands asynchronously with custom error messages.

  async function runTmux(args: string): Promise<string> {
    try {
      const { stdout } = await execAsync(`tmux ${args}`);
      return stdout.trim();
    } catch (error: unknown) {
      if (error instanceof Error && "stderr" in error) {
        const stderr = (error as { stderr: string }).stderr;
        if (stderr.includes("no server running")) {
          throw new Error("tmux server is not running. Start a session first with tmux_create_session.");
        }
        if (stderr.includes("session not found")) {
          throw new Error("Session not found. Use tmux_list_sessions to see available sessions.");
        }
        if (stderr.includes("window not found")) {
          throw new Error("Window not found. Use tmux_list_windows to see available windows.");
        }
        if (stderr.includes("can't find pane")) {
          throw new Error("Pane not found. Use tmux_list_panes to see available panes.");
        }
        throw new Error(`tmux error: ${stderr}`);
      }
      throw error;
    }
  }