Filesystem MCP

import type {McpServer} from '@modelcontextprotocol/sdk/server/mcp.js'; import {z} from 'zod'; import * as fs from 'node:fs/promises'; import {jsonResult} from '../utils/response.js'; import {expandPath} from '../utils/paths.js'; const description = `Insert text at a specific line in a file. - insert_line = 0: Insert at the beginning - insert_line = N: Insert after line N - insert_text should typically end with a newline - Use absolute paths`; export function registerInsert(server: McpServer): void { server.registerTool( 'insert', { title: 'Insert', description, inputSchema: { path: z.string().describe('Absolute path to file'), insert_line: z.number().int().min(0).describe('Line number to insert after (0 = beginning)'), insert_text: z.string().describe('Text to insert (should end with newline)'), }, annotations: { readOnlyHint: false, destructiveHint: true, }, }, async (args) => { const targetPath = expandPath(args.path); const insertLine = args.insert_line; const insertText = args.insert_text; const content = await fs.readFile(targetPath, 'utf-8'); const lines = content.split('\n'); // Validate line number if (insertLine > lines.length) { throw new Error(`insert_line ${insertLine} is beyond file length (${lines.length} lines)`); } // Warn if insert_text doesn't end with newline let warning: string | undefined; if (!insertText.endsWith('\n')) { warning = 'insert_text does not end with newline - text will run together with next line'; } // Insert the text // Split insert_text into lines (removing trailing newline for array ops) const insertLines = insertText.endsWith('\n') ? insertText.slice(0, -1).split('\n') : insertText.split('\n'); lines.splice(insertLine, 0, ...insertLines); const newContent = lines.join('\n'); await fs.writeFile(targetPath, newContent, 'utf-8'); return jsonResult({ success: true, path: targetPath, insertedAt: insertLine, linesInserted: insertLines.length, ...(warning ? {warning} : {}), }); }, ); }