Write File
write_fileDestructiveIdempotent
Create or overwrite files with specified content in allowed directories. Handles text encoding and requires caution as existing files are replaced without warning.
Instructions
Create a new file or completely overwrite an existing file with new content. Use with caution as it will overwrite existing files without warning. Handles text content with proper encoding. Only works within allowed directories.
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| path | Yes | ||
| content | Yes |
Output Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| content | Yes |
Implementation Reference
- src/filesystem/index.ts:335-343 (handler)The handler function for the 'write_file' tool. It validates the input path and delegates the actual writing to the writeFileContent helper function.
async (args: z.infer<typeof WriteFileArgsSchema>) => { const validPath = await validatePath(args.path); await writeFileContent(validPath, args.content); const text = `Successfully wrote to ${args.path}`; return { content: [{ type: "text" as const, text }], structuredContent: { content: text } }; } - src/filesystem/index.ts:94-97 (schema)Zod schema defining the input arguments for the write_file tool: path (string) and content (string).
const WriteFileArgsSchema = z.object({ path: z.string(), content: z.string(), }); - src/filesystem/index.ts:320-344 (registration)Registration of the 'write_file' tool using server.registerTool, specifying title, description, schemas, annotations, and handler.
server.registerTool( "write_file", { title: "Write File", description: "Create a new file or completely overwrite an existing file with new content. " + "Use with caution as it will overwrite existing files without warning. " + "Handles text content with proper encoding. Only works within allowed directories.", inputSchema: { path: z.string(), content: z.string() }, outputSchema: { content: z.string() }, annotations: { readOnlyHint: false, idempotentHint: true, destructiveHint: true } }, async (args: z.infer<typeof WriteFileArgsSchema>) => { const validPath = await validatePath(args.path); await writeFileContent(validPath, args.content); const text = `Successfully wrote to ${args.path}`; return { content: [{ type: "text" as const, text }], structuredContent: { content: text } }; } ); - src/filesystem/lib.ts:138-162 (helper)Helper function that implements secure file writing with checks for symlinks and atomic operations to prevent race conditions.
export async function writeFileContent(filePath: string, content: string): Promise<void> { try { // Security: 'wx' flag ensures exclusive creation - fails if file/symlink exists, // preventing writes through pre-existing symlinks await fs.writeFile(filePath, content, { encoding: "utf-8", flag: 'wx' }); } catch (error) { if ((error as NodeJS.ErrnoException).code === 'EEXIST') { // Security: Use atomic rename to prevent race conditions where symlinks // could be created between validation and write. Rename operations // replace the target file atomically and don't follow symlinks. const tempPath = `${filePath}.${randomBytes(16).toString('hex')}.tmp`; try { await fs.writeFile(tempPath, content, 'utf-8'); await fs.rename(tempPath, filePath); } catch (renameError) { try { await fs.unlink(tempPath); } catch {} throw renameError; } } else { throw error; } } }