n8n-io/n8n · error · Error

oldString not found in file: ${filePath}

Error message

oldString not found in file: ${filePath}

What it means

Thrown by edit_file when oldString is not found as a substring of the file content. The file was successfully read and is under the size limit, but the exact text to replace does not exist in the file. This is a string-match failure, not a path or permission issue.

Source

Thrown at packages/@n8n/computer-use/src/tools/filesystem/edit-file.ts:41

			await buildFilesystemResource(dir, filePath, 'filesystemRead', `Read file: ${filePath}`),
			await buildFilesystemResource(dir, filePath, 'filesystemWrite', `Edit file: ${filePath}`),
		];
	},
	async execute({ filePath, oldString, newString }, { dir }) {
		const resolvedReadablePath = await resolveReadablePath(dir, filePath);
		const resolvedWritablePath = await resolveSafePath(dir, filePath);

		const stat = await fs.stat(resolvedReadablePath);
		if (stat.size > MAX_FILE_SIZE) {
			throw new Error(
				`File too large: ${stat.size} bytes (max ${MAX_FILE_SIZE} bytes). Use write_file to replace the entire content.`,
			);
		}

		const content = await fs.readFile(resolvedReadablePath, 'utf-8');

		if (!content.includes(oldString)) {
			throw new Error(`oldString not found in file: ${filePath}`);
		}

		await fs.writeFile(resolvedWritablePath, content.replace(oldString, newString), 'utf-8');

		return formatCallToolResult({ path: filePath });
	},
};

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Read the file first to copy the exact content for oldString
2. Use a shorter, unique substring of the target text as oldString
3. Check for whitespace, tab/space, and line-ending (CRLF/LF) differences
4. Use write_file to replace the entire file if the edit is large or the content is uncertain

Example fix

// before (oldString doesn't match exactly):
await edit_file({ filePath: 'src/app.ts', oldString: 'function main()', newString: 'function main(config)' });

// after (read first, use exact text):
const content = await read_file({ filePath: 'src/app.ts' });
// copy the exact line including whitespace
await edit_file({ filePath: 'src/app.ts', oldString: 'function main() {', newString: 'function main(config) {' });

import * as fs from 'node:fs/promises';

async function validateOldString(filePath: string, oldString: string): Promise<boolean> {
  const content = await fs.readFile(filePath, 'utf-8');
  return content.includes(oldString);
}

// Before calling edit_file:
if (!(await validateOldString(resolvedPath, oldString))) {
  throw new Error('oldString not found. Read the file first to get exact text.');
}

function isOldStringNotFound(e: unknown): boolean {
  return e instanceof Error && e.message.startsWith('oldString not found in file:');
}

When it happens

Trigger: The oldString has different whitespace or indentation than the file, the content was already modified by a prior edit, line endings differ (CRLF vs LF), the oldString was paraphrased rather than copied verbatim, or the target content is in a different file.

Common situations: AI agent generates oldString from memory without reading the file first, or the file changed between read and edit, or tabs vs spaces mismatch.

Related errors

• File too large: ${stat.size} bytes (max ${MAX_FILE_SIZE} byt
• Access denied: "${excludedSegment}" is excluded from filesys
• File too large: ${stat.size} bytes (max ${MAX_FILE_SIZE} byt
• Unsupported binary file — only PNG, JPEG, GIF, WebP and PDF
• Pattern "${pattern}" escapes the base directory

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/6c39b6ffca243a9c. Report an issue: GitHub.