Fix Claude Code Edit/Write File Modification Errors

Dealing with software glitches can be a real buzzkill, especially when you're in the zone, trying to code or make those crucial edits. One such frustrating issue that users of Claude Code have encountered is an persistent error loop: "File has been unexpectedly modified. Read it again before attempting to write it." This error, particularly when using the Edit/Write tools, can halt your workflow in its tracks, leaving you scratching your head. You've just read the file, you know no external programs are interfering, and yet, Claude Code insists the file has changed out from under it. It’s a baffling predicament that can make even the simplest file manipulation feel like an insurmountable challenge. But don't despair! This article is here to guide you through understanding this peculiar bug, its potential causes, and, most importantly, how to overcome it, ensuring your Claude Code experience remains productive and smooth.

We'll dive deep into the mechanics of this error, exploring why it might be happening even when you're confident nothing else is touching your files. From potential timing issues to how the system perceives file integrity, we'll unpack the possibilities. Understanding the root cause is the first step toward a lasting solution. We’ll also look at the practical steps you can take to break out of this loop, including effective workarounds that have helped other users get back to their coding tasks without further interruption. By the end of this guide, you’ll be equipped with the knowledge and strategies to tackle the "File has been unexpectedly modified" error head-on and ensure that Claude Code’s powerful editing capabilities are at your full disposal, without these annoying hiccups. So, let’s get started on reclaiming your coding flow and making file edits a breeze once again!

Understanding the "File Has Been Unexpectedly Modified" Error in Claude Code

The "File has been unexpectedly modified" error in Claude Code is a perplexing issue that arises when the tool attempts to write changes to a file but detects a discrepancy between the version it's holding in memory and the version currently on disk. This error message, "File has been unexpectedly modified. Read it again before attempting to write it," is essentially Claude Code's way of saying, "Hey, I think something changed this file since I last looked at it, and I can't guarantee my changes will be applied correctly if I just overwrite whatever is there now." This is a safety mechanism designed to prevent data corruption. However, the frustration stems from the fact that, in many reported cases, no external modifications are actually occurring. The file might have just been read successfully moments before, and no other applications or processes are actively altering it. This leads to a seemingly illogical loop: Claude Code reads the file, tries to write, gets the error, reads the file again (sometimes reporting a different line count, sometimes not), and then attempts to write again, repeating the cycle.

This particular bug has been observed in specific versions of Claude Code, notably impacting users on Windows utilizing the Windows Subsystem for Linux (WSL). The context of file operations within this environment, especially when dealing with file types like .shader files within Unity projects, seems to exacerbate the problem. The core of the issue often lies in how Claude Code, or the underlying system, handles file timestamps and content validation. When Claude Code reads a file, it likely stores a snapshot of its content or a hash of it. Before writing, it re-checks the file's status. If, during the brief interval between reading and writing, the file's modification timestamp changes, or if the content is perceived to have diverged (even subtly), the error is triggered. This could be due to background processes within the operating system, antivirus software scanning the file, or even subtle timing differences in how WSL interacts with the Windows file system.

It’s important to differentiate this from genuine file modifications. In a typical scenario, if a file is genuinely modified by another program while Claude Code is preparing to write, the error is valid and necessary. The problem arises when this error occurs despite all evidence pointing to the contrary – when the file should be exactly as Claude Code last saw it. This points towards a potential bug in the file monitoring or comparison logic within Claude Code itself, or an interaction issue with the specific operating system and file system configuration. The loop suggests that even after re-reading the file, the subsequent write operation still fails the integrity check, potentially because the check itself is too sensitive or misinterpreting data.

Delving Deeper: Why Does This Loop Happen?

The recurring "File has been unexpectedly modified" loop in Claude Code, particularly noted when using the Edit/Write tools on Windows with WSL, is a complex issue that often boils down to a few critical factors. At its heart, the tool employs a safeguard mechanism: before writing any changes, it verifies that the file on disk hasn't been altered since it was initially read. This is a standard and necessary procedure to prevent accidental data overwrites and maintain file integrity. The problem arises when this verification process triggers erroneously, leading to the continuous error loop. One of the primary culprits can be timing sensitivity and file system monitoring. When Claude Code reads a file, it creates an internal representation or a checksum of that file’s state. Between the moment of reading and the moment of writing, even a fraction of a second can be enough for certain system processes to interact with the file. This could include:

• Antivirus Software: Real-time scanning by antivirus programs can momentarily lock or modify file metadata, including timestamps, as they check for threats. This brief interaction can be enough to make Claude Code believe the file has been changed.
• Operating System Background Tasks: Windows, especially with WSL integration, has numerous background services that manage file indexing, caching, and synchronization. Some of these might perform quick checks or updates on files that are accessed, inadvertently altering their state in a way that trips Claude Code’s error detection.
• IDE or Editor Integration: Even if you don't have the file open in a separate editor, your IDE (like Unity, in this context) might have background processes that monitor project files for changes. Unity, for example, often recompiles or re-imports assets when files are modified, and its internal file watchers could be the source of the perceived modification.

Another significant factor could be how timestamps and file metadata are handled across different file systems, especially between Windows and WSL. WSL mounts Windows drives, and the way file system events and metadata (like modification times) are translated between these environments might not always be perfectly synchronized. A change that appears instantaneous and insignificant in one system could be registered differently in the other, leading to a mismatch detected by Claude Code.

Furthermore, potential bugs within Claude Code's file comparison logic itself cannot be ruled out. The tool might be overly sensitive to minute changes in file content or metadata that are not truly indicative of an external modification. For instance, a slight difference in line endings, a change in file encoding that is later reverted, or even how the tool reads and writes internal buffers could lead to a perceived modification. The log snippets provided show Claude Code attempting to re-read the file and even resorting to bash commands like cat and sleep, indicating it's actively trying to reconcile the situation but failing to bypass the error condition. The Korean messages in the logs also suggest the tool is aware of potential external modifications and is attempting to adapt, but the core issue persists.

Finally, session-specific issues or state corruption within Claude Code could also be at play. Sometimes, software can enter an unexpected state that causes it to misinterpret file operations. This is often why a simple restart of Claude Code can temporarily resolve the issue, as it resets the tool's internal state. Understanding these underlying mechanisms is crucial for diagnosing and ultimately resolving the persistent loop.

Navigating the Error: Step-by-Step Solutions and Workarounds

Encountering the "File has been unexpectedly modified" error loop in Claude Code can be a significant roadblock. Fortunately, there are several strategies you can employ to break free from this cycle and get back to your work. While a permanent fix often relies on updates to the software itself, these workarounds are effective for immediate relief and continued productivity.

1. The Immediate Fix: Restarting Claude Code

As noted in the additional information, the most straightforward and often effective solution is to restart Claude Code. This is because the error can sometimes be caused by an internal state corruption within the application. When you restart the tool, you reset its memory and processes, clearing any erroneous flags or data that might be causing the false modification detection. This is usually a temporary fix, meaning the error might reappear later, but it’s the quickest way to get unstuck.

2. Verifying File Integrity and External Influences

Before resorting to restarts, take a moment to manually verify that no other process is actually modifying the file. While you might be confident, it's worth double-checking:

• Close the file in all editors and IDEs: Ensure that your main development environment (like Unity) or any other text editors are not actively holding the file open.
• Check for background sync services: If you use cloud storage services (like Dropbox, OneDrive, Google Drive) that sync your project folder, temporarily disable their real-time syncing for that specific folder or pause syncing altogether while you work with Claude Code.
• Temporarily disable antivirus scanning: As mentioned, antivirus software can interfere. You can try briefly disabling real-time scanning for the specific file or directory Claude Code is accessing. Remember to re-enable it afterward for security.

3. Leveraging the "Write to New File" Approach

If direct editing is consistently failing, Claude Code offers a fallback: writing to a new file. This is a multi-step workaround:

1. Ask Claude Code to read the file. Wait for it to confirm it has read the content.
2. Instruct Claude Code to create a new file (e.g., DS_SpriteLit_new.shader) and write the modified content there.
3. Once Claude Code confirms the new file has been written successfully, you can then manually copy the content from the newly created file and paste it into the original file. Alternatively, you might be able to use your operating system's commands (like cp in WSL or move in Windows cmd) to replace the original file with the new one, but be cautious with this approach.

This method bypasses the direct overwrite conflict by creating a separate, new file, which often avoids triggering the