Claude Code Write tool crashes REPL on Windows long-path prefix paths

What this error means

Claude Code REPL crash: TypeError from URL constructor with \\?\ long-path prefix is a Claude Code failure pattern reported for developers trying to fix claude code write tool typeerror long-path prefix windows. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Write tool receives path starting with \?\ (Windows long-path prefix). URL constructor throws TypeError. Unhandled exception crashes the REPL. Occurs in VS Code extension on Windows 11.

Common causes

• Windows developers using extended-length path prefix (\?) for deep directories hit unhandled TypeError crash. Entire REPL session lost. No recovery without restart.
• Write tool receives path starting with \?\ (Windows long-path prefix). URL constructor throws TypeError. Unhandled exception crashes the REPL. Occurs in VS Code extension on Windows 11.

Quick fixes

1. Confirm the exact error signature matches Claude Code REPL crash: TypeError from URL constructor with \\?\ long-path prefix.
2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/anthropics/claude-code/issues/59316

Evidence note: Write tool receives path starting with \?\ (Windows long-path prefix). URL constructor throws TypeError. Unhandled exception crashes the REPL. Occurs in VS Code extension on Windows 11.

Related errors

• Claude Code ENOENT UNC network paths
• Claude Code Cowork Hyper-V Unavailable 0x80070005

FAQ

What should I check first?

Start with the exact Claude Code REPL crash: TypeError from URL constructor with \\?\ long-path prefix text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Claude Code workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without Claude Code REPL crash: TypeError from URL constructor with \\?\ long-path prefix.