How the Claude Code Error Diagnostic Works
The Claude Code Error Diagnostic uses pattern matching against a database of 50+ real-world error messages encountered by Claude Code users. When you paste an error message, the tool runs it against every known error pattern, scores each match, and returns the top 3 most relevant results ranked by confidence.
Each result gives you four things: the exact terminal commands or configuration changes to fix the error right now, a plain-language explanation of why the error occurred in the first place, a prevention rule you can paste into your CLAUDE.md file so it never happens again, and links to detailed guides covering edge cases and advanced troubleshooting.
The diagnostic covers errors from Claude Code's core CLI, the MCP server protocol, API connectivity, file system operations, build toolchains, and environment configuration. Whether you are hitting a stream idle timeout during a long generation or a permission denied when Claude tries to edit files, this tool surfaces the fix in seconds instead of hours of Stack Overflow searching.
The error database is maintained from real support tickets, GitHub issues, and community reports. Patterns are written as regular expressions that match the exact text you see in your terminal, including partial matches and variations across operating systems.
50+ Errors Covered
API & Authentication
API key invalid, rate limits, 429 errors, proxy auth, model not found
Connection & Network
ECONNREFUSED, SSL failures, timeouts, CORS, stream idle timeout
File System & Permissions
EACCES, file not found, disk space, too many open files, chmod issues
MCP & Extensions
Server connection failed, tool not found, skill install failed, hooks
Build & Dev Tools
TypeScript, ESLint, webpack/vite, npm install, Docker, cargo, go mod
Memory & Performance
Heap out of memory, context window exceeded, diff too large, segfault
Git & Version Control
Not initialized, merge conflicts, SSH keys, spawn ENOENT
Configuration
CLAUDE.md not found, invalid JSON settings, env vars, PATH issues
Frequently Asked Questions
Does this tool send my error messages to any server?
No. The entire diagnostic runs in your browser using JavaScript pattern matching. No data is sent anywhere. No API calls are made. Your error messages stay on your machine.
How accurate is the error matching?
The tool uses regex patterns written from real terminal output. It returns the top 3 matches ranked by confidence, so even if the first result is not exactly right, the second or third usually covers your specific variation. Accuracy is highest when you paste the full error message including any stack trace.
What if my error is not in the database?
If none of the 50+ patterns match your error, the tool will tell you no matches were found and suggest checking the
Claude Code Errors Atlas for a comprehensive reference. You can also browse errors by category using the dropdown selector.
Can I use the prevention rules in my CLAUDE.md?
Yes. Every diagnostic result includes a "Prevention rule for CLAUDE.md" section with copy-ready text. Paste it directly into your project's CLAUDE.md file. These rules tell Claude Code to avoid the patterns that trigger the error in the first place.
Why do I get a stream idle timeout?
Stream idle timeouts happen when Claude Code waits too long for the next chunk of a response from the Anthropic API. The default timeout is 120 seconds. Long code generations, complex reasoning, or slow network connections can trigger this. Fix it by setting
ANTHROPIC_TIMEOUT_SECONDS=300 in your environment. See our
full stream idle timeout guide for details.
How do I fix "API key invalid" errors?
First verify your key starts with
sk-ant- and has not expired. Run
echo $ANTHROPIC_API_KEY to check it is set. If it is blank, add
export ANTHROPIC_API_KEY=sk-ant-your-key to your
~/.bashrc or
~/.zshrc and restart your terminal. See our
API key authentication guide.
What is the difference between this tool and the Errors Atlas?
This tool gives you instant, targeted diagnostics: paste an error, get the fix. The
Errors Atlas is a comprehensive reference of every documented error with full context, edge cases, and OS-specific variations. Use the diagnostic for quick fixes, the Atlas for deep dives.
Does this work for MCP server errors?
Yes. The database includes patterns for MCP server connection failures, tool registration errors, skill installation failures, and hook execution problems. These are common when setting up custom MCP servers or configuring Claude Code extensions.
Related Guides
Need More Than Quick Fixes?
This tool covers the basics. For 50 production-ready error fixes with prevention rules and CLAUDE.md configurations, cost optimization templates, and workflow automation guides:
Get the Claude Code Playbook — $99 Lifetime