Windows: Hook system missing TOOL_NAME and EXIT_CODE environment variables

Issue Summary

The Claude Code hook system on Windows (VSCode extension) does not set the TOOL_NAME and EXIT_CODE environment variables that are essential for implementing useful PreToolUse and PostToolUse hooks. This makes it impossible to log which tools are being executed and whether they succeed or fail.

Environment

• Platform: Windows 10 Pro
• Claude Code Version: VSCode extension
• Entry Point: claude-vscode (from CLAUDE_CODE_ENTRYPOINT env var)
• SDK Version: 0.1.75 (from CLAUDE_AGENT_SDK_VERSION env var)
• Shell: Git Bash (MINGW64)

Expected Behavior

According to the Claude Code hook system design:

1. PreToolUse hooks should have access to:

• TOOL_NAME environment variable containing the name of the tool about to be executed

1. PostToolUse hooks should have access to:

• TOOL_NAME environment variable containing the name of the tool that was executed
• EXIT_CODE environment variable containing the exit code (0 for success, non-zero for failure)

This allows implementing logging and debugging workflows like:

[14:23:15] PRE: Bash
[14:23:15] POST: Bash (exit: 0) ✓
[14:23:16] PRE: Read
[14:23:16] POST: Read (exit: 0) ✓

Actual Behavior

On Windows:

• ✅ Hooks DO execute successfully
• ❌ TOOL_NAME environment variable is NOT set
• ❌ EXIT_CODE environment variable is NOT set

This results in hooks having no context about what tool was executed or whether it succeeded, making the hook system essentially useless for debugging and logging purposes.

Steps to Reproduce

1. Configure Hooks

Add to ~/.claude/settings.json:

{
  "hooks": {
    "PreToolUse": [{
      "matcher": ".*",
      "hooks": [{
        "type": "command",
        "command": "powershell -Command \"Add-Content -Path 'C:\\Users\\Luke\\.claude\\debug.log' -Value 'PRE: %TOOL_NAME%'\""
      }]
    }],
    "PostToolUse": [{
      "matcher": ".*",
      "hooks": [{
        "type": "command",
        "command": "powershell -Command \"Add-Content -Path 'C:\\Users\\Luke\\.claude\\debug.log' -Value 'POST: %TOOL_NAME% (exit: %EXIT_CODE%)'\""
      }]
    }]
  }
}

2. Execute Any Tool

Run any Claude Code command (e.g., ls, echo "test")

3. Check Log Output

Expected:

PRE: Bash
POST: Bash (exit: 0)

Actual:

PRE:
POST:  (exit: )

The variables are empty/not set.

Evidence

Testing Iterations

We exhaustively tested multiple approaches to rule out configuration errors:

1. ✅ Bash commands - Hooks executed, but path resolution failed on Windows
2. ✅ PowerShell with various quote escaping - Hooks executed, variables empty
3. ✅ PowerShell script files - Hooks executed, variables empty
4. ✅ Windows batch files - Hooks executed, variables empty
5. ✅ Full environment dump - Confirmed variables don't exist

Environment Variables That ARE Available

When we dumped ALL environment variables from inside a hook, we found these Claude-specific variables:

CLAUDE_AGENT_SDK_VERSION=0.1.75
CLAUDE_CODE_ENABLE_SDK_FILE_CHECKPOINTING=true
CLAUDE_CODE_ENTRYPOINT=claude-vscode
CLAUDE_PROJECT_DIR=c:\Users\Luke\Documents\Claude Code\hq

Environment Variables That Are MISSING

TOOL_NAME=<not set>
EXIT_CODE=<not set>

We checked for multiple variations:

• TOOL_NAME, ToolName, CLAUDE_TOOL_NAME - None exist
• EXIT_CODE, ExitCode, CLAUDE_EXIT_CODE - None exist

Example Log Output

From our testing session:

[23:48:26] PRE:
[23:48:27] POST:  (exit: ) ERROR
[23:48:34] PRE:
[23:48:35] POST:  (exit: ) ERROR

The hooks execute (timestamps appear), but the variable placeholders are empty.

Impact

Current State

• Cannot implement debugging workflows on Windows
• Cannot log tool execution for troubleshooting
• Cannot track success/failure of tool executions
• Platform disparity if this works on Linux/macOS (unconfirmed)

Use Cases Blocked

• Debugging Claude Code behavior by logging all tool calls
• Tracking tool failures for error analysis
• Building execution metrics
• Creating custom error recovery workflows
• Self-correction based on execution history

Workaround Status

None available. The environment variables simply don't exist.

Questions

1. Is this expected behavior?

• Should these variables be set on Windows?
• Is there a platform-specific limitation?

1. Does this work on Linux/macOS?

• If yes, this is a Windows-specific bug
• If no, this might be a documentation gap

1. Is there an alternative approach?

• Are there other environment variables we should use?
• Is there a different hook mechanism for Windows?

Suggested Fix

If this is a bug, the Windows version should set these environment variables when executing hooks:

PreToolUse:

TOOL_NAME=<name of tool about to execute>

PostToolUse:

TOOL_NAME=<name of tool that executed>
EXIT_CODE=<exit code: 0 for success, non-zero for error>

This would bring Windows hook functionality to parity with the documented behavior and enable powerful debugging/logging workflows.

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Summary: Hooks execute on Windows but lack the TOOL_NAME and EXIT_CODE environment variables needed for useful logging/debugging workflows. Request confirmation if this is expected behavior or a platform-specific bug that needs fixing.