[BUG] Skills System References Non-Existent file_read Tool

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Summary

The Claude Desktop skills system contains a configuration error that references a non-existent file_read tool, causing skills to fail when attempting to read their own SKILL.md and reference files.

Problem Description

When a skill is invoked in Claude Desktop, the <additional_skills_reminder> section instructs:

please begin the response to each and every request in which computer use is implicated
by using the file_read tool to read the appropriate SKILL.md files

However, there is no file_read tool available to skills.

What Happens

1. Skill receives instruction to use file_read tool
2. Skill searches available tools, finds no file_read
3. Skill guesses and attempts filesystem:read_text_file as closest match
4. This fails because:

• Skills run in containers with files mounted at /mnt/skills/<skill-name>/
• filesystem:* tools are restricted to user directories (e.g., /Users/)
• filesystem:* tools cannot access /mnt/skills/ paths

1. Skill cannot read its own SKILL.md → goes off course or fails

Available Tools for Skills

According to the error trace, skills have access to:

• filesystem:read_text_file (doesn't work for /mnt/skills/)
• filesystem:read_file (deprecated, doesn't work for /mnt/skills/)
• bash_tool ✅ (works for /mnt/skills/)
• view ✅ (works for /mnt/skills/)

What Should Happen?

Correct Fix

The <additional_skills_reminder> instruction should be updated to use tools that actually work for skill containers:

Option 1 - Use bash_tool:
please begin the response to each and every request in which computer use is implicated
by using the bash_tool to cat the appropriate SKILL.md files from /mnt/skills/<skill-name>/

Option 2 - Use view tool:
please begin the response to each and every request in which computer use is implicated
by using the view tool to read the appropriate SKILL.md files from /mnt/skills/<skill-name>/

Impact

• Skills cannot reliably access their own instruction files
• Skills fail or behave incorrectly when they need to reference SKILL.md
• Degrades skill functionality and user experience

Environment

• Claude Desktop (with skills support)
• Skill system version: Current production
• Location of bug: System-level skill configuration (<additional_skills_reminder>)

Error Messages/Logs

Good question - let me trace back exactly why I tried `filesystem:read_text_file`:

Looking at my instructions, in the `<additional_skills_reminder>` section, it says:


please begin the response to each and every request in which computer use is implicated by using the `file_read` tool to read the appropriate SKILL.md files


But here's the issue: **there is no `file_read` tool available to me.** Looking at my available functions, I have:

- `filesystem:read_text_file`
- `filesystem:read_file` (deprecated)
- `bash_tool`
- `view`

So when the instructions said "use the `file_read` tool", I interpreted that as `filesystem:read_text_file` since that's the closest match in my available tools.

**The programmatic error is:** The instructions reference a `file_read` tool that doesn't exist in my function list. This caused me to guess at which tool was meant, and I guessed wrong.

**What the instructions should probably say instead:**
- Use `bash_tool` to cat the SKILL.md file, OR
- Use `view` tool to read the SKILL.md file

Both of those tools work for files in `/mnt/skills/`, whereas the `filesystem:` tools are restricted to `/Users/jaytarzwell`.

So yes, this looks like it could be a documentation mismatch in the skill system instructions that you might want to correct.

Steps to Reproduce

Reproduction

1. Create any skill with SKILL.md
2. Invoke the skill in Claude Desktop with a task requiring computer use
3. Observe skill attempting filesystem:read_text_file and failing
4. Check logs for references to non-existent file_read tool

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.0.24 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

When the skill is called it looks for a system tool you haven't provisioned it with. It does eventually find what it has to do but that takes user interventions.