How to Troubleshoot Skill Loading Issues in Anthropic Plugins: A Complete Guide

Troubleshoot skill loading issues in Anthropic plugins by verifying that each skill folder contains a valid SKILL.md file with proper YAML front-matter, removing placeholder text, and repackaging using the package_data_skill.py validator to ensure the .skill zip maintains correct relative paths.

When building extensions for Claude using the anthropics/knowledge-work-plugins repository, skill loading failures can halt development. These errors typically stem from malformed skill manifests, missing metadata, or incorrect packaging of the .skill archive. Understanding the validation pipeline and using the built-in troubleshooting tools will help you resolve these issues quickly.

Understanding the Skill Loading Pipeline

Claude loads skills through a four-stage process defined in the plugin architecture:

• Manifest Discovery: Claude reads .claude-plugin/plugin.json to locate the skills/ directory.
• Skill Scanning: Each subfolder is scanned for a required SKILL.md file containing YAML front-matter with name, description, and version fields.
• Validation: The helper script package_data_skill.py checks for file presence, validates front-matter syntax, and ensures no placeholder text remains.
• Packaging: Skills are compressed into .skill zip files that must preserve the original folder structure for asset path resolution.

Common Skill Loading Errors and Solutions

Missing or Misnamed SKILL.md

Symptom: "Skill could not be loaded" or "Missing SKILL.md".

Fix: Ensure a file named exactly SKILL.md exists at the root of the skill folder. The validator in data/skills/data-context-extractor/scripts/package_data_skill.py explicitly checks for this file before proceeding.

Invalid YAML Front-Matter

Symptom: "SKILL.md missing YAML frontmatter" or validation failures.

Fix: The front-matter must appear at the very top of the file with no leading whitespace or comments:

---
name: Data Context Extractor
description: Extracts contextual metadata from tabular data.
version: 1.0.0
---

Placeholder Text Detection

Symptom: Validation errors mentioning "TODO" or placeholder content.

Fix: Remove all boilerplate strings like "TODO: replace..." before packaging. The validate_skill function scans for leftover template text that indicates incomplete development.

Incorrect Zip Layout

Symptom: Asset path resolution failures or "File not found" errors at runtime.

Fix: The .skill archive must contain files relative to the skill folder root, not nested in an extra directory. The packaging script uses zipfile.ZipFile with ZIP_DEFLATED compression to ensure proper structure.

Step-by-Step Troubleshooting Workflow

1. Locate the skill folder

   $ tree my-plugin/skills/

2. Run the validator

   $ python data/skills/data-context-extractor/scripts/package_data_skill.py /path/to/skill-folder/

   This executes the same validation logic as the Claude runtime, returning specific errors like Missing SKILL.md or Invalid front-matter.

3. Inspect SKILL.md syntax

   Verify the YAML block is exactly at the top with three dashes:

   ---
   name: My Skill
   description: Skill description here.
   version: 1.0.0
   ---

4. Re-package the skill

   $ python data/skills/data-context-extractor/scripts/package_data_skill.py /path/to/skill-folder/

   This creates skill-name.zip in the current directory while maintaining the correct relative paths required by the runtime.

5. Update plugin manifest

   Ensure .claude-plugin/plugin.json references the correct generated zip file.

6. Reload and verify

   Restart the Claude session to confirm the skill loads without errors.

Programmatic Validation and Packaging

Validate skills directly in Python using the same function called by the CLI:

from pathlib import Path
from data.skills.data_context_extractor.scripts.package_data_skill import validate_skill

skill_path = Path("/path/to/skill-folder")
valid, msg = validate_skill(skill_path)
print("✅ Skill OK" if valid else f"❌ {msg}")

Package for distribution with explicit output directory:

$ python data/skills/data-context-extractor/scripts/package_data_skill.py \
    /path/to/skill-folder \
    /tmp/output

The script outputs the path to the generated .skill file, confirming successful packaging.

Summary

• Skill loading requires a SKILL.md file with valid YAML front-matter (name, description, version) at the folder root.
• Validate locally using data/skills/data-context-extractor/scripts/package_data_skill.py to catch errors before deployment.
• Remove placeholders and ensure no "TODO" text remains in the final skill files.
• Package correctly using the provided script to maintain proper zip structure and relative asset paths.
• Sync the manifest in .claude-plugin/plugin.json with the generated .skill file name.

Frequently Asked Questions

Why does Claude report "Missing SKILL.md" when the file exists?

The file must be named exactly SKILL.md (case-sensitive) and located at the root of the skill folder, not in subdirectories. The validator in package_data_skill.py checks for this specific path. Additionally, ensure the file has proper read permissions for the runtime user and that paths do not exceed 255 characters.

What fields are required in the SKILL.md front-matter?

The YAML block must include three mandatory fields: name (the skill identifier), description (human-readable summary), and version (semantic version string). The front-matter must start at line 1 with no preceding whitespace or comments, delimited by --- markers.

How do I fix "Placeholder text detected" errors?

Search your SKILL.md for template strings like "TODO:" or "replace this" and remove them. The validate_skill function explicitly scans for these patterns to ensure developers don't ship unfinished templates. Replace all boilerplate with final content before running the packager.

Can I manually zip the skill folder instead of using the script?

While possible, manual zipping often creates an extra top-level directory that breaks asset path resolution. The package_data_skill.py script uses zipfile.ZipFile with relative path handling to ensure the archive structure matches what Claude expects. Always use the script to avoid layout errors.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}