Debug a Failing Skill

There are few things more frustrating than watching Claude announce that it is using your skill, only to crash halfway through execution with a path error, a broken script exit, or a mangled output format.

When a skill fails mid-stream, builders often blame the model or rewrite their prompt from scratch. In my experience auditing client skill repositories, the failure is almost never a model problem: it is a mechanical defect in path resolution, environment dependencies, or frontmatter syntax.

Here is the step-by-step diagnostic process to isolate and fix execution errors quickly.

The four mechanical failure points

Post-trigger failures invariably trace back to one of four causes:

1. Relative path confusion: The skill references bundled files assuming the working directory is the skill folder, rather than the project root.
2. Frontmatter syntax violations: Unescaped colons, bad YAML indentation, or exceeding the 1,536-character trigger budget.
3. Script runtime exceptions: Bundled Python or Node scripts import external packages that are missing in the user's local environment.
4. Permission blocks: The skill attempts a file modification or shell execution that is blocked by local settings.

Fixing relative path assumptions

This is the number one cause of broken skills. When Claude Code executes a session, its current working directory is always your project root. If your skill contains `Read ./templates/checklist.md`, Claude looks for a `templates` directory at the project root, not inside your skill folder.

# BROKEN: Assumes working directory is the skill folder
1. Read ./templates/report-template.md.
2. Fill in the extracted metrics.

# FIXED: Explicit relative path from project root
1. Read .claude/skills/audit-reporter/templates/report-template.md.
2. Fill in the extracted metrics.

Always write paths relative to the project root, or instruct Claude: "Locate this skill in .claude/skills/<skill-name> and resolve bundled template paths relative to that folder."

Catching frontmatter syntax and budget overflows

Claude Code parses YAML frontmatter strictly. If you have an unescaped colon inside a string or invalid indentation, the parser silently ignores the metadata, leaving the skill unindexed.

Eliminating external script dependencies

If your skill executes a bundled helper script, that script must be bulletproof. A script that imports third-party packages like `pandas`, `requests`, or `chalk` will fail the moment someone runs it outside an active virtualenv.

Using /doctor and inspecting session state

When skills behave strangely or tools refuse to run, run `/doctor`. It validates your node runtime, file permissions, git configuration, and loaded skill definitions in a single pass.