Skill Prerequisite Check

Scan installed skills, discover their tool/MCP/auth dependencies via heuristic parsing, check if everything is installed and authenticated, and offer to fix issues interactively.

When to Use

• Setting up a new machine
• After installing new skills
• Verifying environment is ready for all skills
• Debugging "tool not found" errors during skill execution

Arguments

Parse from the user's invocation:

• Skill names: Any tokens after the command → filter to those skills only
• Default: scan all skills in ~/.claude/skills/ and .claude/skills/

Workflow

Phase 1: Discover Skills

1. Glob for ~/.claude/skills/*/SKILL.md and .claude/skills/*/SKILL.md
2. Follow symlinks
3. If user specified skill names, filter the list to matching directory names
4. Exclude this skill (skill-prereq-check) from the scan list — its own SKILL.md contains tool references as parsing examples, not actual dependencies
5. Read each SKILL.md file

Phase 2: Parse Prerequisites

For each SKILL.md, extract dependencies using these heuristics:

CLI tools:

• Extract command names (first token of each line) from fenced code blocks marked as bash, shell, or sh
• Also scan ## Prerequisites sections and prose for backtick-quoted tool names followed by "CLI", "installed", or "required"
• Ignore shell builtins and coreutils: echo, cat, ls, mkdir, cd, grep, sed, awk, rm, cp, mv, date, wc, head, tail, sort, uniq, export, set, test, true, false, if, then, else, fi, for, do, done, while, case, esac, command, which, local, return, read, shift, printf, declare
• Ignore git subcommands: the tool is git, not git commit
• Deduplicate per skill

MCP servers:

• Scan for mcp__<server>__ patterns — extract <server> as the MCP server name
• Also scan for <Name> MCP server or <Name> MCP tools in prose — extract <Name> lowercased
• Deduplicate per skill

gh extensions:

• Scan for gh <word> where <word> is NOT a built-in gh command: pr, issue, release, api, auth, repo, project, run, extension, gist, ssh-key, gpg-key, secret, variable, codespace, label, ruleset, cache, attestation, status, browse, search, workflow, config, alias
• Record as gh extension dependency

Auth hints:

• Scan for auth status, auth login, auth test, auth check, authenticated within 200 characters of a tool name
• Mark that tool as needing an auth check

Phase 3: Check Dependencies

Run checks for all discovered dependencies. Use parallel Bash calls where possible. Deduplicate check commands across skills — if multiple skills depend on the same tool, run the check once and reuse the result.

CLI tools:

1. Run command -v <tool> — if exit code 0, installed; otherwise missing
2. If auth hint exists for this tool, run timeout 10 <tool> auth status 2>&1 (or use the Bash tool's timeout parameter set to 10000ms) and check exit code. If exit code != 0, try timeout 10 <tool> auth check 2>&1. If both fail, mark auth as "FAIL". If the command times out, mark auth as "TIMEOUT". If no auth hint, mark as "—"

MCP servers:

1. Use ToolSearch with query +<server> to check if any mcp__<server>__* tools are available in the session
2. If tools found → installed = "yes". If auth tool was referenced in the skill (e.g. auth_test), call it to verify. Otherwise auth = "—"
3. If no tools found → installed = "no", auth = "—"

gh extensions:

1. Run gh extension list once (cache the result)
2. Check if each extension name appears as a suffix in any line of the output (e.g., the line contains /<extension-name> or ends with the extension name)

Phase 4: Present Results

Print a table grouped by skill:

## Prerequisite Check

| # | Skill | Tool | Type | Installed | Auth |
|---|-------|------|------|-----------|------|
| 1 | slack-triage | slack | mcp | yes | yes |
| 2 | meeting-scheduler | gws | cli | yes | FAIL |
| 3 | daily-report | gh | cli | yes | yes |
| 4 | daily-report | slackcli | cli | no | — |
| 5 | oss-release | oss-watch | gh-ext | no | — |

Summary: N skills checked, M tools found, X issues

• "yes" = check passed
• "FAIL" = check ran and failed
• "—" = not applicable (not installed, or no auth pattern detected)
• Number each row for reference in the fix phase

If no issues found, print "All prerequisites satisfied." and stop.

Phase 5: Interactive Fix

If issues exist, ask: "Want me to fix any of these? (e.g. '2, 4' or 'all' or 'done')"

For each selected item, attempt the appropriate fix:

After each fix attempt, re-run the check for that item and show the updated row.

When all selected fixes are attempted, re-print the full table with updated results.

Error Handling

• If ~/.claude/skills/ doesn't exist, report "No skills directory found at ~/.claude/skills/" and check only .claude/skills/
• If a tool's auth check hangs (>10s), kill it and mark as "TIMEOUT"
• If brew is not installed, suggest manual install instructions instead

Examples

Example 1: Check all skills

User: "check prerequisites"
Action: Scan all skills, parse deps, check each, show table

Example 2: Check specific skills

User: "/skill-prereq-check slack-triage meeting-scheduler"
Action: Scan only those two skills, parse deps, check, show table

Example 3: Fix issues

User: (after seeing table) "fix 2, 5"
Action: Run `gws auth login` for item 2, `gh extension install` for item 5, re-check