Universal Quality Gate Skill

Language-agnostic code quality checking system. Automatically detects project languages via marker files and runs appropriate linters, formatters, and static analysis tools for each detected language.

Overview

This skill implements a Detect, Check, Report pattern for multi-language code quality enforcement:

1. Auto-detect languages by scanning for marker files (go.mod, package.json, pyproject.toml, Cargo.toml, etc.)
2. Run language-specific lint, format, type-check, and security tools
3. Report complete results with graceful degradation for unavailable tools

Key Principles:

• Read repository CLAUDE.md files first — Project instructions override default behaviors
• Only run configured tools — Do not add new tools, languages, or checks unless explicitly requested. Keep quality checks focused on what is already defined in language_registry.json.
• Show complete output — Display full linter output, never summarize as "no issues"
• Graceful degradation — Skip unavailable tools without failing the entire gate
• Fail only on required tools — Only return non-zero exit if required tool failures occur

Supported Languages

| Language | Marker Files | Tools | |----------|--------------|-------| | Python | pyproject.toml, requirements.txt | ruff, mypy, bandit | | Go | go.mod | gofmt, golangci-lint, go vet | | JavaScript | package.json | eslint, biome | | TypeScript | tsconfig.json | tsc, eslint, biome | | Rust | Cargo.toml | clippy, cargo fmt | | Ruby | Gemfile | rubocop | | Java | pom.xml, build.gradle | PMD | | Shell | .sh, .bash | shellcheck | | YAML | .yml, .yaml | yamllint | | Markdown | .md | markdownlint |

Instructions

Step 1: Execute Quality Gate

Run the quality gate check against the current project:

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py

This command automatically:

• Detects all languages in the project by scanning for marker files
• Runs language-specific tools for each detected language
• Reports full output with file paths and line numbers
• Returns zero exit code if all required tools pass

Step 2: Choose Your Flow

For pre-commit validation (fastest):

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py --staged

Checks only git-staged files, enabling rapid feedback on recent changes.

For auto-fixing (when issues are found):

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py --fix

Auto-corrects fixable issues (formatting, imports, etc.), then re-run Step 1 to verify.

For focused checking (single language):

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py --lang python

Narrows scope when debugging language-specific issues.

For verbose details:

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py -v

Shows expanded diagnostic output for troubleshooting.

Step 3: Interpret Results

PASSED output:

============================================================
 Quality Gate: PASSED
============================================================

Languages: python, javascript
Files: 15

Tool Results:
  [+] python/lint: passed
  [+] python/format: passed
  [-] python/typecheck: skipped (Optional tool not installed)
  [+] javascript/lint: passed
  [+] javascript/format: passed

Quality gate passed: 4/5 tools OK (1 skipped)

Gate passes when all required tools succeed. Skipped optional tools do not block.

FAILED output:

============================================================
 Quality Gate: FAILED
============================================================

Languages: python, go
Files: 8

Tool Results:
  [X] python/lint: FAILED
      hooks/example.py:42:1: F841 local variable 'x' is assigned but never used
      hooks/example.py:56:1: F401 'os' imported but unused
  [+] python/format: passed
  [+] go/format: passed
  [X] go/lint: FAILED
      main.go:15:2: S1000: should use for range instead of for select

Pattern Matches:
  [WARNING] hooks/example.py:78: Silent exception handler - add explanatory comment

Quality gate failed: 2 tool(s) reported issues, 1 error pattern(s)

Review marked failures X] first. Pattern matches WARNING] are informational.

Step 4: Resolve Issues

For auto-fixable issues:

1. Run python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py --fix
2. Review changes with git diff to verify correctness
3. Re-run Step 1 to confirm all checks pass
4. Commit with message documenting the fixes

For manual fixes:

1. Review each issue line-by-line in the output
2. Edit files to correct the reported problems
3. Re-run Step 1 to verify fixes
4. Commit changes

Step 5: Commit

Once quality gate passes with zero required-tool failures:

1. Run project tests to catch logic regressions
2. Commit with descriptive message
3. Proceed to PR/merge workflow

Common Workflows

Pre-commit validation (fastest path):

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py --staged
# If fails → fix issues → re-run
# If passes → git commit

Full repo audit:

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py
# Review all findings by language
# Fix by category: required failures → warnings → patterns
# Re-run after each batch of fixes

Language-specific validation:

bash
python3 ~/.claude/skills/code-quality/universal-quality-gate/scripts/run_quality_gate.py --lang python
# Use when debugging a specific language's toolchain
# Narrows output and speeds iteration

Extending with New Languages

To add language support without editing the script, modify the language registry:

json
// hooks/lib/language_registry.json
{
  "new_language": {
    "extensions": [".ext"],
    "markers": ["config.file"],
    "tools": {
      "lint": {
        "cmd": "linter {files}",
        "fix_cmd": "linter --fix {files}",
        "description": "Language linter",
        "required": true
      }
    }
  }
}

The quality gate script automatically detects and uses new registry entries on next run.

Error Handling

Error: "No files to check"

Cause: No changed files detected or no language markers found in project Solution:

1. Verify you are in the correct project directory
2. Check that marker files exist (go.mod, package.json, pyproject.toml, etc.)
3. If checking staged files with --staged, ensure files are staged with git add
4. For empty projects, this is expected behavior — add source files first

Error: "Tool not found" / "Required tool not installed"

Cause: A required linter tool is not installed on the system Solution:

1. Identify which tool is missing from the output (e.g., golangci-lint, ruff)
2. Install the tool using your package manager:

• Python: pip install ruff mypy bandit
• Go: go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
• JavaScript: npm install --save-dev eslint biome
• Rust: cargo install clippy (usually pre-installed with rustup)

1. Re-run the quality gate to verify installation
2. Alternative: Mark the tool as optional in language_registry.json if you cannot install it

Error: "Command timed out"

Cause: Tool taking longer than 60-second timeout (usually large file sets or performance issues) Solution:

1. Use --staged to check only changed files instead of the entire project
2. Use --lang to check one language at a time
3. Check for generated files or very large files causing slowdown — add them to .gitignore
4. Verify your system has adequate disk I/O (slow disks can cause timeouts)

Error: "Configuration file conflict"

Cause: Multiple conflicting linter configurations in the project (e.g., .eslintrc and biome.json) Solution:

1. Check which tools the project actually uses (review package.json, go.mod, etc.)
2. Identify the unused tool in language_registry.json
3. Mark it as optional or disable it by removing it from the registry
4. Consult the project's CLAUDE.md for tool preferences — project preferences override defaults
5. Re-run to confirm conflict is resolved

Pattern Match Warnings (not failures)

Pattern Matches like "Silent exception handler" or "Debug print" are informational warnings. They do not fail the gate. Review them and decide whether to fix:

• [WARNING] entries identify failure modes but don't block commits
• Use --no-patterns to skip pattern scanning if these are not relevant
• Manually fix patterns that represent actual problems in your code

Graceful Degradation (Skipped Tools)

When a tool is marked optional and not installed:

• Tool appears as [-] language/tool: skipped (Optional tool not installed)
• Gate still passes because the tool is not required
• If you need that tool's checks, install it and re-run

Architecture

hooks/lib/
  quality_gate.py        # Shared core library
  language_registry.json # Language configurations

skills/code-quality/universal-quality-gate/
  SKILL.md               # This file
  scripts/
    run_quality_gate.py  # Skill entry point (thin wrapper)

This skill uses the shared quality gate library from hooks/lib/ for on-demand code quality checking.

References

Multi-language linting: Language configurations in hooks/lib/language_registry.json

Related skills:

• Use code-linting for single-language lint/format tasks
• Use systematic-code-review for comprehensive code review beyond linting
• Use test-driven-development for full validation with tests

Key principle: Quality gates catch syntax and style issues. They do not replace:

• Unit and integration tests (logic errors, race conditions)
• Code review (architectural problems, API design)
• Domain-specific validation (business logic, performance)