Conventions check

Code Conventions Checker

Overview

This skill checks code changes against the conventions established in the project's own codebase. Rather than enforcing a fixed ruleset, it discovers conventions by examining the project's configuration files, documentation, and existing code patterns — then validates changes against those conventions.

It works in two modes:

• PR mode: Pass a PR number to analyze all changed files in a pull request
• File mode: Pass file paths or glob patterns to check specific files

Workflow

Step 1: Detect Input Mode and Gather Files

Determine if $ARGUMENTS is a PR number (digits only) or file path(s).

If PR number (digits only):

1. Use Bash to run: gh pr diff <number> --name-only to get the list of changed files
2. Use Bash to run: gh pr diff <number> to get the full diff for context
3. Read each changed file in full using the Read tool

If file path(s) or glob pattern(s):

1. Use Glob to expand any patterns and collect the list of files to check
2. Read each file's contents using the Read tool

Step 2: Discover Project Conventions

Before checking anything, learn what conventions this specific project follows. Read these sources in order of priority (skip any that don't exist):

1. CLAUDE.md (project root) — Often contains explicit architecture, patterns, and coding conventions
2. Linter/formatter configs — Search for and read:
   • .eslintrc, .eslintrc.js, .eslintrc.json, .eslintrc.yml
   • .prettierrc, prettier.config.js
   • checkstyle.xml, .editorconfig
   • tslint.json, biome.json
   • pom.xml (for Java plugin configs like compiler version, encoding)
   • package.json (for eslintConfig, prettier fields, and scripts like lint)
3. Existing code patterns — For each file type being checked, read 2-3 existing files of the same type in the same directory or nearby directories to identify:
   • Naming conventions (classes, methods, files, variables)
   • Import ordering and style
   • Annotation/decorator usage patterns
   • Error handling patterns
   • Test structure and assertion style

Step 3: Internal Consistency Analysis

Before checking against external rules, perform a within-file consistency scan. This catches deviations that no linter config would flag — patterns that are correct in isolation but inconsistent with the rest of the file:

1. Collect all similar constructs — group every instance of: error responses, status codes, variable naming style, string quote style, comment style, and return patterns
2. Identify the dominant pattern — for each group, determine what 80%+ of instances do (e.g., 4 out of 5 error responses use { error: '...' })
3. Flag outliers — any instance that deviates from the dominant pattern is a finding, even if the deviant form is valid on its own

This is critical because inconsistency within a single file is often more confusing to readers than a globally "wrong" but consistent style.

Step 4: Analyze Changes Against Conventions

For each changed/target file, check against the applicable conventions based on file type. Apply discovered rules, filtered by what's actually relevant to this project.

Severity levels:

• Error — Clear violation of an explicit project rule (from CLAUDE.md, linter config, or universal convention)
• Warning — Deviation from the established pattern in surrounding code
• Info — Suggestion based on best practices that the project doesn't explicitly enforce but might benefit from

For each finding, record:

• File (user-friendly relative path)
• Line(s) affected
• Rule violated
• Severity (Error / Warning / Info)
• What was found vs. what was expected
• Suggested fix (one-liner)

Step 5: Generate Report

Present findings in the conversation using this structure:

## Conventions Check Report

**Mode:** PR #<number> / Files: <list>
**Files checked:** <count>
**Findings:** <error-count> errors, <warning-count> warnings, <info-count> info

---

### Summary

| Severity | Count | Categories |
|----------|-------|------------|
| Error    | N     | <which rule categories> |
| Warning  | N     | <which rule categories> |
| Info     | N     | <which rule categories> |

### Findings by File

#### <relative/path/to/file.ext>

| # | Severity | Rule | Line(s) | Finding | Suggestion |
|---|----------|------|---------|---------|------------|
| 1 | Error    | <rule-id> | 42 | <what's wrong> | <how to fix> |
| 2 | Warning  | <rule-id> | 15-18 | <what's wrong> | <how to fix> |

### Conventions Discovered

<Brief list of conventions that were auto-discovered from this project's config and code patterns, so the user can verify the checker's understanding.>

If no findings: Report a clean bill of health with a summary of what was checked.

Important rules for the report:

• Always use relative file paths from the project root
• Include line numbers so developers can navigate directly
• Keep suggestions actionable and specific — "Rename to FooService" not "Follow naming conventions"
• Group findings by file, ordered by severity (errors first)
• Don't report on files that have zero findings (keep the report focused)
• If a convention conflict is found (e.g., CLAUDE.md says one thing but existing code does another), flag it as Info and note the discrepancy