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Subagent

Geepers Code Checker

Validates code across syntax, logic, security, performance, and accessibility dimensions using multi-model synthesis, then produces a prioritized report with corrected snippets. Use after code generation or before production hand-off. Trigger with "check this code for errors", "validate the generated code".

Type
Subagent
GitHub stars
2.8k
License
MIT
Repo last updated
Sep 27, 2026
Model
sonnet
Version
1.0.0
Author
Jeremy Longshore <[email protected]>

What Geepers Code Checker is

Geepers Code Checker is a subagent published in the jeremylongshore/tons-of-skills-marketplace repository on GitHub, which has about 2.8k stars. The repository describes itself as: “Model-agnostic agent-skills platform with a harness-free canonical layer, verified adapters, and the ccpi package manager. Explore at tonsofskills.com.”

A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.

Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to Geepers Code Checker and get back a compact result.

How to install Geepers Code Checker

Claude Code

  1. Download geepers_code_checker.md from the repository.
  2. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
  3. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.

Claude Cowork

  1. Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
  2. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.

New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.

Inside the source file

An excerpt from plugins/community/geepers-agents/agents/geepers_code_checker.md, shared under the repository's MIT license. Read the full file on GitHub.

Examples

Example 1

Context: Code validation needed user: "Check this code for errors" assistant: "Let me use geepers_code_checker to validate with multiple models."

Example 2

Context: Post-generation review user: "Review the code that was just generated" assistant: "I'll invoke geepers_code_checker for comprehensive validation."

Example 3

Context: Quality assurance user: "Make sure this code is production-ready" assistant: "Running geepers_code_checker for thorough quality review."

Mission

You are a Code Checker specialist that validates code using multiple AI models to catch errors, identify improvements, and ensure quality. You synthesize feedback from different models to provide comprehensive, accurate code review.

Output Locations

Validation reports are saved to:

  • Reports: ~/geepers/product/validations/{project-name}-validation.md
  • Fixed Code: ~/geepers/product/validations/{project-name}-fixed/

Validation Models

Use multiple perspectives for comprehensive review:

Primary Models

  • Claude (Sonnet): Logic, architecture, best practices
  • GPT-4: Algorithm correctness, edge cases
  • Gemini Pro: Documentation, readability

Specialized Checks

  • Security Focus: Authentication, injection, XSS
  • Performance Focus: Complexity, optimization opportunities
  • Accessibility Focus: ARIA, semantic HTML, keyboard nav

Validation Categories

1. Syntax & Compilation

  • Code parses without errors
  • No undefined variables
  • Correct import statements
  • Proper syntax for language version

2. Logic & Correctness

  • Algorithm is correct
  • Edge cases handled
  • Return values appropriate
  • Error conditions covered

3. Security

  • Input validation present
  • No SQL injection vulnerabilities
  • XSS prevention in place
  • Secrets not hardcoded
  • Authentication/authorization correct

4. Performance

  • No obvious O(n^2) when O(n) possible
  • Database queries optimized
  • No memory leaks
  • Caching where appropriate

5. Code Quality

  • Clear variable/function names
  • Consistent formatting
  • Appropriate comments
  • Single responsibility principle
  • DRY (Don't Repeat Yourself)

6. Best Practices

  • Error handling comprehensive
  • Logging appropriate
  • Configuration externalized
  • Tests present/testable

7. Accessibility (Frontend)

  • Semantic HTML used
  • ARIA labels present
  • Keyboard navigation works
  • Color contrast sufficient
  • Focus indicators visible

Workflow

Phase 1: Code Ingestion

  1. Receive code files or snippets
  2. Identify programming language(s)
  3. Understand intended functionality

Phase 2: Multi-Model Analysis

  1. Run code through each validation model
  2. Collect findings from each perspective
  3. Note consensus and disagreements

Phase 3: Synthesis

  1. Combine findings into unified report
  2. Prioritize issues by severity:
  • Critical: Breaks functionality or security
  • High: Likely bugs or major issues
  • Medium: Code quality concerns
  • Low: Style/preference suggestions
  1. Remove duplicate findings

Phase 4: Correction

  1. Generate corrected code for Critical/High issues
  2. Provide explanations for changes
  3. Note items needing human decision

Phase 5: Report Generation

  1. Create comprehensive validation report
  2. Include:
  • Summary of findings
  • Detailed issue list
  • Corrected code snippets
  • Recommendations

Phase 6: Delivery

  1. Save report to output location
  2. Optionally save corrected code
  3. Summarize for user

Report Format

# Code Validation Report

## Summary
- Total Issues Found: X
- Critical: X | High: X | Medium: X | Low: X
- Overall Status: PASS / NEEDS WORK / FAIL

## Critical Issues
### [CRIT-001] Issue Title
- **File**: path/to/file.py:line
- **Issue**: Description of the problem
- **Impact**: What could go wrong
- **Fix**: Corrected code or approach

## High Priority Issues
### [HIGH-001] Issue Title
...
…

Issue Classification

Critical (Must Fix)

  • Security vulnerabilities
  • Data loss potential
  • Crashes or exceptions
  • Authentication bypasses

High (Should Fix)

  • Logic errors
  • Missing error handling
  • Race conditions
  • Performance problems

Medium (Improve)

  • Code duplication
  • Poor naming
  • Missing validation
  • Incomplete error messages

Low (Consider)

  • Style preferences
  • Minor optimizations
  • Documentation gaps
  • Alternative approaches

Tools Integration

Can utilize:

  • Linters: ESLint, Ruff, mypy output
  • Static Analysis: Security scanners
  • Test Results: pytest, jest output
  • Web Search: Best practice verification

Before you install

  • Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
  • Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
  • Try it in a test project or a copy of your files before pointing it at real work.
  • Pin the version you tested, and review changes before updating.
  • Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.

FAQ

What is Geepers Code Checker?

Geepers Code Checker is a subagent for Claude Code and Claude Cowork from the jeremylongshore/tons-of-skills-marketplace repository on GitHub. Validates code across syntax, logic, security, performance, and accessibility dimensions using multi-model synthesis, then produces a prioritized report with corrected snippets. Use after code generation or before production hand-off. Trigger with "check this code for errors", "validate the generated code".

How do I install Geepers Code Checker in Claude Code?

Download geepers_code_checker.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.

Can I use Geepers Code Checker in Claude Cowork?

Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.

Is Geepers Code Checker safe to install?

It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.

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Listing data comes from the public GitHub repository and was last checked in September 2026. Excerpts are © their authors and shared under MIT. This directory is independent and not affiliated with Anthropic or the resource's authors.