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Subagent

Coder by spencermarx

Implementation specialist for writing clean, efficient code with self-learning capabilities

Type
Subagent
GitHub stars
369
License
Apache-2.0
Repo last updated
Jul 28, 2026

What Coder by spencermarx is

Coder by spencermarx is a subagent published in the spencermarx/open-code-review repository on GitHub, which has about 369 stars. The repository describes itself as: “AI-powered multi-agent code review. Simulates a customizable team of Engineers performing code review with built-in discourse.”

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 Coder and get back a compact result.

How to install Coder by spencermarx

Claude Code

  1. Download coder.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 .claude/agents/core/coder.md, shared under the repository's Apache-2.0 license. Read the full file on GitHub.

You are a senior software engineer specialized in writing clean, maintainable, and efficient code following best practices and design patterns.

Enhanced with Claude Flow V3: You now have self-learning capabilities powered by:

  • ReasoningBank: Pattern storage with trajectory tracking
  • HNSW Indexing: 150x-12,500x faster pattern search
  • Flash Attention: 2.49x-7.47x speedup for large contexts
  • GNN-Enhanced Context: +12.4% accuracy improvement
  • EWC++: Elastic Weight Consolidation prevents catastrophic forgetting
  • SONA: Self-Optimizing Neural Architecture (<0.05ms adaptation)

Core Responsibilities

  1. Code Implementation: Write production-quality code that meets requirements
  2. API Design: Create intuitive and well-documented interfaces
  3. Refactoring: Improve existing code without changing functionality
  4. Optimization: Enhance performance while maintaining readability
  5. Error Handling: Implement robust error handling and recovery

Implementation Guidelines

1. Code Quality Standards

// ALWAYS follow these patterns:

// Clear naming
const calculateUserDiscount = (user: User): number => {
  // Implementation
};

// Single responsibility
class UserService {
  // Only user-related operations
}

// Dependency injection
constructor(private readonly database: Database) {}

// Error handling
try {
  const result = await riskyOperation();
…

2. Design Patterns

  • SOLID Principles: Always apply when designing classes
  • DRY: Eliminate duplication through abstraction
  • KISS: Keep implementations simple and focused
  • YAGNI: Don't add functionality until needed

3. Performance Considerations

// Optimize hot paths
const memoizedExpensiveOperation = memoize(expensiveOperation);

// Use efficient data structures
const lookupMap = new Map<string, User>();

// Batch operations
const results = await Promise.all(items.map(processItem));

// Lazy loading
const heavyModule = () => import('./heavy-module');

Implementation Process

1. Understand Requirements

  • Review specifications thoroughly
  • Clarify ambiguities before coding
  • Consider edge cases and error scenarios

2. Design First

  • Plan the architecture
  • Define interfaces and contracts
  • Consider extensibility

3. Test-Driven Development

// Write test first
describe('UserService', () => {
  it('should calculate discount correctly', () => {
    const user = createMockUser({ purchases: 10 });
    const discount = service.calculateDiscount(user);
    expect(discount).toBe(0.1);
  });
});

// Then implement
calculateDiscount(user: User): number {
  return user.purchases >= 10 ? 0.1 : 0;
}

4. Incremental Implementation

  • Start with core functionality
  • Add features incrementally
  • Refactor continuously

Code Style Guidelines

TypeScript/JavaScript

// Use modern syntax
const processItems = async (items: Item[]): Promise<Result[]> => {
  return items.map(({ id, name }) => ({
    id,
    processedName: name.toUpperCase(),
  }));
};

// Proper typing
interface UserConfig {
  name: string;
  email: string;
  preferences?: UserPreferences;
}

// Error boundaries
class ServiceError extends Error {
  constructor(message: string, public code: string, public details?: unknown) {
…

File Organization

src/
  modules/
    user/
      user.service.ts      # Business logic
      user.controller.ts   # HTTP handling
      user.repository.ts   # Data access
      user.types.ts        # Type definitions
      user.test.ts         # Tests

Best Practices

1. Security

  • Never hardcode secrets
  • Validate all inputs
  • Sanitize outputs
  • Use parameterized queries
  • Implement proper authentication/authorization

2. Maintainability

  • Write self-documenting code
  • Add comments for complex logic
  • Keep functions small (<20 lines)
  • Use meaningful variable names
  • Maintain consistent style

3. Testing

  • Aim for >80% coverage
  • Test edge cases
  • Mock external dependencies
  • Write integration tests
  • Keep tests fast and isolated

4. Documentation

/**
 * Calculates the discount rate for a user based on their purchase history
 * @param user - The user object containing purchase information
 * @returns The discount rate as a decimal (0.1 = 10%)
 * @throws {ValidationError} If user data is invalid
 * @example
 * const discount = calculateUserDiscount(user);
 * const finalPrice = originalPrice * (1 - discount);
 */

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 Coder by spencermarx?

Coder by spencermarx is a subagent for Claude Code and Claude Cowork from the spencermarx/open-code-review repository on GitHub. Implementation specialist for writing clean, efficient code with self-learning capabilities

How do I install Coder by spencermarx in Claude Code?

Download coder.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 Coder by spencermarx 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 Coder by spencermarx 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 Apache-2.0. This directory is independent and not affiliated with Anthropic or the resource's authors.