RxJS MCP Server

日本語版 README はこちら

⚠️ This is an unofficial community project, not affiliated with RxJS team.

Execute, debug, and visualize RxJS streams directly from AI assistants like Claude.

Features

🚀 Stream Execution

• Execute RxJS code and capture emissions

• Timeline visualization with timestamps

• Memory usage tracking

• Support for all major RxJS operators

📊 Marble Diagrams

• Generate ASCII marble diagrams

• Visualize stream behavior over time

• Automatic pattern detection

• Clear legend and explanations

🔍 Operator Analysis

• Analyze operator chains for performance

• Detect potential issues and bottlenecks

• Suggest alternative approaches

• Categorize operators by function

🛡️ Memory Leak Detection

• Identify unsubscribed subscriptions

• Detect missing cleanup patterns

• Framework-specific recommendations (Angular, React, Vue)

• Provide proper cleanup examples

💡 Pattern Suggestions

• Get battle-tested RxJS patterns

• Framework-specific implementations

• Common use cases covered:

  • HTTP retry with backoff

  • Search typeahead

  • WebSocket reconnection

  • Form validation

  • State management

  • And more...

Related MCP server: NestJS DevTools MCP

Installation

Requirements

• Node.js >= 22 (engines.node). The MCP TypeScript SDK v2 this server is built on requires Node.js >= 20; this package sets the higher floor to stay on a maintained LTS line.

# Install globally
npm install -g @shuji-bonji/rxjs-mcp

# Or use with npx
npx @shuji-bonji/rxjs-mcp

Configuration

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "rxjs": {
      "command": "npx",
      "args": ["@shuji-bonji/rxjs-mcp"]
    }
  }
}

VS Code with Continue/Copilot

Add to .vscode/mcp.json:

{
  "mcpServers": {
    "rxjs": {
      "command": "npx",
      "args": ["@shuji-bonji/rxjs-mcp"]
    }
  }
}

Cursor

Add to ~/.cursor/mcp.json:

{
  "mcpServers": {
    "rxjs": {
      "command": "npx",
      "args": ["@shuji-bonji/rxjs-mcp"]
    }
  }
}

Available Tools

execute_stream

Execute RxJS code and capture stream emissions with timeline.

The tool accepts either an expression that evaluates to an Observable, or a snippet ending in such an expression — return is optional.

// ✅ Trailing expression (v0.2.0+): the last expression is returned implicitly
interval(100).pipe(
  take(5),
  map((x) => x * 2),
);

// ✅ Declaration + trailing reference
const stream$ = interval(100).pipe(
  take(5),
  map((x) => x * 2),
);
stream$;

// ✅ Explicit return (always works)
return interval(100).pipe(
  take(5),
  map((x) => x * 2),
);

generate_marble

Generate ASCII marble diagrams from event data.

// Input: array of timed events
[
  { time: 0, value: 'A' },
  { time: 50, value: 'B' },
  { time: 100, value: 'C' },
];

// Output: A----B----C--|

analyze_operators

Analyze RxJS operator chains for performance and best practices.

// Analyzes chains like:
source$.pipe(
  map((x) => x * 2),
  filter((x) => x > 10),
  switchMap((x) => fetchData(x)),
  retry(3),
);

detect_memory_leak

Detect potential memory leaks and missing cleanup.

// Detects issues like:
- Missing unsubscribe
- No takeUntil operator
- Uncompleted Subjects
- Infinite intervals

suggest_pattern

Get production-ready patterns for common use cases.

Available patterns:

• http-retry - Resilient HTTP with retry

• search-typeahead - Debounced search

• polling - Smart polling with backoff

• websocket-reconnect - Auto-reconnecting WebSocket

• form-validation - Reactive form validation

• state-management - Simple state store

• cache-refresh - Cache with refresh strategy

• And more...

lint_rxjs

Lint RxJS code snippets for common issues and best practices. Based on eslint-plugin-rxjs-x rules.

// Parameters:
{
  code: string;           // RxJS code to lint
  config?: 'recommended' | 'strict';  // Rule set (default: recommended)
  framework?: 'angular' | 'react' | 'vue' | 'none'; // Framework context
  rules?: string[];       // Specific rules to check (overrides config)
}

Config levels:

• recommended — 20 rules covering the most common issues

• strict — the 28 rules in eslint-plugin-rxjs-x's strict (no-exposed-subjects, no-misused-observables, no-unnecessary-collection, etc.)

finnish is in neither config, matching the plugin, and runs only when named: rules: ["finnish"]. Framework-specific checks are added on top of both levels.

Framework-specific checks:

• Angular — Detects missing takeUntilDestroyed() or takeUntil(destroy$) in components

• React — Detects subscribe() without useEffect cleanup

• Vue — Detects subscribe() without onUnmounted cleanup

Usage Examples

With Claude

User: "Execute this RxJS stream and show me the output"

Claude: I'll execute that RxJS stream for you.

[Uses execute_stream tool]

## Stream Execution Result
✅ Completed
Execution Time: 523ms
Values Emitted: 5

### Emitted Values
[0, 2, 4, 6, 8]

Debugging Memory Leaks

User: "Check this Angular component for memory leaks"

Claude: I'll analyze your component for potential memory leaks.

[Uses detect_memory_leak tool]

## Memory Leak Analysis
⚠️ Potential leaks detected

1. 🔴 subscription (high severity)
   - Found 3 subscribe() calls but only 1 unsubscribe()
   - Fix: Use takeUntil pattern with destroy$ subject

Getting Patterns

User: "Show me how to implement search with RxJS"

Claude: I'll show you the search typeahead pattern.

[Uses suggest_pattern tool with useCase: 'search-typeahead']

## Search Typeahead with Debounce
[Full implementation with explanation]

Security

The execute_stream tool runs user-provided code in an isolated Worker thread to prevent:

• Main process pollution

• Resource leaks from infinite loops or timers

• Access to sensitive Node.js APIs (process, fs, etc.)

Execution is forcefully terminated if it exceeds the configured timeout.

Development

# Clone the repository
git clone https://github.com/shuji-bonji/rxjs-mcp-server
cd rxjs-mcp-server

# Install dependencies
npm install

# Build
npm run build

# Run tests
npm test              # Unit tests (vitest)
npm run test:mcp      # MCP integration test
npm run test:inspector # MCP Inspector (GUI)

# Run in development
npm run dev

Release

Releases are automated via GitHub Actions and published to npm using Trusted Publisher (OIDC) — no static tokens are used, and every release carries an npm provenance attestation. See RELEASING.md for the full workflow (and initial npm setup).

Integration with Other MCP Servers

RxJS MCP Server works great alongside:

• Angular MCP - For Angular project scaffolding

• TypeScript MCP - For type checking

• ESLint MCP - For code quality

Future Meta-MCP integration will allow seamless coordination between these tools.

Architecture

┌─────────────────┐
│   AI Assistant  │
│   (Claude, etc) │
└────────┬────────┘
         │
    MCP Protocol
         │
┌────────┴────────┐
│  RxJS MCP Server│
├─────────────────┤
│ • execute_stream│
│ • generate_marble│
│ • analyze_operators│
│ • detect_memory_leak│
│ • suggest_pattern│
│ • lint_rxjs      │
└─────────────────┘

The server is built on the MCP TypeScript SDK v2 (@modelcontextprotocol/server@^2.0.0, protocol revision 2026-07-28). It speaks stdio only: src/index.ts hands the createServer() factory in src/server.ts to serveStdio(), which also serves clients that still speak the 2025 protocol revisions.

Documentation Reference System

Since v0.3.0, analyze_operators outputs three-tier documentation links for each operator and creation function:

Why include the community guide alongside official docs?

1. rxjs.dev is a client-rendered SPA. AI assistants cannot fetch its content — HTTP requests return an empty shell with JavaScript loaders. The official site is therefore a "link to hand to humans," not a source AI can read.

2. GitHub source provides raw truth. The RxJS source code (pinned at tag 7.8.2) contains JSDoc, type signatures, and implementation details. This is the primary reference for AI assistants.

3. The bilingual guide adds learning context. It organizes operators by use-case (not just alphabetically), provides runnable examples, and offers Japanese translations. For Japanese-speaking users or learners, this fills a gap that neither rxjs.dev nor raw source addresses.

Priority order

When the MCP server outputs references, it follows this priority:

1. officialUrl — always shown (authority, human-readable)

2. sourceUrl — shown when available (AI should read this)

3. guideUrl — shown when the page exists (supplementary)

If a guide page does not yet exist for an operator, the field is simply omitted (no broken link). Coverage is tracked by the URL validation CI.

Can I disable the guide references?

Currently there is no runtime option to exclude guideUrl from output. If you prefer official-only references, you can fork this server or open a feature request. A future version may support a --references=official,source flag.

Contributing

Contributions are welcome! Please feel free to submit a PR.

License

MIT

Author

Shuji Bonji

Links

• GitHub Repository

• RxJS Documentation

• Model Context Protocol