@kernlang/mcp-server

Give any AI agent the ability to write, compile, review, and self-correct .kern code through MCP.

What your agent gets

The KERN MCP server exposes the full compiler, reviewer, and language schema. An agent using this server can:

Ask what it can write — schema returns the full language spec as JSON
Compile .kern to any target — Next.js, React, Vue, Express, FastAPI, MCP servers, and more
Self-correct from errors — compile-json returns structured diagnostics with line numbers and suggestions
Review code — 98 static analysis rules with taint tracking and OWASP coverage
Scan MCP servers — 12 security rules mapped to OWASP MCP Top 10

Quick start

Claude Desktop

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

{
  "mcpServers": {
    "kern": {
      "command": "npx",
      "args": ["@kernlang/mcp-server"]
    }
  }
}

Cursor

Add to .cursor/mcp.json in your project:

{
  "mcpServers": {
    "kern": {
      "command": "npx",
      "args": ["@kernlang/mcp-server"]
    }
  }
}

Claude Code

claude mcp add kern -- npx @kernlang/mcp-server

VS Code / Windsurf

Add to your MCP settings:

{
  "kern": {
    "command": "npx",
    "args": ["@kernlang/mcp-server"]
  }
}

Hosted endpoint (no install)

KERN runs a live MCP server at https://kernlang.dev/api/mcp. Point any MCP client that supports Streamable HTTP at this URL — no npm install required.

Tools

Tool	Description
`compile`	Compile .kern source to any of 12 targets. Returns generated code.
`compile-json`	Compile with structured JSON diagnostics (code, line, col, suggestion). For self-correction.
`schema`	Full KERN language schema as JSON — node types, props, children, shorthands.
`review`	Run 98 static analysis rules on TypeScript/JavaScript. Taint tracking, OWASP.
`review-kern`	Lint .kern source for structural issues, missing props, pattern violations.
`review-mcp-server`	Scan MCP server code for security vulnerabilities. 12 rules, OWASP MCP Top 10.
`parse`	Parse .kern to intermediate representation (IR). For debugging.
`decompile`	Convert IR back to readable .kern text.
`validate`	Validate .kern syntax without compiling.
`list-targets`	List all 12 compile targets with descriptions.
`list-nodes`	Browse node types by category with props and allowed children.

Resources

URI	Description
`kern://spec`	Full language specification — grammar, node types, shorthands, targets
`kern://examples/{category}`	Example code by category: ui, api, state-machine, mcp, terminal
`kern://targets`	Available compile targets as JSON

Prompts

write-kern

Comprehensive system prompt that teaches an LLM how to write .kern code — grammar rules, node types, style shorthands, and annotated examples for UI, API, state machines, MCP servers, hooks, and type systems.

Self-correction loop

The schema and compile-json tools enable autonomous code generation:

1. schema          → "what can I write?"
2. write .kern     → generate code using schema
3. compile-json    → "did I get it right?"
4. if errors:
     read diagnostics (line, col, suggestion)
     fix and goto 3
5. done — no human intervention needed

Each diagnostic includes code, severity, line, col, endCol, and suggestion — everything an LLM needs to fix its own mistakes.

KERN syntax at a glance

KERN uses indent-based nesting with key=value props. Comments use // or #. Inline code uses <<< ... >>> blocks.

// Comments work with // or #
# This is also a comment

doc text="User management API"
server name=UserAPI port=3001
  middleware name=cors
  middleware name=json

  route GET /api/users
    auth required
    handler <<<
      const users = await db.query('SELECT * FROM users');
      res.json(users);
    >>>

// State machine — 7 lines → 140+ lines TypeScript
machine name=Order initial=pending
  transition from=pending to=confirmed event=confirm
  transition from=confirmed to=shipped event=ship
  transition from=shipped to=delivered event=deliver
  transition from=pending to=cancelled event=cancel

MCP Security in VS Code

The kern-mcp-security extension brings the 12 MCP security rules directly into your editor. Inline diagnostics for command injection, tool poisoning, path traversal, and more — no CLI needed.

ext install kernlang.kern-mcp-security

VS Code Marketplace →Open VSX →

MCP overview →MCP security rules →Get started with KERN →