mcp code quality policy agents lint 

Harmony

Repo rules enforcement for AI agents. Harmony checks diffs against the repository rule set and blocks violations before they land.

Version

v0.1.5

License

MIT

Platforms

Node 18 or newer, Any MCP client

Interfaces

CLI, MCP

View on GitHubnpm packageMCP server

Overview

Harmony gives AI agents the same guard rails a senior reviewer would. It reads the rules a repository declares, in AGENTS.md or in a dedicated rules file, and checks every diff against them before the patch is applied. No trailing whitespace, no debug leftovers, no committed secrets, and any custom policy the repository defines.

Setup

npm install -g harmony-mcp

Add the server to your MCP client.

{
  "mcpServers": {
    "harmony": {
      "command": "harmony-mcp",
      "args": []
    }
  }
}

Define custom rules in .harmony/rules.json at the repository root. Each rule declares an id, a regex, a message, matching files, and a severity.

{
  "rules": [
    {
      "id": "no-hyphens-ui",
      "regex": "[a-z]-[a-z]",
      "message": "No dashes in UI text",
      "files": ["**/*.astro", "**/*.md", "**/*.html"],
      "severity": "warning"
    }
  ]
}

Usage

  • rules.load load the rule set for a repository. Returns the built in rules plus any custom rules.
  • rules.check check a diff against the rule set. If no diff is provided, the working tree diff of the repository is used.

Built in rules:

idseveritychecks
no-trailing-whitespacewarninglines ending in spaces or tabs
no-debug-leftoverswarningconsole.log, console.debug, debugger
no-committed-secretsblockerapi keys, passwords, tokens, secret shapes
no-tabsinfotab indentation in changed code

Typical agent instructions:

  • “Check the current diff against the repo rules.”
  • “Block any change that adds a secret.”
  • “Does the diff violate AGENTS.md?”

Gains

  • Policy violations are caught at diff time, not review time.
  • The rule set is declarative and lives with the repository.
  • Custom rules encode conventions that generic linters cannot express.
  • Deterministic output. The same diff produces the same findings.

Repository