name: add-mcp description: Add an MCP server to the current project. Use when the user wants to add, configure, or enable an MCP server like context7, kubernetes, playwright, storybook, or codegraphcontext. argument-hint: <server-name | "list"> allowed-tools: Read, Glob, Grep, Edit, Write, Bash(devenv:*)

Add MCP Server

Add an MCP server configuration to the current project.

Instructions

Step 1: Identify the server

If the argument is list or empty, read all files in the servers/ directory next to this SKILL.md (use Glob on ~/.claude/skills/add-mcp/servers/*.md) and list available presets with a one-line description of each.

Otherwise, match the argument to a preset server name. If a matching preset exists, read its file from ~/.claude/skills/add-mcp/servers/. If no preset matches, ask the user for the server details (command, args, env, or URL).

Step 2: Detect project setup

Check whether the project uses devenv by looking for a devenv.nix file in the project root.

Step 3: Add the server

If the project has devenv.nix:

Add the server to claude.code.mcpServers in devenv.nix. Use the "devenv" snippet from the preset file. Make sure claude.code.enable = true; is present. If config is not already in the function arguments, add it.

Example structure in devenv.nix:

claude.code.mcpServers = {
  server-name = {
    type = "stdio";
    command = "npx";
    args = [ "-y" "package-name" ];
  };
};

After editing, tell the user to let direnv reload (or run devenv shell) so the .mcp.json is regenerated.

If the project does NOT have devenv.nix:

Add the server to .mcp.json in the project root. Create the file if it doesn't exist. Use the "mcp.json" snippet from the preset file.

The file structure is:

{
  "mcpServers": {
    "server-name": {
      "command": "...",
      "args": ["..."]
    }
  }
}

Merge into existing .mcp.json if one exists — don't overwrite other servers.

Step 4: Permissions

Check .claude/settings.json (project-level) for a permissions allow list. If one exists and uses granular MCP permissions, remind the user they may need to add mcp__<server-name> entries. If enableAllProjectMcpServers is set globally, this is not needed.

Guidelines

• Never remove or modify existing MCP server entries unless the user asks
• Keep devenv.nix edits minimal — only touch claude.code.mcpServers
• If the preset needs a package (e.g., chromium for playwright), mention it but let the user decide whether to add it to devenv packages