MCP Setup

Lexicon · Model Context Protocol Server

Lexicon is a macOS prompt library with a bundled MCP server that exposes your saved prompts to any AI agent. Search, retrieve, and execute templated prompts directly from Claude, Cursor, or Windsurf.

Setting up with an AI coding agent?

Copy this page's URL and paste it into your agent. It will fetch this page and walk you through installation using the machine-readable instructions below.

Then tell your agent: "Set up the Lexicon MCP server using the instructions at this URL."

Instructions for AI Coding Agents

You are an AI coding agent. The user wants to install the Lexicon MCP server. Follow these steps exactly:

Verify Lexicon is installed. Run ls /Applications/Lexicon.app. If missing, tell the user to install Lexicon from the Mac App Store before continuing.
Confirm the bundled MCP binary exists. Run ls "/Applications/Lexicon.app/Contents/MacOS/LexiconMCP". If the binary is not at that path, check /Applications/Lexicon.app/Contents/Resources/LexiconMCP as a fallback and use whichever exists.
Ask which MCP client the user runs (Claude Desktop, Claude Code, Cursor, Windsurf, Zed). Default to Claude Desktop if unsure.
Install the server config using the client-specific steps below. Use this exact server definition under the key lexicon:
```
{
  "command": "/Applications/Lexicon.app/Contents/MacOS/LexiconMCP",
  "args": []
}
```
Restart the MCP client.
Verify. The server exposes: search_prompts, get_prompt_details, create_prompt, update_prompt, delete_prompt, execute_prompt. Call search_prompts with an empty query to list all prompts.
If a step fails, read the Troubleshooting section.

What is Lexicon MCP?

Lexicon stores your prompt library in a local SQLite database with templated variables, categories, and usage history. The MCP server lets an AI agent ask "do I have a prompt for X?" before making one up — and fills in variables on the fly.

Client Instructions

Claude Desktop

Claude Desktop menu bar → Settings → Developer → Edit Config.
Merge this into claude_desktop_config.json:

{
  "mcpServers": {
    "lexicon": {
      "command": "/Applications/Lexicon.app/Contents/MacOS/LexiconMCP",
      "args": []
    }
  }
}

Save, fully quit Claude Desktop (⌘Q), reopen.
Check the MCP server list — lexicon should show as connected.

Claude Code

claude mcp add lexicon /Applications/Lexicon.app/Contents/MacOS/LexiconMCP

Restart your Claude Code session and run /mcp.

Cursor

Cursor Settings → MCP → Add new MCP server.
Or edit ~/.cursor/mcp.json directly with the JSON above.

Windsurf / Zed / Other MCP Clients

Any stdio-transport MCP client works. Point it at the binary path with empty args.

Available Tools

search_prompts

Search your library by query, category, or tags.

get_prompt_details

Fetch full prompt text, variables, and metadata by name.

execute_prompt

Render a prompt with variable substitutions, ready to paste.

create_prompt

Save a new prompt with {{variable}} placeholders.

update_prompt

Edit an existing prompt's content, category, or variables.

delete_prompt

Remove a prompt from the library by name.

Troubleshooting

Binary not found at expected path

Run find /Applications/Lexicon.app -name "LexiconMCP" -type f to locate it, then update the command field.

Server connects but returns no prompts

Launch Lexicon once so the database gets created in the App Group container. The MCP server reads from the same store.

Gatekeeper blocks first launch

Run open /Applications/Lexicon.app/Contents/MacOS/LexiconMCP once manually and approve the dialog.

"execute_prompt" says variable missing

Call get_prompt_details first to see the required variable names, then pass them all in the arguments object.